ANALOG DEVICES ADN2850 Service Manual

1024-Position Digital Resistor

ADN2850

Rev. E

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

Trademarks and registered trademarks are the property of their respective owners.

Fax: [phone] ©2004–2012 Analog Devices, Inc. All rights reserved.

ADDR

DECODE

ADN2850

RDAC1

SERIAL

INTERFACE

CS

CLK

SDI

SDO

PR

WP

RDY

RDAC1

REGISTER

EEMEM1

CURRENT
MONITOR

EEMEM2

26 BYTES

RTOL*

USER EEMEM

POWER-ON

RESET

W1
B1

RDAC2

W2
B2

V

DD

V

1

V

2

EEMEM

CONTROL

*R

WB

FULL SCALE TOLERANCE.

02660-001

V

SS

GND

RDAC1

REGISTER

I

1

I

2

Data Sheet

FEATURES

Dual-channel, 1024-position resolution
25 kΩ, 250 kΩ nominal resistance
Maximum ±8% nominal resistor tolerance error
Low temperature coefficient: 35 ppm/°C

2.7 V to 5 V single supply or ±2.5 V dual supply
Current monitoring configurable function
SPI-compatible serial interface
Nonvolatile memory stores wiper settings
Power-on refreshed with EEMEM settings
Permanent memory write protection
Resistance tolerance stored in EEMEM
26 bytes extra nonvolatile memory for user-defined

information
1M programming cycles
100-year typical data retention

APPLICATIONS

SONET, SDH, ATM, Gigabit Ethernet, DWDM laser diode

driver, optical supervisory systems
Mechanical rheostat replacement
Instrumentation gain adjustment
Programmable filters, delays, time constants
Sensor calibration

GENERAL DESCRIPTION

The ADN2850 is a dual-channel, nonvolatile memory1, digitally
controlled resistors
guaranteed maximum low resistor tolerance error of ±8%. The
device performs the same electronic adjustment function as a
mechanical rheostat with enhanced resolution, solid state
reliability, and superior low temperature coefficient
performance. The versatile programming of the ADN2850 via
an SPI®-compatible serial interface allows 16 modes of
operation and adjustment including scratchpad programming,
memory storing and restoring, increment/decrement, ±6 dB/step
log taper adjustment, wiper setting readback, and extra EEMEM
for user-defined information such as memory data for other
components, look-up table, or system identification
information.

1

The terms nonvolatile memory and EEMEM are used interchangeably.

2

The terms digital resistor and RDAC are used interchangeably.

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

2

with 1024-step resolution, offering

Nonvolatile Memory, Dual

FUNCTIONAL BLOCK DIAGRAM

Figure 1.

In the scratchpad programming mode, a specific setting can
be programmed directly to the RDAC

2

register, which sets the
resistance between Terminal W and Terminal B. This setting can
be stored into the EEMEM and is restored automatically to the
RDAC register during system power-on.

The EEMEM content can be restored dynamically or through
external

EE

PR

AA strobing, and a AA

EE

WP

AA function protects EEMEM

contents. To simplify the programming, the independent or
simultaneous linear-step increment or decrement commands
can be used to move the RDAC wiper up or down, one step at a
time. For logarithmic ±6 dB changes in the wiper setting, the
left or right bit shift command can be used to double or halve the
RDAC wiper setting.

The ADN2850 patterned resistance tolerance is stored in the
EEMEM. The actual full scale resistance can, therefore, be
known by the host processor in readback mode. The host can

1

execute the appropriate resistance step through a software
routine that simplifies open-loop applications as well as
precision calibration and tolerance matching applications.

The ADN2850 is available in the 5 mm × 5 mm 16-lead frame
chip scale LFCSP and thin, 16-lead TSSOP package. The part is
guaranteed to operate over the extended industrial temperature
range of −40°C to +85°C.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]

www.analog.com

ADN2850 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Electrical Characteristics—25 kΩ, 250 kΩ Vers io n s ............... 3

Interface Timing and EEMEM Reliability Characteristics—

25 kΩ, 250 kΩ Versions ............................................................... 5

Absolute Maximum Ratings ............................................................ 7

ESD Caution .................................................................................. 7

Pin Configuration and Function Descriptions ............................. 8

Typical Performance Characteristics ........................................... 10

Test Circuits ................................................................................. 12

Theory of Operation ...................................................................... 13

Scratchpad and EEMEM Programming .................................. 13

Basic Operation .......................................................................... 13

EEMEM Protection .................................................................... 14

Digital Input and Output Configuration................................. 14

Serial Data Interface ................................................................... 14

Daisy-Chain Operation ............................................................. 14

Terminal Voltage Operating Range ......................................... 15

Advanced Control Modes ......................................................... 17

RDAC Structure.......................................................................... 18

Programming the Variable Resistor ......................................... 19

Programming Examples ............................................................ 19

EVA L-ADN2850SDZ Evaluation Kit ....................................... 20

Applications Information .............................................................. 21

Gain Control Compensation .................................................... 21

Programmable Low-Pass Filter ................................................ 21

Programmable Oscillator .......................................................... 21

Optical Transmitter Calibration with ADN2841 ................... 22

Incoming Optical Power Monitoring ...................................... 22

Resistance Scaling ...................................................................... 23

Resistance Tolerance, Drift, and Temperature Coefficient

Mismatch Considerations ......................................................... 24

RDAC Circuit Simulation Model ............................................. 24

Outline Dimensions ....................................................................... 25

Ordering Guide .......................................................................... 25

REVISION HISTORY

6/12—Rev. D to Rev. E

Changes to Table 1 Conditions ....................................................... 4

Removed Positive Supply Current RDY and/or SDO Floating
Parameters and Negative Supply Current RDY and/or SDO

Floating Parameters, Table 1 ........................................................... 4

Updated Outline Dimensions ....................................................... 25

Added Endnote 2 to Ordering Guide .......................................... 25

4/11—Rev. C to Rev. D

Changes to Figure 10 ...................................................................... 10

4/11—Rev. B to Rev. C

Updated Format .................................................................. Universal

Changes to EEMEM Performance ................................... Universal

Changes to Features Section............................................................ 1

Changes to Applications Section .................................................... 1

Changes to General Description Section ...................................... 1

Changes to Figure 1 .......................................................................... 1

Changes to Specifications Section .................................................. 3

Changes to Table 2 ............................................................................ 5

Changes to Absolute Maximum Ratings Section ......................... 7

Changes to Pin Configuration and Function Descriptions

Section ................................................................................................ 8

Changes to Typical Performance Characteristics Section ........ 10

Added Figure 15, Figure 16, Figure 17 ........................................ 11

Changes to Figure 21 ...................................................................... 12

Changes to Theory of Operation Section.................................... 13

Changes to Figure 25 ...................................................................... 14

Changes to Programming Variable Resister Section ................. 19

Changes to Table 13 ....................................................................... 19

Changes to EVAL-ADN2850EBZ Evaluation Kit Section ........ 20

Added Gain Control Compensation Section.............................. 21

Added Programmable Low-Pass Filter Section .......................... 21

Added Programmable Oscillator Section .................................... 21

Added Resistance Tolerance, Drift, and Temperature Coeffcient

Mistmatch Considerations Section .............................................. 24

Changes to Outline Dimensions Section .................................... 25

Changes to Ordering Guide .......................................................... 25

9/02—Rev. A to Rev. B

Changes to General Description ..................................................... 1

Changes to Electrical Characteristics ............................................. 2

Changes to Calculating Actual Full-Scale Resistance Section ..... 9

Changes to Table VI .......................................................................... 9

Updated Outline Dimensions ....................................................... 18

Rev. E | Page 2 of 28

Data Sheet ADN2850

Capacitance Wx3

CW

f = 1 MHz, measured to GND,

80 pF
DIGITAL INPUTS AND OUTPUTS

Dual-Supply Power Range

VDD/VSS

±2.25

±2.75

V

Power Dissipation6

P

VIH = VDD or VIL = GND

10

30

µW

Power Supply Sensitivity3

PSS

∆VDD = 5 V ± 10%

0.006

0.01

%/%

SPECIFICATIONS

ELECTRICAL CHARACTERISTICS—25 kΩ, 250 kΩ VERSIONS

VDD = 2.7 V to 5.5 V, VSS = 0 V; VDD = 2.5 V, VSS = −2.5 V, VA = VDD, VB = VSS, −40°C < TA < +85°C, unless otherwise noted. These
specifications apply to versions with a date code 1209 or later.

Table 1.

