ANALOG DEVICES AD7356 Service Manual

Differential Input, Dual, Simultaneous

A

V

V

www.BDTIC.com/ADI

FEATURES

Dual 12-bit SAR ADC
Simultaneous sampling
Throughput rate: 5 MSPS per channel
Specified for V
No conversion latency
Power dissipation: 36 mW at 5 MSPS
On-chip reference: 2.048 V ± 0.25%, 6 ppm/°C
Dual conversion with read
High speed serial interface: SPI-/QSPI™-/MICROWIRE™-/DSP-

compatible

−40°C to +125°C operation
Available in a 16-lead TSSOP

at 2.5 V

DD

Sampling, 5 MSPS, 12-Bit, SAR ADC

AD7356

FUNCTIONAL BLOCK DIAGRAM

DRIVE

12-BIT

SUCCESSIVE

APPROXIMATION

ADC

CONTROL

LOGIC

12-BIT

SUCCESSIVE

APPROXIMATION

ADC

Figure 1.

AD7356

SDATA

SCLK

CS

SDATA

06505-001

DGNDREFGNDAGND

V
V
REF

REF
V
V

INA+

INA–

INB+

INB–

DD

T/H

A

BUF

REF

BUF

B

T/H

AGND

B

GENERAL DESCRIPTION

The AD73561 is a dual, 12-bit, high speed, low power, successive
approximation ADC that operates from a single 2.5 V power
supply and features throughput rates up to 5 MSPS. The part
contains two ADCs, each preceded by a low noise, wide band­width track-and-hold circuit that can handle input frequencies
in excess of 110 MHz.

The conversion process and data acquisition use standard
control inputs allowing for easy interfacing to microprocessors
or DSPs. The input signal is sampled on the falling edge of
a conversion is also initiated at this point. The conversion time
is determined by the SCLK frequency.

The AD7356 uses advanced design techniques to achieve very
low power dissipation at high throughput rates. With a 2.5 V
supply and a 5 MSPS throughput rate, the part consumes typically
14 mA. The part also offers a flexible power/throughput rate
management option.

The analog input range for the part is the differential common
mode ±V

/2. The AD7356 has an on-chip 2.048 V reference

REF

that can be overdriven when an external reference is preferred.

The AD7356 is available in a 16-lead thin shrink small outline
package (TSSOP).

CS

;

PRODUCT HIGHLIGHTS

1. Two Complete A D C Fu nc tions.

These functions allow simultaneous sampling and
conversion of two channels. The conversion result of both
channels is simultaneously available on separate data lines
or in succession on one data line if only one serial port is
available.

2. High Throughput with Low Power Consumption.

The AD7356 offers a 5 MSPS throughput rate with 36 mW
power consumption.

3. No Conversion Latency.

The AD7356 features two standard successive approx­imation ADCs with accurate control of the sampling
instant via a

Table 1. Related Devices

Generic Resolution Throughput Analog Input

AD7352 12-bit 3 MSPS Differential
AD7266 12-bit 2 MSPS Differential/single ended
AD7866 12-bit 1 MSPS Single-ended
AD7366 12-bit 1 MSPS Single-ended bipolar
AD7367 14-bit 1 MSPS Single-ended bipolar

CS

input and, once off, conversion control.

1

Protected by U.S. Patent No. 6,681,332.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of p atents 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.
Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2008 Analog Devices, Inc. All rights reserved.

AD7356

www.BDTIC.com/ADI

TABLE OF CONTENTS

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

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

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

Product Highlights ........................................................................... 1

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

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

Timing Specifications .................................................................. 5

Absolute Maximum Ratings ............................................................ 6

ESD Caution .................................................................................. 6

Pin Configuration and Function Descriptions ............................. 7

Typical Performance Characteristics ............................................. 8

Terminology .................................................................................... 10

Theory of Operation ...................................................................... 12

Circuit Information .................................................................... 12

Converter Operation .................................................................. 12

Analog Input Structure .............................................................. 12

Analog Inputs ............................................................................. 13

Driving Differential Inputs ....................................................... 14

ADC Transfer Function ............................................................. 14

Modes of Operation ....................................................................... 15

Normal Mode .............................................................................. 15

Partial Power-Down Mode ....................................................... 15

Full Power-Down Mode ............................................................ 16

Power-Up Times ......................................................................... 17

Power vs. Throughput Rate ....................................................... 17

Serial Interface ................................................................................ 18

Application Hints ........................................................................... 19

Grounding and Layout .............................................................. 19

Evaluating the AD7356 Performance ...................................... 19

Outline Dimensions ....................................................................... 20

Ordering Guide .......................................................................... 20

REVISION HISTORY

10/08—Revision 0: Initial Version

Rev. 0 | Page 2 of 20

AD7356

www.BDTIC.com/ADI

SPECIFICATIONS

IN+

MAX

and

IN+

and V

1

, unless

are

IN−

VDD = 2.5 V ± 10%, V

= 2.25 V to 3.6 V, internal reference = 2.048 V, f

DRIVE

= 80 MHz, f

SCLK

= 5 MSPS, TA = T

SAMPLE

MIN

to T

otherwise noted.