Parameter Symbol Conditions Min Typ1 Max Unit

DC CHARACTERISTICS—RHEOSTAT

MODE (All RDACs)
Resolution N 10
Resistor Differential Nonlinearity2 R-DNL RWB −1 +1 LSB
Resistor Integral Nonlinearity2 R-INL RWB −2 +2 LSB
Nominal Resistor Tolerance ∆RWB/RWB Code = full scale −8 +8 %
Resistance Temperature Coefficient3 (∆RWB/RWB)/

Wiper Resistance RW Code = half scale
VDD = 5 V 30 60 Ω

VDD = 3 V 50 Ω

Nominal Resistance Match3 R

RESISTOR TERMINALS

Terminal Voltage Range3 VB, VW VSS VDD V
Capacitance Bx3 CB f = 1 MHz, measured to GND,

6

∆T × 10

Code = full scale ±0.1 %

WB1/RWB2

Code = full scale 35 ppm/°C

11 pF

code = half-scale

Common-Mode Leakage Current

3, 4

ICM VW = VDD/2 0.01 ±1 µA

Input Logic 3

High VIH VDD = 5 V 2.4 V
VDD = 2.7 V 2.1 V
VDD = +2.5 V, VSS = −2.5 V 2.0 V
Low VIL VDD = 5 V 0.8 V
VDD = 2.7 V 0.6 V

VDD = +2.5 V, VSS = −2.5 V 0.5 V

code = half-scale

Output Logic High (SDO, RDY) VOH R
Output Logic Low VOL IOL = 1.6 mA, V

= 2.2 kΩ to 5 V (see Figure 25) 4.9 V

PULL-UP

= 5 V (see Figure 25) 0.4 V

LOGIC

Input Current IIL VIN = 0 V or VDD ±1 µA
Input Capacitance3 CIL 5 pF

POWER SUPPLIES

Single-Supply Power Range VDD VSS = 0 V 2.7 5.5 V

Positive Supply Current IDD VIH = VDD or VIL = GND 2 5 µA
Negative Supply Current ISS VDD = +2.5 V, VSS = −2.5 V
VIH = VDD or VIL = GND −4 −2 µA
EEMEM Store Mode Current IDD (store) VIH = VDD or VIL = GND,

= GND, ISS ≈ 0

V

SS

2 mA

ISS (store) VDD = +2.5 V, VSS = −2.5 V −2 mA
EEMEM Restore Mode Current5 IDD (restore) VIH = VDD or VIL = GND,

V

= GND, ISS ≈ 0

SS

320 µA

ISS (restore) VDD = +2.5 V, VSS = −2.5 V −320 µA

DISS

Rev. E | Page 3 of 28

ADN2850 Data Sheet

Parameter Symbol Conditions Min Typ1 Max Unit

CURRENT MONITOR TERMINALS

Current Sink at V1 I1 0.0001 10 mA
Current Sink at V2 I2 0.0001 10 mA

DYNAMIC CHARACTERISTICS

Resistor Noise Density e

RWB = 25 kΩ/250 kΩ, TA = 25°C 20/64

Analog Crosstalk CT VBX = GND, Measured VW1 with VW2 =

1

Typicals represent average readings at 25°C and VDD = 5 V.

2

Resistor position nonlinearity error (R-INL) is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper

positions. R-DNL measures the relative step change from ideal between successive tap positions. The maximum current in each code is defined by I
(see Figure 20).

3

Guaranteed by design and not subject to production test.

4

Common-mode leakage current is a measure of the dc leakage from any Terminal B, or Terminal W to a common-mode bias level of VDD/2.

5

EEMEM restore mode current is not continuous. Current is consumed while EEMEM locations are read and transferred to the RDAC register.

6

P

is calculated from (IDD × VDD) + (ISS × VSS).

DISS

7

All dynamic characteristics use VDD = +2.5 V and VSS = −2.5 V.

3, 7

Code= full scale

N_WB

−95/−80

1 V

, f = 1 kHz, Code 1 = midscale,

RMS

Code 2 = midscale,

= 25 kΩ/250 kΩ

R

WB

WB = (VDD − 1)/RWB.

nV/√Hz
dB

Rev. E | Page 4 of 28

Data Sheet ADN2850

Input Clock Pulse Width

t4, t5

Clock level high or low

10

ns

CLK to SDO Propagation Delay

t10

RP = 2.2 kΩ, CL < 20 pF

50

ns

CLK to SDO Data Hold Time

t11

RP = 2.2 kΩ, CL < 20 pF

0

ns

Read EEMEM Time4

t16

Applies to instructions 0x8, 0x9, 0x10

7 30

µs

Data Retention

100 Years

INTERFACE TIMING AND EEMEM RELIABILITY CHARACTERISTICS—25 kΩ, 250 kΩ VERSIONS

Guaranteed by design and not subject to production test. See the Timing Diagrams section for the location of measured values. All input
control voltages are specified with t
measured using both V

= 3 V and VDD = 5 V.

DD

Table 2.

Parameter Symbol Conditions Min Typ1 Max Unit

Clock Cycle Time (t

EE

AA Setup Time

CS
CLK Shutdown Time to AA

) t1 20 ns

CYC

EE

AA Rise t

CS

Data Setup Time t6 From positive CLK transition 5 ns
Data Hold Time t7 From positive CLK transition 5 ns

EE

AA

AA to SDO-SPI Line Acquire t

CS

EE

AA

AA to SDO-SPI Line Release t

CS

= tF = 2.5 ns (10% to 90% of 3 V) and timed from a voltage level of 1.5 V. Switching characteristics are

R

t2 10 ns

1 t

3

40 ns

8

50 ns

2

10F

9

CYC

EE

AA

AA High Pulse Width11F

CS

AA

EE AAHigh to AA

CS
RDY Rise to AA

EE

AA

AA Rise to RDY Fall Time t

CS

CS

CS

Store EEMEM Time

EE

AA

AA Rise to Clock Rise/Fall Setup t

CS
Preset Pulse Width (Asynchronous)
Preset Response Time to Wiper Setting
Power-On EEMEM Restore Time
FLASH/EE MEMORY RELIABILITY

Endurance

1

Typicals represent average readings at 25°C and VDD = 5 V.

2

Propagation delay depends on the value of VDD, R

3

Valid for commands that do not activate the RDY pin.

4

RDY pin low only for Instruction 2, Instruction 3, Instruction 8, Instruction 9, Instruction 10, and the PR hardware pulse: CMD_8 ~ 20 µs; CMD_9, CMD_10 ~ 7 µs;

CMD_2, CMD_3 ~ 15 ms,

5

Store EEMEM time depends on the temperature and EEMEM write cycles. Higher timing is expected at lower temperature and higher write cycles.

6

Not shown in Figure 2 and Figure 3.

7

Endurance is qualified to 100,000 cycles per JEDEC Standard 22, Method A117 and measured at −40°C, +25°C, and +85°C.

8

Retention lifetime equivalent at junction temperature (TJ) = 85°C per JEDEC Standard 22, Method A117. Retention lifetime based on an activation energy of 1 eV

3

t12

EE

3

AA High

t13 4 t

EE

AA Fall t

4,

5

12F

13F

t16 Applies to instructions 0x2, 0x3 15 50 ms

6

14F

t

6

6

t

0 ns

14

0.15 0.3 ms

15

10 ns

17

50 ns

PRW

t

PRESP

EEMEM

AA

EE

pulsed low to refresh wiper positions

AA

PR

10 ns

30 µs

30 µs

7

15F

TA = 25°C 1

100

8

16F

, and CL.

PULL-UP

PR

hardware pulse ~ 30 µs.

derates with junction temperature in the Flash/EE memory.

CYC

MCycles
kCycles

Rev. E | Page 5 of 28

ADN2850 Data Sheet

CPOL = 1

t

12

t

13

t

3

t

17

t

9

t

11

t

5

t

4

t

2

t

1

CLK

t

8

B24*

B23 (MSB) B0 (LSB)

B23 (MSB)

HIGH
OR LOW

HIGH
OR LOW

B23 B0

B0 (LSB)

RDY

CPHA = 1

t

10

t

7

t

6

t

14

t

15

t

16

*THE EXTRA BIT THAT IS NOT DEFINED IS NORMALLYTHE LSB OF THE CHARACTER PREVIOUSLY TRANSMITTED.

THE CPOL = 1 MICROCONTROLLER COMMAND ALIGNS THE INCOMING DATATO THE POSITIVE EDGE OF THE CLOCK.

SDO

SDI

CS

02660-002

t

12

t

13

t

3

t

17

t

9

t

11

t

5

t

4

t

2

t

1

CLK

CPOL = 0

t

8

B23 (MSB OUT) B0 (LSB)

SDO

B23 (MSB IN)

B23 B0

HIGH
OR LOW

HIGH
OR LOW

B0 (LSB)

SDI

RDY

CPHA = 0

t

10

t

7

t

6

t

14

t

15

t

16

*THE EXTRA BIT THAT IS NOT DEFINED IS NORMALLY THE MSB OF THE CHARACTER JUST RECEIVED.

THE CPOL = 0 MICROCONTROLLER COMMAND ALIGNS THE INCOMING DATA TO THE POSITIVE EDGE OF THE CLOCK.

*

CS

02660-003

Timing Diagrams

Figure 2. CPHA = 1 Timing Diagram

Figure 3. CPHA = 0 Timing Diagram

Rev. E | Page 6 of 28

Data Sheet ADN2850

Vapor Phase (60 sec)

215°C

Junction-to-Case θJC, TSSOP-16

28°C/W

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Table 3.

Parameter Rating

VDD to GND –0.3 V to +7 V
VSS to GND +0.3 V to −7 V

to VSS 7 V

V

DD

VB, VW to GND VSS − 0.3 V to VDD + 0.3 V

, IW

I

B

Pulsed0F0F1 ±20 mA
Continuous

±2 mA

Digital Input and Output Voltage to GND −0.3 V to VDD + 0.3 V

2

1F1F

Operating Temperature Range

−40°C to +85°C
Maximum Junction Temperature (TJ max) 150°C
Storage Temperature Range

−65°C to +150°C

Lead Temperature, Soldering

Infrared (15 sec) 220°C

Thermal Resistance

Junction-to-Ambient θJA,TSSOP-16 150°C/W
Junction-to-Ambient θ

,LFSCP-16 35°C/W

JA

Package Power Dissipation (TJ max − TA)/θJA

1

Maximum terminal current is bounded by the maximum current handling of

the switches, maximum power dissipation of the package, and maximum
applied voltage across any two of the A, B, and W terminals at a given
resistance.

2

Includes programming of nonvolatile memory.

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

ESD CAUTION

Rev. E | Page 7 of 28

ADN2850 Data Sheet

SDI
SDO
GND

V1

V

SS

W1

CLK

B1

CS
PR
WP
V

DD

V2
W2
B2

RDY

1

2

3

4

5

6

7

8

16

15

14

13
12

11

10

9

ADN2850

TOP VIEW

(Not to Scale)

02660-005

Pin No.

Mnemonic

Description

2

SDI

Serial Data Input. Shifts in one bit at a time on positive clock CLK edges. MSB loads first.

7

W1

Wiper Terminal of RDAC1. ADDR (RDAC1) = 0x0.

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

Figure 4. Pin Configuration

Table 4. Pin Function Descriptions

1 CLK Serial Input Register Clock. Shifts in one bit at a time on positive clock edges.

3 SDO Serial Data Output. Serves readback and daisy-chain functions. Command 9 and Command 10 activate the SDO

output for the readback function, delayed by 24 or 25 clock pulses, depending on the clock polarity before and
after the data-word (see Figure 2 and Figure 3). In other commands, the SDO shifts out the previously loaded SDI
bit pattern, delayed by 24 or 25 clock pulses depending on the clock polarity (see Figure 2 and Figure 3). This
previously shifted out SDI can be used for daisy-chaining multiple devices. Whenever SDO is used, a pull-up

resistor in the range of 1 kΩ to 10 kΩ is needed.
4 GND Ground Pin, Logic Ground Reference.
5 VSS Negative Supply. Connect to 0 V for single-supply applications. If VSS is used in dual supply, it must be able to sink

2 mA for 15 ms when storing data to EEMEM.
6 V1 Log Output Voltage 1. Generates voltage from an internal diode configured transistor.

8 B1 Terminal B of RDAC1.
9
10

B2 Terminal B of RDAC2.

W2 Wiper terminal of RDAC2. ADDR (RDAC2) = 0x1.
11 V2 Log Output Voltage 2. Generates voltage from an internal diode configured transistor.
12
13

14 AA

15 AA
16 RDY Ready. Active high open-drain output. Identifies completion of Instruction 2, Instruction 3, Instruction 8,

VDD Positive Power Supply.

EE

AA

Optional Write Protect. When active low, AA

WP

CMD_1 and COMD_8 refresh the RDAC register from EEMEM. Tie AA

EE

Optional Hardware Override Preset. Refreshes the scratchpad register with current contents of the EEMEM

PR

register. Factory default loads midscale 512
at the logic high transition. Tie AA

EE

Serial Register Chip Select Active Low. Serial register operation takes place when AA

CS

Instruction 9, Instruction 10, and

PR

EE

AA to V

AA

PR

EE

AA.

EE

AA

prevents any changes to the present contents, except AA

WP

until EEMEM is loaded with a new value by the user. AA

10

, if not used.

DD

WP

EE

AA to V

, if not used.

DD

CS

EE

AA returns to logic high.

PR

PR

EE

AA

strobe.

EE

AA is activated

Rev. E | Page 8 of 28

Data Sheet ADN2850

A

DN2850

TOP VIEW

(Not to Scale)

PIN 1

INDICATOR

SS

1

SDI
16

1SDO
2GND

(EXPOSED

3V
4V

5
1

W

CLK
15

PAD)

6
B1

CS

RDY
14

13

12 PR
11 WP
10 V

DD

9V

2

8

7

2

B2

W

02660-105

NOTES

1. THE EXPOSED PAD IS LEFT FLOATING

SS

OR IS TIED TO V

.

Figure 5. Pin Configuration

Table 5. Pin Function Descriptions

Pin No. Mnemonic Description

1 SDO

Serial Data Output. Serves readback and daisy-chain functions. Command 9 and Command 10 activate the SDO
output for the readback function, delayed by 24 or 25 clock pulses, depending on the clock polarity before and
after the data-word (see Figure 2 and Figure 3). In other commands, the SDO shifts out the previously loaded SDI
bit pattern, delayed by 24 or 25 clock pulses depending on the clock polarity (see Figure 2 and Figure 3). This
previously shifted out SDI can be used for daisy-chaining multiple devices. Whenever SDO is used, a pull-up

resistor in the range of 1 kΩ to 10 kΩ is needed.
2 GND Ground Pin, Logic Ground Reference.
3 VSS

Negative Supply. Connect to 0 V for single-supply applications. If V

is used in dual supply, it must be able to sink

SS

2 mA for 15 ms when storing data to EEMEM.
4 V1 Log Output Voltage 1. Generates voltage from an internal diode configured transistor.
5 W1 Wiper terminal of RDAC1. ADDR (RDAC1) = 0x0.
6 B1 Terminal B of RDAC1.
7 B2 Terminal B of RDAC2.
8 W2 Wiper terminal of RDAC2. ADDR (RDAC2) = 0x1.
9 V2 Log Output Voltage 2. Generates voltage from an internal diode configured transistor.
10 VDD Positive Power Supply.
11

12

13

E

AWP

Optional Write Protect. When active low, AWP

E

APR

Optional Hardware Override Preset. Refreshes the scratchpad register with current contents of the EEMEM

E

ACS

Serial Register Chip Select Active Low. Serial register operation takes place when ACS

14 RDY

CMD_1 and COMD_8 refresh the RDAC register from EEMEM. Tie

register. Factory default loads midscale until EEMEM is loaded with a new value by the user.

at the logic high transition. Tie

Ready. Active high open-drain output. Identifies completion of Instruction 2, Instruction 3, Instruction 8,

Instruction 9, Instruction 10, and

E

A

APR

to VDD, if not used.

E

A

APR

.

E

A

prevents any changes to the present contents, except APR

E

A

AWP

to VDD, if not used.

E

A

returns to logic high.

15 CLK Serial Input Register Clock. Shifts in one bit at a time on positive clock edges.
16 SDI Serial Data Input. Shifts in one bit at a time on positive clock CLK edges. MSB loads first.
EP Exposed Pad. The exposed pad is left floating or is tied to VSS.

E

A

APR

is activated

E

A

strobe.

Rev. E | Page 9 of 28

ADN2850 Data Sheet

DIGITAL CODE

0 200 400 600 1000

INL ERROR (LSB)

800

0.20

–0.20

–0.15

–0.10

–0.05

0

0.05

0.10

0.15

–40°C

+25°C

+85°C

02660-008

DIGITAL CODE

0 200 400 600 1000

DNL ERROR (LSB)

800

0.20

–0.15

–0.10

–0.05

0

0.05

0.10

0.15

02660-009

–40°C

+25°C

+85°C

02660-011

CODE (Decimal)

RHEOSTAT MODE TEMPCO (ppm/°C)

200

180

160

140

120

100

80

60

40

20

0

0 1023768512256

25kΩ
250kΩ

CODE (Decimal)

0 200 400 800600 1000

WIPER ON RESISTANCE (Ω)

60

50

40

30

20

10

0

2.7V

3.0V

3.3V

5.0V

5.5V

02660-012

TEMPERATURE (°C)

–40 –20 0 25 40 60 85

I

DD

/I

SS

(µA)

3

–3

–2

–1

0

1

2

I

DD

= 2.7V

I

DD

= 3.3V

I

DD

= 3.0V

I

DD

= 5.5V

IDD= 5.0V

ISS= 2.7V
I

SS

= 3.3V

I

SS

= 3.0V

I

SS

= 5.5V

I

SS

= 5.0V

02660-013

FREQUENCY (MHz)

1 1098765432

I

DD

(µA)

50

10

20

30

40

0

FULL SCALE
MIDSCALE
ZERO SCALE

02660-014

TYPICAL PERFORMANCE CHARACTERISTICS

Figure 6. R-INL vs. Code, TA = −40°C, +25°C, +85°C Overlay, RAB = 25 kΩ

Figure 7. R-DNL vs. Code, TA = −40°C, +25°C, +85°C Overlay, RAB = 25 kΩ

Figure 9. Wiper On Resistance vs. Code

Figure 10. IDD vs. Temperature, RAB = 25 kΩ

Figure 8. (∆RWB/RWB)/∆T × 106 Rheostat Mode Tempco

Figure 11. IDD vs. Clock Frequency

Rev. E | Page 10 of 28

Data Sheet ADN2850

0

100

200

300

400

I

DD

(µA)

VDIO (V)

2.7V

3.0V

3.3V

5.0V

5.5V

02660-015

0 1 2 3 4 5

FREQUENCY ( Hz )

10 100 1k 10k 100k 1M

PSRR (dB)

–80

–60

–70

–50

–40

–30

–20

–10

0

RAB= 250kΩ

R

AB

= 25kΩ

02660-019

VDD = 5V ± 10% AC
V

SS

= 0V, IW (25k) = 200µA

I

W

(250k) = 20µA, V

B

= 0V

MEASURED AT V

W

WITH CO DE = 0x200

T

A

= 25°C

02660-020

VDD= 5V
I

W

= 200µA

V

B

= 0V

T

A

= 25°C

1V/DIV

10µs/DIV

V

DD

VW(FULL SCALE)

2.5982

2.5975

2.5970

2.5965

2.5960

2.5955

2.5950

2.5945

2.5940

2.5935

2.5930

2.5925

2.5920

2.5915

2.5910

2.5905

2.5900

2.5895

2.5890

2.5885

2.5880

2.5873
–19.8 –10 0 10 20 30 40 50 60 70 80

02660-115

VOLTAGE (V)

TIME (µs)

V

DD

= 5V

V

SS

= GND

V

B

= V

SS

I

W

= 200µA

2.2492

2.2490

2.2485

2.2425

0 50–39.8 100 150 200 250 300

02660-116

VOLTAGE (V)

TIME (µs)

2.2480

2.2475

2.2470

2.2465

2.2460

2.2455

2.2450

2.2445

2.2440

2.2435

2.2430

360

VDD = 5V
V

SS

= GND

V

B

= V

SS

IW = 20µA

2.80

2.50

0.80.7 0.9 1.0 1.1 1.2 1.3 1.4 1.5

02660-117

TIME (µs)

2.75

2.70

2.65

WIPER VOLTAGE (V)

2.60

2.55

VDD= 5V
V

SS

= GND

V

B

= GND

I

W

(25k) = 200µA

I

W

(250k) = 20µA

Figure 12. IDD vs Digital Input Voltage

Figure 13. PSRR vs. Frequency

Figure 15. Midscale Glitch Energy, RAB = 25 kΩ, Code 0x200 to Code 0x1FF

Figure 16. Midscale Glitch Energy, RAB = 250 kΩ, Code 0x200 to Code 0x1FF

Figure 14. Power-On Reset

Figure 17. Digital Feedthrough

Rev. E | Page 11 of 28

ADN2850 Data Sheet

02660-023

CS (5V/DIV)

CLK (5V/DIV)

SDI (5V/DIV)

I

DD

(2mA/DIV)

V

DD

= 5V

T

A

= 25°C

CODE (Decimal)

02660-025

100

1

0.01
1023

THEORECTICAL (I

WB_MAX

– mA)

0.1

10

896768640512384128 2560

TA= 25°C

R

WB

= 25kΩ

R

WB

= 250kΩ

W

B

I

W

DUT

V

MS

02660-026

W

B

I

W

= V

DD

/R

NOMINAL

V

MS1

V

W

RW= V

MS1/IW

02660-028

W

B

V

MS

V+ = V

DD

±10%

PSRR (dB) = 20 LOG

ΔV

DD

(

)

~

V

DD

PSS (%/%) =

V+

ΔV

MS

ΔV

DD

%

ΔV

MS

%

02660-029

IW= VDD/(R

NOMINAL

/ 2)

CODE = Mid Scale

+

–

DUT

0.1V

V

SS

TO V

DD

RSW=

0.1V
I

SW

I

SW

W

B

02660-033

DUT

V

SS

I

CM

W

B

V

DD

NC

V

CM

GND

NC = NO CONNECT

02660-034

Figure 18. IDD vs. Time when Storing Data to EEMEM

TEST CIRCUITS

Figure 20 to Figure 24 define the test conditions used in the Specifications section.

Figure 20. Resistor Position Nonl inearity Error (Rheostat Operation; R-INL, R-DNL)

Figure 21. Wiper Resistance

Figure 19. I

WB_MAX

vs. Code

Figure 23. Incremental On Resistance

Figure 24. Common-Mode Leakage Current

Figure 22. Power Supply Sensitivity (PSS, PSRR)

Rev. E | Page 12 of 28

Data Sheet ADN2850

THEORY OF OPERATION

The ADN2850 digital programmable resistor is designed to
operate as a true variable resistor. The resistor wiper position is
determined by the RDAC register contents. The RDAC register
acts as a scratchpad register, allowing unlimited changes of
resistance settings. The scratchpad register can be programmed
with any position setting using the standard SPI serial interface by
loading the 24-bit data-word. In the format of the data-word, the
first four bits are commands, the following four bits are addresses,
and the last 16 bits are data. When a specified value is set, this
value can be stored in a corresponding EEMEM register. During
subsequent power-ups, the wiper setting is automatically loaded to
that value.

Storing data to the EEMEM register takes about 15ms and
consumes approximately 2 mA. During this time, the shift
register is locked, preventing any changes from taking place.
The RDY pin pulses low to indicate the completion of this
EEMEM storage. There are also 13 addresses with two bytes
each of user-defined data that can be stored in the EEMEM
register from Address 2 to Address 14.

The following instructions facilitate the programming needs of
the user (see Tab l e 8 for details):

0. Do nothing.

1. Restore EEMEM content to RDAC.

2. Store RDAC setting to EEMEM.

3. Store RDAC setting or user data to EEMEM.

4. Decrement by 6 dB.

5. Decrement all by 6 dB.

6. Decrement by one step.

7. Decrement all by one step.

8. Reset EEMEM content to RDAC.

9. Read EEMEM content from SDO.

10. Read RDAC wiper setting from SDO.

11. Write data to RDAC.

12. Increment by 6 dB.

13. Increment all by 6 dB.

14. Increment by one step.

15. Increment all by one step.

Table 14 to Tabl e 20 provide programming examples that use
some of these commands.

SCRATCHPAD AND EEMEM PROGRAMMING

The scratchpad RDAC register directly controls the position of
the digital resistor wiper. For example, when the scratchpad register
is loaded with all 0s, the wiper is connected to Te rm in a l B of the
variable resistor. The scratchpad register is a standard logic
register with no restriction on the number of changes allowed,
but the EEMEM registers have a program erase/write cycle
limitation.

BASIC OPERATION

The basic mode of setting the variable resistor wiper position
(programming the scratchpad register) is accomplished by
loading the serial data input register with Instruction 11 (0xB),
Address 0, and the desired wiper position data. When the proper
wiper position is determined, the user can load the serial data
input register with Instruction 2 (0x2), which stores the wiper
position data in the EEMEM register. After 15 ms, the wiper
position is permanently stored in nonvolatile memory.

Table 6 provides a programming example listing the sequence of
the serial data input (SDI) words with the serial data output
appearing at the SDO pin in hexadecimal format.

Table 6. Write and Store RDAC Settings to EEMEM Registers

SDI SDO Action

0xB00100 0xXXXXXX Writes data 0x100 to the RDAC1 register,

Wiper W1 moves to 1/4 full-scale position.

0x20XXXX 0xB00100 Stores RDAC1 register content into the

EEMEM1 register.

0xB10200 0x20XXXX Writes Data 0x200 to the RDAC2 register,

Wiper W2 moves to 1/2 full-scale position.

0x21XXXX 0xB10200 Stores RDAC2 register contents into the

EEMEM2 register.

At system power-on, the scratchpad register is automatically
refreshed with the value previously stored in the corresponding
EEMEM register. The factory-preset EEMEM value is midscale.
The scratchpad register can also be refreshed with the contents
of the EEMEM register in three different ways. First, executing
Instruction 1 (0x1) restores the corresponding EEMEM value.
Second, executing Instruction 8 (0x8) resets the EEMEM values
of both channels. Finally, pulsing the
EEMEM settings. Operating the hardware control
requires a complete pulse signal. When
logic sets the wiper at midscale. The EEMEM value is not
loaded until

EE

PR

AA

AA returns high.

EE

PR

AA pin refreshes both

PR

EE

PR

AA

AA goes low, the internal

AA

EE

AA function

Rev. E | Page 13 of 28

ADN2850 Data Sheet

VALID

COMMAND

COUNTER

COMMAND

PROCESSOR

AND ADDRESS

DECODE

(FOR DAISY
CHAIN ONLY)

SERIAL

REGISTER

CLK

SDI

5V

R

PULL-UP

SDO

GND

PR WP

ADN2850

CS

02660-037

LOGIC

PINS

V

DD

GND

INPUTS

300Ω

02660-038

V

DD

GND

INPUT

300Ω

WP

02660-039

EEMEM PROTECTION

EE

The write protect (AA
scratchpad register contents, except for the EEMEM setting,
which can still be restored using Instruction 1, Instruction 8,
and the

PR

AA

hardware EEMEM protection feature.

DIGITAL INPUT AND OUTPUT CONFIGURATION

All digital inputs are ESD protected, high input impedance that
can be driven directly from most digital sources. Active at logic

EE

PR

low,

AA

AA and AA

internal pull-up resistors are present on any digital input pins.
To avoid floating digital pins that might cause false triggering
in a noisy environment, add pull-up resistors. This is applicable
when the device is detached from the driving source when it is
programmed.

The SDO and RDY pins are open-drain digital outputs that only
need pull-up resistors if these functions are used. To optimize
the speed and power trade-off, use 2.2 kΩ pull-up resistors.

The equivalent serial data input and output logic is shown in
Figure 25
chip-select (
inputs is shown in

. The open-drain output SDO is disabled whenever

Figure 25. Equivalent Digital Input and Output Logic

WP

AA) pin disables any changes to the

EE

AA pulse. Therefore, AA

EE

WP

AA must be tied to V

EE

CS

AA

AA) is in logic high. ESD protection of the digital

EE

WP

AA can be used to provide a

, if they are not used. No

DD

Figure 26 and Figure 27.

Figure 27. Equivalent AA

EE

WP

AA Input Protection

SERIAL DATA INTERFACE

The ADN2850 contains a 4-wire SPI-compatible digital
interface (SDI, SDO,
must be loaded with MSB first. The format of the word is shown in
Table 7. The command bits (C0 to C3) control the operation of the
digital resistor according to the command shown in Table 8. A0
to A3 are the address bits. A0 is used to address RDAC1 or RDAC2.
Address 2 to Address 14 are accessible by users for extra EEMEM.
Address 15 is reserved for factory usage. Tab l e 10 provides an
address map of the EEMEM locations. D0 to D9 are the values
for the RDAC registers. D0 to D15 are the values for the EEMEM
registers.

The ADN2850 has an internal counter that counts a multiple of
24 bits (a frame) for proper operation. For example, ADN2850
works with a 24-bit or 48-bit word, but it cannot work properly
with a 23-bit or 25-bit word. To prevent data from mislocking
(due to noise, for example), the counter resets, if the count is not a
multiple of four when
is multiple of four. In addition, the ADN2850 has a subtle

CS

feature that, if

AA

repeats the previous command (except during power-up). As a

the CLK or

result, care must be taken to ensure that no excessive noise exists in

EE

CS

AA

AA line that might alter the effective number-of-bits

pattern.

The SPI interface can be used in two slave modes: CPHA = 1,
CPOL = 1 and CPHA = 0, CPOL = 0. CPHA and CPOL refer to
the control bits that dictate SPI timing in the following
MicroConverters® and microprocessors: ADuC812, ADuC824,
M68HC11, MC68HC16R1, and MC68HC916R1.

EE

CS

AA

AA, and CLK). The 24-bit serial data-word

EE

CS

AA

AA

goes high but remains in the register if it

EE

AA is pulsed without CLK and SDI, the part

Figure 26. Equivalent ESD Digital Input Protection

Rev. E | Page 14 of 28

DAISY-CHAIN OPERATION

The serial data output pin (SDO) serves two purposes. It can be
used to read the contents of the wiper setting and EEMEM values
using Instruction 10 and Instruction 9, respectively. The remaining
instructions (Instruction 0 to Instruction 8, Instruction 11 to
Instruction 15) are valid for daisy-chaining multiple devices in
simultaneous operations. Daisy-chaining minimizes the number
of port pins required from the controlling IC (see Figure 28). The
SDO pin contains an open-drain N-Ch FET that requires a pull-up
resistor, if this function is used. As shown in Figure 28, users need
to tie the SDO pin of one package to the SDI pin of the next package.
Users may need to increase the clock period because the pull-up

Data Sheet ADN2850

CLK

R

P

2.2kΩ
SDI SDO

U2

CS

CLK

SDI SDO

U1

ADN2850

CS

V

DD

SCLK SS

MOSI

MICRO-

CONTROLLER

02660-040

ADN2850

V

SS

V

DD

W

B

02660-041

ADN2850

V

DD

GND

V

SS

C3

10µF

C4

10µFC20.1µF

C1

0.1µF

+

+

V

DD

V

SS

02660-042

resistor and the capacitive loading at the SDO-to-SDI interface may
require additional time delay between subsequent devices.

When two ADN2850s are daisy-chained, 48 bits of data are
required. The first 24 bits (formatted 4-bit command, 4-bit
address, and 16-bit data) go to U2, and the second 24 bits with
the same format go to U1. Keep
clocked into their respective serial registers.

EE

CS

AA

AA low until all 48 bits are

EE

CS

AA

AA is then pulled

high to complete the operation.

Figure 28. Daisy-Chain Configuration Using SDO

TERMINAL VOLTAGE OPERATING RANGE

The positive VDD and negative VSS power supplies of the ADN2850
define the boundary conditions for proper 2-terminal digital
resistor operation. Supply signals present on Termi na l B, and
Terminal W that exceed V
forward-biased diodes (see Figure 29).

or VSS are clamped by the internal

DD

extends from V

to VDD, regardless of the digital input level.

SS

Power-Up Sequence

Because there are diodes to limit the voltage compliance at
Terminal B, and Terminal W (see Figure 29), it is important to
power V

and VSS first before applying any voltage to Terminal

DD

B, and Terminal W. Otherwise, the diode is forward-biased such
that V
applying 5 V across Terminal W and Terminal B prior to V
causes the V

and VSS are powered unintentionally. For example,

DD

terminal to exhibit 4.3 V. It is not destructive to

DD

DD

the device, but it might affect the rest of the user’s system. The
ideal power-up sequence is GND, V
and V

, and VW. The order of powering VB, VW, and the digital

B

inputs is not important as long as they are powered after V
and V

.

SS

and VSS, digital inputs,

DD

DD

Regardless of the power-up sequence and the ramp rates of the
power supplies, when V

and VSS are powered, the power-on

DD

preset activates, which restores the EEMEM values to the RDAC
registers.

Layout and Power Supply Bypassing

It is a good practice to employ compact, minimum lead-length
layout design. The leads to the input should be as direct as
possible with a minimum conductor length. Ground paths
should have low resistance and low inductance.

Similarly, it is good practice to bypass the power supplies with
quality capacitors for optimum stability. Bypass supply leads to
the device with 0.01 µF to 0.1 µF disk or chip ceramic capacitors.
Also, apply low ESR, 1 µF to 10 µF tantalum or electrolytic
capacitors at the supplies to minimize any transient disturbance
(see Figure 30).

Figure 29. Maximum Terminal Voltages Set by V

DD

and V

SS

The GND pin of the ADN2850 is primarily used as a digital
ground reference. To minimize the digital ground bounce,
the ADN2850 ground terminal should be joined remotely to
the common ground (see Figure 30). The digital input control
signals to the ADN2850 must be referenced to the device
ground pin (GND) and must satisfy the logic level defined in
the Specifications section. An internal level-shift circuit ensures
that the common-mode voltage range of the three terminals

Figure 30. Power Supply Bypassing

Rev. E | Page 15 of 28

ADN2850 Data Sheet

MSB

Command Byte 0

Data Byte 1

Data Byte 0

LSB

Restore EEMEM (A0) contents to RDAC (A0)

Store wiper setting. Store RDAC (A0) setting to

Read RDAC wiper setting from SDO output in the

Write contents of Serial Register Data Byte 0 and

5

In Table 7, command bits are C0 to C3, address bits are A0 to A3, Data Bit D0 to Data Bit D9 are applicable to RDAC, and D0 to D15 are
applicable to EEMEM.

Table 7. 24-Bit Serial Data-Word

RDAC C3 C2 C1 C0 0 0 0 A0 X X X X X X D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
EEMEM

Command instruction codes are defined in Table 8.

Table 8. Command Operation Truth Table

Command
Number

0
1

2

320F4 0 0 1 1 A3 A2 A1 A0 D15 … D8 D7 … D0

5

4

21F

5

5

5

6

5

7

8

9

10

11

12

13

14

15

1

The SDO output shifts out the last 24 bits of data clocked into the serial register for daisy-chain operation. Exception: for any instruction following Instruction 9 or

Instruction 10, the selected internal register data is present in Data Byte 0 and Data Byte 1. The instructions following Instruction 9 and Instruction 10 must also be a
full 24-bit data-word to completely clock out the contents of the serial register.

2

The RDAC register is a volatile scratchpad register that is refreshed at power-on from the corresponding nonvolatile EEMEM register.

3

Execution of these operations takes place when the CS strobe returns to logic high.

4

Instruction 3 writes two data bytes (16 bits of data) to EEMEM. In the case of Address 0 and Address 1, only the last 10 bits are valid for wiper position setting.

5

The increment, decrement, and shift instructions ignore the contents of the shift register, Data Byte 0 and Data Byte 1.

C3 C2 C1 C0 A3 A2 A1 A0 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

1,

2,

3

17F

18F

19F

Command Byte 0 Data Byte 1 Data Byte 0

B23

B16 B15 B8 B7 B0

C2 C1 C0 A3 A2 A1 A0 X … D9 D8 D7 … D0

C3

0 0 0 0 X X X X X … X X X … X

Operation

NOP. Do nothing. See

Table 19

0 0 0 1 0 0 0 A0 X … X X X … X

register. See Table 16.

0 0 1 0 0 0 0 A0 X … X X X … X

EEMEM (A0). See Table 15.
Store contents of Serial Register Data Byte 0 and

Serial Register Data Bytes 1 (total 16 bits) to
EEMEM (ADDR). See Table 18.

0 1 0 0 0 0 0 A0 X … X X X … X

Decrement by 6 dB. Right-shift contents of RDAC
(A0) register, stop at all 0s.

0 1 0 1 X X X X X … X X X … X

Decrement all by 6 dB. Right-shift contents of all
RDAC registers, stop at all 0s.

0 1 1 0 0 0 0 A0 X … X X X … X

Decrement contents of RDAC (A0) by 1, stop at
all 0s.

0 1 1 1 X X X X X … X X X … X

Decrement contents of all RDAC registers by 1,
stop at all 0s.

1 0 0 0 0 0 0 0 X … X X X … X

Reset. Refresh all RDACs with their corresponding
EEMEM previously stored values.

1 0 0 1 A3 A2 A1 A0 X … X X X … X

Read contents of EEMEM (ADDR) from SDO
output in the next frame. See

1 0 1 0 0 0 0 A0 X … X X X … X

next frame. See Table 20.

1 0 1 1 0 0 0 A0 X … D9 D8 D7 … D0

Serial Register Data Byte 1 (total 10 bits) to RDAC

1 1 0 0 0 0 0 A0 X … X X X … X

5

1 1 0 1 X X X X X … X X X … X

(A0). See
Increment by 6 dB: Left-shift contents of RDAC (A0),
stop at all 1s. See
Increment all by 6 dB. Left-shift contents of all

Table 14.

Table 17.

RDAC registers, stop at all 1s.

5

1 1 1 0 0 0 0 A0 X … X X X … X

Increment contents of RDAC (A0) by 1, stop at all
1s. See Table 15.

5

1 1 1 1 X X X X X … X X X … X

Increment contents of all RDAC registers by 1,
stop at all 1s.

Table 19.

Rev. E | Page 16 of 28

Data Sheet ADN2850

00 0010 0000

00 0000 1111

11 1111 1111

00 0000 0000

CODE (From 1 to 1023 by 2.0 × 103)

0

GAIN (dB)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

0

–40

–20

–60

–80

02660-043

ADVANCED CONTROL MODES

The ADN2850 digital resistor includes a set of user
programming features to address the wide number of
applications for these universal adjustment devices.

Key programming features include the following:

• Scratchpad programming to any desirable values

• Nonvolatile memory storage of the scratchpad RDAC

register value in the EEMEM register

• Increment and decrement instructions for the RDAC wiper

register

• Left and right bit shift of the RDAC wiper register to

achieve ±6 dB level changes

• 26 extra bytes of user-addressable nonvolatile memory

Linear Increment and Decrement Instructions

The increment and decrement instructions (Instruction 14,
Instruction 15, Instruction 6, and Instruction 7) are useful for
linear step adjustment applications. These commands simplify
microcontroller software coding by allowing the controller to
send just an increment or decrement command to the device.
The adjustment can be individual or in a ganged resistor
arrangement where both wiper positions are changed at the
same time.

For an increment command, executing Instruction 14
automatically moves the wiper to the next resistance segment
position. The master increment command, Instruction 15,
moves all resistor wipers up by one position.

Logarithmic Taper Mode Adjustment

Four programming instructions produce logarithmic taper
increment and decrement of the wiper position control by
an individual resistor or by a ganged resistor arrangement
where both wiper positions are changed at the same time. The 6
dB increment is activated by Instruction 12 and Instruction 13,
and the 6 dB decrement is activated by Instruction 4 and
Instruction 5. For example, starting with the wiper connected to
Terminal B, executing 11 increment instructions (Command
Instruction 12) moves the wiper in 6 dB steps from 0% of the R
(Terminal B) position to 100% of the R

position of the

BA

ADN2850 10-bit resistor. When the wiper position is near the
maximum setting, the last 6 dB increment instruction causes
the wiper to go to the full-scale 1023 code position. Further 6
dB per increment instructions do not change the wiper position
beyond its full scale (see Tabl e 9).

The 6 dB step increments and 6 dB step decrements are achieved
by shifting the bit internally to the left or right, respectively. The
following information explains the nonideal ±6 dB step adjustment
under certain conditions. Table 9 illustrates the operation of the
shifting function on the RDAC register data bits. Each table row
represents a successive shift operation. Note that the left-shift
12 and 13 instructions were modified such that, if the data in
the RDAC register is equal to zero and the data is shifted left,

BA

the RDAC register is then set to Code 1. Similarly, if the data in
the RDAC register is greater than or equal to midscale and the data
is shifted left, then the data in the RDAC register is automatically
set to full scale. This makes the left-shift function as ideal a
logarithmic adjustment as possible.

The Right-Shift 4 instruction and Right-Shift 5 instruction are
ideal only if the LSB is 0 (ideal logarithmic = no error). If the
LSB is 1, the right-shift function generates a linear half-LSB
error, which translates to a number-of-bits dependent logarithmic
error, as shown in Figure 31. Figure 31 shows the error of the odd
numbers of bits for the ADN2850.

Table 9. Detail Left-Shift and Right-Shift Functions for 6 dB
Step Increment and Decrement

Left-Shift (+6 dB/Step) Right-Shift(–6 dB/Step)

00 0000 0000
00 0000 0001 01 1111 1111
00 0000 0010
00 0000 0100 00 0111 1111
00 0000 1000
00 0001 0000 00 0001 1111

00 0100 0000 00 0000 0111
00 1000 0000
01 0000 0000 00 0000 0001
10 0000 0000

11 1111 1111 00 0000 0000

11 1111 1111

00 1111 1111

00 0011 1111

00 0000 0011

00 0000 0000

Actual conformance to a logarithmic curve between the data
contents in the RDAC register and the wiper position for each
Right-Shift 4 command and Right-Shift 5 command execution
contains an error only for odd numbers of bits. Even numbers of
bits are ideal.

Figure 31 shows plots of log error [20 × log10
(error/code)] for the ADN2850. For example, Code 3 log error =
20 × log

(0.5/3) = −15.56 dB, which is the worst case. The log

10

error plot is more significant at the lower codes (see Figure 31).

Figure 31. Log Error Conformance for Odd Numbers of Bits Only

(Even Numbers of Bits Are Ideal)

Rev. E | Page 17 of 28

ADN2850 Data Sheet

SW

(1)

SW

(0)

SW

B

B

R

S

R

S

SW(2

N

–

1)

W

SW(2

N

–

2)

RDAC

WIPER

REGISTER

AND

DECODER

R

S

= R

WB_NOMINAL

/2

N

R

S

DIGITAL
CIRCUITRY
OMITTED FOR
CLARITY

02660-044

Using CS to Re-Execute a Previous Command

Another subtle feature of the ADN2850 is that a subsequent AA

CS

strobe, without clock and data, repeats a previous command.

Using Additional Internal Nonvolatile EEMEM

The ADN2850 contains additional user EEMEM registers for
storing any 16-bit data such as memory data for other components,
look-up tables, or system identification information. Table 10 pro­vides an address map of the internal storage registers shown in the
functional block diagram (see Figure 1) as EEMEM1, EEMEM2,
and 26 bytes (13 addresses × 2 bytes each) of User EEMEM.

Table 10. EEMEM Address Map

EEMEM No. Address EEMEM Content for …

1
2

0000 RDAC11

0001 RDAC2
3 0010 USER12
4

0011 USER2
… … …
15
16 1111 R

1

RDAC data stored in EEMEM locations is transferred to the corresponding

RDAC register at power-on, or when Instruction 1, Instruction 8, and
executed.

2

USERx are internal nonvolatile EEMEM registers available to store and

retrieve constants and other 16-bit information using Instruction 3 and
Instruction 9, respectively.

3

Read only.

1110 USER13

tolerance3

WB1

AA

PR

EE

AA are

Calculating Actual End-to-End Terminal Resistance

The resistance tolerance is stored in the EEMEM register during
factory testing. The actual end-to-end resistance can, therefore,
be calculated, which is valuable for calibration, tolerance matching,
and precision applications. Note that this value is read only and
the R

at full scale matches with R

WB2

at full scale, typically

WB1

0.1%.

The resistance tolerance in percentage is contained in the last
16 bits of data in EEMEM Register 15. The format is the sign
magnitude binary format with the MSB designate for sign
(0 = negative and 1 = positive), the next 7 MSB designate the
integer number, and the 8 LSB designate the decimal number
(see Table 12).

For example, if R

EE

AA

shows XXXX XXXX 1001 1100 0000 1111, R
be calculated as follows:

MSB: 1 = positive
Next 7 LSB: 001 1100 = 28
8 LSB: 0000 1111 = 15 × 2
% tolerance = 28.06%
Therefore, R

RDAC STRUCTURE

The RDAC contains multiple strings of equal resistor segments
with an array of analog switches that acts as the wiper
connection. The number of positions is the resolution of the device.
The ADN2850 has 1024 connection points, allowing it to provide
better than 0.1% setability resolution. Figure 32 shows an
equivalent structure of the connections among the three
terminals of the RDAC. The SW
switches, SW(0) to SW(2
the resistance position decoded from the data bits. Because the
switch is not ideal, there is a 30 Ω wiper resistance, R
resistance is a function of supply voltage and temperature. The
lower the supply voltage or the higher the temperature, the
higher the resulting wiper resistance. Users should be aware of
the wiper resistance dynamics, if accurate prediction of the
output resistance is needed.

Figure 32. Equivalent RDAC Structure

= 250 kΩ and the data in the SDO

WB_RAT ED

WB

−8

= 0.06

at full scale = 320.15 kΩ

WB

is always on, while the

N

B

− 1), are on one at a time, depending on

at full scale can

. Wiper

W

Table 11. Nominal Individual Segment Resistor Values

Table 12. Calculating End-to-End Terminal Resistance

Bit D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Sign
Mag

Sign 26 25 24 23 22 21 20
7 Bits for Integer Number

Rev. E | Page 18 of 28

Device Resolution 25 kΩ 250 kΩ

1024-Step

24.4Ω 244Ω

.

2−1 2−2 2−3 2−4 2−5 2−6 2−7 2−8

Decimal

Point

8 Bits for Decimal Number

Data Sheet ADN2850

CODE (Decimal)

100

75

0

0 1023256

R

WB

(D) (% R

WF

)

512 768

50

25

R

WB

02660-045

0

30

Zero scale (wiper contact resistor)

SDI

SDO

Action

PROGRAMMING THE VARIABLE RESISTOR

The nominal resistance of the RDAC between Terminal W and
Terminal B, R
1024 positions (10-bit resolution). The final digits of the part
number determine the nominal resistance value, for example,
25 kΩ = 24.4 Ω; 250 kΩ = 244 Ω.

The 10-bit data-word in the RDAC latch is decoded to select one of
the 1024 possible settings. The following description provides the
calculation of resistance, R
The first connection of the wiper starts at Terminal B for
Data 0x000. R
it is independent of the nominal resistance. The second connection
is the first tap point where R
for Data 0x001. The third connection is the next tap point
representing R
and so on. Each LSB data value increase moves the wiper up the
resistor ladder until the last tap point is reached at R
25006 Ω. See Figure 32 for a simplified diagram of the equivalent
RDAC circuit.

, is available with 25 kΩ and 250 kΩ with

WB

, at different codes of a 25 kΩ part.

WB

(0) is 30 Ω because of the wiper resistance, and

WB

(1) becomes 24.4 Ω + 30 Ω = 54.4 Ω

WB

(2) = 48.8 Ω + 30 Ω = 78.8 Ω for Data 0x002,

WB

(1023) =

WB

of 30 Ω is present. Care should be taken to limit the current
flow between W and B in this state to no more than 20 mA to
avoid degradation or possible destruction of the internal switches.

The typical distribution of R

from channel to channel is

WB_NOM

±0.2% within the same package. Device-to-device matching is
process lot dependent upon the worst case of ±30% variation.
However, the change in R

at full scale with temperature has a

WB

35 ppm/°C temperature coefficient.

PROGRAMMING EXAMPLES

The following programming examples illustrate a typical sequence
of events for various features of the ADN2850. See Table 8 for
the instructions and data-word format. The instruction numbers,
addresses, and data appearing at the SDI and SDO pins are in
hexadecimal format.

Table 14. Scratchpad Programming

SDI SDO Action

0xB00100

0xB10200

0xXXXXXX Writes Data 0x100 into RDAC1 register,

Wiper W1 moves to 1/4 full-scale
position.

0xB00100 Loads Data 0x200 into RDAC2 register,

Wiper W2 moves to 1/2 full-scale
position.

Table 15. Incrementing RDAC Followed by Storing the
Wiper Setting to EEMEM

0xB00100 0xXXXXXX Writes Data 0x100 into RDAC1

register, Wiper W1 moves to 1/4 full­scale position.

0xE0XXXX

0xB00100 Increments RDAC1 register by one to

0x101.

0xE0XXXX

0xE0XXXX Increments RDAC1 register by one to

0x102. Continue until desired wiper
position is reached.

EEMEM1. Optionally, tie

EE

AA

AA to GND to

WP

protect EEMEM values.

EE

PR

AA

AA pin, or by the two commands shown in

Figure 33. R

(D) vs. Decimal Code

WB

The general equation that determines the programmed output
resistance between Terminal Bx and Terminal Wx is

)(

DR +×=

D

1024

_

(1)

RR

WNOMWBWB

0x20XXXX

0xXXXXXX Stores RDAC2 register data into

The EEMEM values for the RDACs can be restored by power­on, by strobing the
Table 16.

where:

Table 16. Restoring the EEMEM Values to RDAC Registers

SDI SDO Action

0x10XXXX

0xXXXXXX Restores the EEMEM1 value to the

RDAC1 register.

D is the decimal equivalent of the data contained in the RDAC
register.

R

is the nominal resistance value

WB_NOM

R

is the wiper resistance.

W

Table 13. R

(D) at Selected Codes for R

WB

= 25 kΩ

WB_NOM

D (Dec) RWB(D) (Ω) Output State

1023

25,006 Full scale
512 12,530 Midscale
1

54.4 1 LSB

Note that, in the zero-scale condition, a finite wiper resistance

Rev. E | Page 19 of 28

ADN2850 Data Sheet

Table 17. Using Left-Shift by One to Increment 6 dB Steps

SDI SDO Action

0xC0XXXX

0xC1XXXX

0xXXXXXX Moves Wiper 1 to double the

present data contained in the
RDAC1 register.

0xC0XXXX Moves Wiper 2 to double the

present data contained in the
RDAC2 register.

Table 19. Reading Back Data from Memory Locations

SDI SDO Action

0x92XXXX

0x00XXXX 0x92AAAA NOP Instruction 0 sends a 24-bit word

0xXXXXXX Prepares data read from USER1

EEMEM location.

out of SDO, where the last 16 bits
contain the contents in USER1 EEMEM
location.

Table 18. Storing Additional User Data in EEMEM

SDI SDO Action

0x32AAAA

0x335555

0xXXXXXX Stores Data 0xAAAA in the extra

EEMEM location USER1. (Allowable to
address in 13 locations with a
maximum of 16 bits of data.)

0x32AAAA Stores Data 0x5555 in the extra

EEMEM location USER2. (Allowable to
address in 13 locations with a
maximum of 16 bits of data.)

Table 20. Reading Back Wiper Settings

SDI SDO Action

0xB00200
0xC0XXXX 0xB00200 Doubles RDAC1 from midscale to full

0xA0XXXX 0xC0XXXX Prepares reading wiper setting from

0xXXXXXX 0xA003FF Reads back full-scale value from SDO.

0xXXXXXX Writes RDAC1 to midscale.

scale.

RDAC1 register.

EVAL-ADN2850SDZ EVALUATION KIT

Analog Devices, Inc., offers a user-friendly EVA L­ADN2850SDZ evaluation kit that can be controlled by a PC in
conjunction with the DSP platform. The driving program is
self-contained; no programming languages or skills are needed.

Rev. E | Page 20 of 28

Data Sheet ADN2850

U1

V

O

R2

250kΩ

V

I

R1

47kΩ

C1

11pF

W

B

C2

2.2pF

02660-047

B

V

I

AD8601

+2.5V

V

O

ADJUSTED

CONCURRENTLY

–2.5V

V+

V–

W

R

R2R1

B

W

R

C1

C2

U1

02660-055

C2C1R2R1

O

1

=ω

C2R2

1

C1R1

+

1

D1

D2

OP1177

V+

V–

+2.5V

+

–

–2.5V

V

O

U1

R2A

2.1kΩ

R2B

10kΩ

B A

W

R1
1kΩ

AMPLITUDE

ADJUSTMENT

R = R' = ADN2850
R2B = AD5231
D1 = D2 = 1N4148

R'

25kΩ

A

B

W

C'

VP

R

25kΩ

B

W

C

2.2nF

FREQUENCY

ADJUSTMENT

2.2nF

02660-056

APPLICATIONS INFORMATION

GAIN CONTROL COMPENSATION

A digital resistor is commonly used in gain control such as the
noninverting gain amplifier shown in Figure 34.

Figure 34. Typical Noninverting Gain Amplifier

When the RDAC B terminal parasitic capacitance is connected
to the op amp noninverting node, it introduces a zero for the 1/β
term with 20 dB/dec, whereas a typical op amp gain bandwidth
product (GBP) has −20 dB/dec characteristics. A large R2 and
finite C1 can cause the frequency of this zero to fall well below
the crossover frequency. Therefore, the rate of closure becomes
40 dB/dec, and the system has a 0° phase margin at the crossover
frequency. If an input is a rectangular pulse or step function, the
output can ring or oscillate. Similarly, it is also likely to ring when
switching between two gain values; this is equivalent to a stop
change at the input.

Depending on the op amp GBP, reducing the feedback resistor
might extend the frequency of the zero far enough to overcome
the problem. A better approach is to include a compensation
capacitor, C2, to cancel the effect caused by C1. Optimum
compensation occurs when R1 × C1 = R2 × C2. This is not
an option because of the variation of R2. As a result, one can
use the previous relationship and scale C2 as if R2 were at its
maximum value. Doing this might overcompensate and
compromise the performance when R2 is set at low values.

Alternatively, it avoids the ringing or oscillation at the worst
case. For critical applications, find C2 empirically to suit the
oscillation. In general, C2 in the range of a few picofarads to no
more than a few tenths of picofarads is usually adequate for the
compensation.

Similarly, W and A terminal capacitances are connected to the
output (not shown); their effect at this node is less significant
and the compensation can be avoided in most cases.

PROGRAMMABLE LOW-PASS FILTER

In analog-to-digital conversions (ADCs), it is common to
include an antialiasing filter to band limit the sampling signal.
Therefore, the dual-channel ADN2850 can be used to construct
a second-order Sallen-Key low-pass filter, as shown in Figure 35.

The design equations are

O

First, users should select convenient values for the capacitors.
To achieve maximally flat bandwidth, where Q = 0.707, let C1
be twice the size of C2 and let R1 equal R2. As a result, the user
can adjust R1 and R2 concurrently to the same setting to
achieve the desirable bandwidth.

PROGRAMMABLE OSCILLATOR

In a classic Wien bridge oscillator, the Wien network (R||C, R'C')
provides positive feedback, whereas R1 and R2 provide negative
feedback (see Figure 36).

Rev. E | Page 21 of 28

Figure 35. Sallen-Key Low-Pass Filter

2

V

O

=

V

I

ω

f

ω

f

2

S

S

+

Q

(10)

2

ω+

f

(11)

Q =

Figure 36. Programmable Oscillator with Amplitude Control

(12)

ADN2850 Data Sheet

RC

O

1

=ω

RC

f

O

π=2

1

WNOMWBWB

RR

D

DR +×=

_

1024

)(

DDO

VIV += R2B

3

2

CS

CLK

SDI

W1

B1

EEMEM

ADN2841

PSET

ERSET

IMODP

IBIAS

IMPD

DATAP

DATAN

CLKP

CLKN

CLKN

CLKP
DATAP
DATAN

W2

B2

EEMEM

CONTROL

ADN2850

V

CC

V

CC

RDAC1

RDAC2

02660-057

1

1

11

ln

S

C

TBE

I

I

VVV ==

2

S

I

V

PD

REF

T

I

I

VVV ln

12

=−

At the resonant frequency, fO, the overall phase shift is zero, and
the positive feedback causes the circuit to oscillate. With R = R

C = C

', and R2 = R2A /(R2B + R

), the oscillation frequency is

DIODE

',

or

where R is equal to R

WA

(13)

such that :

(14)

At resonance, setting R2/R1 = 2 balances the bridge. In practice,
R2/R1 should be set slightly larger than 2 to ensure that the
oscillation can start. On the other hand, the alternate turn-on
of the diodes, D1 and D2, ensures that R2/R1 is smaller than 2,
momentarily stabilizing the oscillation.

When the frequency is set, the oscillation amplitude can be
turned by R2B because

(15)

V

, ID, and VD are interdependent variables. With proper

O

selection of R2B, an equilibrium is reached such that V
converges. R2B can be in series with a discrete resistor to
increase the amplitude, but the total resistance cannot be too
large to saturate the output.

In Figure 35 and Figure 36, the frequency tuning requires that
both RDACs be adjusted concurrently to the same settings.
Because the two channels might be adjusted one at a time, an
intermediate state occurs that might not be acceptable for some
applications. Of course, the increment/decrement instructions
(Instruction 5, Instruction 7, Instruction 13, and Instruction 15)
can all be used. Different devices can also be used in daisy-chain
mode so that parts can be programmed to the same settings
simultaneously.

OPTICAL TRANSMITTER CALIBRATION WITH ADN2841

The ADN2850, together with the multirate 2.7 Gbps laser diode
driver, ADN2841, forms an optical supervisory system in which
the dual digital resistor can be used to set the laser average optical
power and extinction ratio (see Figure 37). The ADN2850 is
particularly suited for the optical parameter settings because of
its high resolution and superior temperature coefficient
characteristics.

Figure 37. Optical Supervisory System

The ADN2841 is a 2.7 Gbps laser diode driver that uses a
unique control algorithm to manage the average power and
extinction ratio of the laser after its initial factory calibration.
The ADN2841 stabilizes the data transmission of the laser by
continuously monitoring its optical power and correcting the

O

variations caused by temperature and the degradation of the
laser over time. In the ADN2841, the IMPD monitors the laser
diode current. Through its dual-loop power and extinction
ratio control calibrated by the dual RDACs of the ADN2850, the
internal driver controls the bias current, IBIAS, and consequently
the average power. It also regulates the modulation current,
IMODP, by changing the modulation current linearly with slope
efficiency. Therefore, any changes in the laser threshold current or
slope efficiency are compensated for. As a result, the optical
supervisory system minimizes the laser characterization efforts
and, therefore, enables designers to apply comparable lasers
from multiple sources.

INCOMING OPTICAL POWER MONITORING

The ADN2850 comes with a pair of matched diode connected
PNPs, Q1 and Q2, that can be used to configure an incoming
optical power monitoring function. With a reference current
source, an instrumentation amplifier, this feature can be used to
monitor the optical power by knowing the dc average photodiode
current from the following relationships:

(16)

VV

==

22

Knowing I
therefore α and I

= α1 × IPD, IC2 = α2 x I

C1

are matched. Combining Equation 16 and

S

Equation 17 theoretically yields:

Rev. E | Page 22 of 28

2

C

(17)

ln

TBE

I

, and Q1-Q2 are matched,

REF

(18)

Data Sheet ADN2850

where:

and IS2 are saturation current.

I

S1

V

, V2 are VBE, base-emitted voltages of the diode connector

1

transistors.
V

is the thermal voltage, which is equal to k × T/q

T

= 26 mV @ 25°C)

(V

T

k is the Boltzmann’s constant, 1.38e-23 Joules/Kelvin.
q is the electron charge, 1.6e-19 coulomb.
T is the temperature in Kelvin.
I

is the photodiode current.

PD

I

is the reference current.

REF

Figure 38 shows a conceptual circuit.

POST

AMP

CDR

VT COMPENSATION

°C
PRC
THERMISTOR

ADN2850

W

V

DD

LPF

TIA

Q

R

G

V

2

2

0.75 BIT RATE

AD623

IN AMP

(1 + 100k/RG)×(V1–V2)

10nF

I

PDIREF

W2V

1

1

Q

1

DATA
CLOCK

LOG
AVERAGE
POWER

0.30

0.25

0.20

(V)

1

0.15

–V

2

V

0.10

0.05

0

0.1µ 1µ 10µ 100µ 1m

Figure 39. V

DEVICE 1
DEVICE 2
DEVICE 3
CURVE FIT

IPD(A)

– V1 Error Versus Input Current.

2

I
T

REF

= 25°C

A

=1mA

ERROR

12

9

6

3

0

APPROXIMATING ERROR (%)

–3

–6

RESISTANCE SCALING

The ADN2850 offers 25 kΩ or 250 kΩ nominal resistance.
When users need lower resistance but must maintain the
number of adjustment steps, they can parallel multiple devices. For
example, Figure 40 shows a simple scheme of paralleling two
channels of RDACs. To adjust half the resistance linearly per
step, program both RDACs concurrently with the same settings.

02660-138

V

SS

B

B

1

2

GND

LOG AMP

–5V

Figure 38. Conceptual Incoming Optical Power Monitoring Circuit

The output voltage represents the average incoming optical
power. The output voltage of the log stage does not have to be
accurate from device to device, as the responsivity of the
photodiode will change between devices. An op amp stage is
shown after the log amp stage, which compensates for V

T

variation over temperature.

Equation 19 is ideal. If the reference current is 1 mA at room
temperature, characterization shows that there is an additional
30 mV offset between V

and V1. A curve fit approximation

2

yields

VV

12

001.0

ln026.0

I

PD

03.0



(19)

The offset is caused by the transistors self-heating and the
thermal gradient effect. As seen in Figure 39, the error between
an approximation and the actual performance ranges is less
than 0% to –4% from 0.1 mA to 0.1 μA.

W1

02660-137

B1

B2

W2

02660-058

Figure 40. Reduce Resistance by Half with Linear Adjustment Characteristics

Figure 40 shows that the digital rheostat change steps linearly.
Alternatively, pseudo log taper adjustment is usually preferred in
applications such as audio control. Figure 41 shows another type
of resistance scaling. In this configuration, the smaller the R2
with respect to R

, the more the pseudo log taper characteristic

AB

of the circuit behaves.

W1

B1

R

02660-060

Figure 41. Resistor Scaling with Pseudo Log Adjustment Characteristics

The equation is approximated as

R



R

QUIVALENT

E



WB

WB

200,51

1024200,51

(17)

RR



Users should also be aware of the need for tolerance matching
as well as for temperature coefficient matching of the components.

Rev. E | Page 23 of 28

ADN2850 Data Sheet

AD8601

+

–

V

i

U1

V

O

C1

B

W

R2

R1*

*REPLACED WITH ANOTHER

CHANNEL OF RDAC

02660-061

RDAC

25kΩ

W

80pF

C

B

11pF

B

02660-063

RESISTANCE TOLERANCE, DRIFT, AND TEMPERATURE COEFFICIENT MISMATCH CONSIDERATIONS

In operation, such as gain control, the tolerance mismatch
between the digital resistor and the discrete resistor can cause
repeatability issues among various systems (see Figure 42).
Because of the inherent matching of the silicon process, it is
practical to apply the dual-channel device in this type of
application. As such, R1 can be replaced by one of the channels
of the digital resistor and programmed to a specific value. R2 can
be used for the adjustable gain. Although it adds cost, this approach
minimizes the tolerance and temperature coefficient mismatch
between R1 and R2. This approach also tracks the resistance
drift over time. As a result, these less than ideal parameters
become less sensitive to system variations.

Figure 42. Linear Gain Control with Tracking Resistance Tolerance,

Drift, and Temperature Coefficient

RDAC CIRCUIT SIMULATION MODEL

The internal parasitic capacitances and the external capacitive
loads dominate the ac characteristics of the RDACs. A parasitic
simulation model is shown in Figure 43.

Figure 43. RDAC Circuit Simulation Model (RDAC = 25 kΩ)

The following code provides a macro model net list for the
25 kΩ RDAC:

.PARAM D = 1024, RDAC = 25E3
*
.SUBCKT DPOT ( W, B)
*
CW W 0 80E-12
RWB W B {D/1024 * RDAC + 50}
CB B 0 11E-12
*
.ENDS DPOT

Rev. E | Page 24 of 28

Data Sheet ADN2850

COMPLIANT

TO

JEDEC STANDARDS MO-220-VGGC

05-09-2012-A

1

0.80
BSC

PIN 1
INDICATOR

2.40 REF

0.75

0.60

0.50

TOP VIEW

12° MAX

0.80 MAX

0.65 TYP

SEATING

PLANE

COPLANARITY

0.08

1.00

0.85

0.80

0.35

0.30

0.25

0.05 MAX

0.02 NOM

0.20 REF

3.25

3.10 SQ

2.95

16

5

13

8

9

12

4

0.60 MAX

0.60 MAX

PIN 1

INDICATOR

5.10

5.00 SQ

4.90

4.75 BSC
SQ

EXPOSED

PAD

FOR PROP E R CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CO NFIGURATI ON AND
FUNCTIO N DE S CRIPTIONS
SECTION OF THIS DATA SHEET.

0.25 MIN

BOTTOM VIEW

16

9

81

PIN 1

SEATING
PLANE

8°
0°

4.50

4.40

4.30

6.40
BSC

5.10

5.00

4.90

0.65

BSC

0.15

0.05

1.20
MAX

0.20

0.09

0.75

0.60

0.45

0.30

0.19

COPLANARITY

0.10

COMPLI ANT TO JEDEC STANDARDS MO-153-AB

OUTLINE DIMENSIONS

Figure 44. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ]

5 × 5 mm Body, Very Thin Quad

(CP-16-6)

Dimensions shown in millimeters

Figure 45. 16-Lead Thin Shrink Small Outline Package [TSSOP]

(RU-16)

Dimensions shown in millimeters

ORDERING GUIDE

1, 2

Model

ADN2850BRUZ25 25 −40°C to +85°C 16-Lead TSSOP RU-16
ADN2850BRUZ25-RL7 25 −40°C to +85°C 16-Lead TSSOP RU-16
ADN2850BCPZ25 25 −40°C to +85°C 16-Lead LFCSP_VQ CP-16-6
ADN2850BCPZ25-RL7 25 −40°C to +85°C 16-Lead LFCSP_VQ CP-16-6
ADN2850BCPZ250 250 −40°C to +85°C 16-Lead LFCSP_VQ CP-16-6
ADN2850BCPZ250-RL7 250 −40°C to +85°C 16-Lead LFCSP_VQ CP-16-6
EVAL-ADN2850SDZ Evaluation Board

1

Z = RoHS Compliant Part.

2

The evaluation board is shipped with the 25 kΩ RWB resistor option; however, the board is compatible with all available resistor value options.

RWB (kΩ) Temperature Range Package Description Package Option

Rev. E | Page 25 of 28

ADN2850 Data Sheet

NOTES

Rev. E | Page 26 of 28

Data Sheet ADN2850

NOTES

Rev. E | Page 27 of 28

ADN2850 Data Sheet

©2004–2012 Analog Devices, Inc. All rights reserved. Trademarks and

NOTES

registered trademarks are the property of their respective owners.
D02660-0-6/12(E)

Rev. E | Page 28 of 28