Table 2.

Parameter Min Typ Max Unit Test Conditions/Comments

DYNAMIC PERFORMANCE fIN = 1 MHz sine wave

Signal-to-Noise Ratio (SNR)
Signal-to-(Noise and Distortion) (SINAD)
Total Harmonic Distortion (THD)
Spurious Free Dynamic Range (SFDR)
Intermodulation Distortion (IMD)

Second-Order Terms −84 dB
Third-Order Terms −76 dB

ADC-to-ADC Isolation

2

CMRR

SAMPLE AND HOLD

Aperture Delay 3.5 ns
Aperture Delay Match 40 ps
Aperture Jitter 16 ps
Full Power Bandwidth

@ 3 dB 110 MHz
@ 0.1 dB 77 MHz

DC ACCURACY

Resolution 12 Bits
Integral Nonlinearity (INL)
Differential Nonlinearity (DNL)
Positive Full-Scale Error
Positive Full-Scale Error Match
Midscale Error

2

Midscale Error Match
Negative Full-Scale Error
Negative Full-Scale Error Match

ANALOG INPUT

Fully Differential Input Range (V

Common-Mode Voltage Range 0.5 1.9 V The voltage around which V

DC Leakage Current ±0.5 ±5 A
Input Capacitance 32 pF When in track mode
8 pF When in hold mode

REFERENCE INPUT/OUTPUT

V

Input Voltage Range 2.048 + 0.1 VDD V

REF

V

Input Current 0.3 0.45 mA When in reference overdrive mode

REF

V

Output Voltage 2.038 2.058 V 2.048 V ± 0.5% max @ VDD = 2.5 V ± 5%

REF

2.043 2.053 V 2.048 V ± 0.25% max @ VDD = 2.5 V ± 5% and 25°C
V

Temperature Coefficient 6 20 ppm/°C

REF

V

Long Term Stability 100 ppm For 1000 hours

REF

V

Thermal Hysteresis

REF

V

Noise 60 V rms

REF

V

Output Impedance 1 Ω

REF

2

2

2

2

2

2

2

2

2

70 71.5 dB

2

69.5 71 dB

−84 −77.5 dB

−85 −78.5 dB
fa = 1 MHz + 50 kHz, fb = 1 MHz − 50 KHz

−100 dB fIN = 1 MHz, f

−100 dB f

= 100 kHz to 2.5 MHz

NOISE

= 100 kHz to 2.5 MHz

NOISE

±0.5 ±1 LSB
±0.5 ±0.99 LSB Guaranteed no missed codes to 12 bits
±1 ±6 LSB
±2 ±8 LSB
+5 0/+11 LSB

2

2

2

and V

IN+

±2 ±8 LSB
±1 ±6 LSB
±2 ±8 LSB

) VCM ± V

IN−

/2 V VCM = common-mode voltage, V

REF

must remain within GND and VDD

V

IN−

centered

2

50 ppm

Rev. 0 | Page 3 of 20

AD7356

www.BDTIC.com/ADI

Parameter Min Typ Max Unit Test Conditions/Comments

LOGIC INPUTS

Input High Voltage (V
Input Low Voltage (V
Input Current (I
Input Capacitance (CIN) 3 pF

LOGIC OUTPUTS

Output High Voltage (VOH) V
Output Low Voltage (VOL) 0.2 V
Floating-State Leakage Current ±1 A
Floating-State Output Capacitance 5.5 pF
Output Coding Straight binary

CONVERSION RATE

Conversion Time t2 + 13 × t
Track-and-Hold Acquisition Time
Throughput Rate 5 MSPS

POWER REQUIREMENTS

VDD 2.25 2.75 V Nominal VDD = 2.5 V
V

2.25 3.6 V

DRIVE

4

I

TOTAL

Normal Mode (Operational) 14 20 mA
Normal Mode (Static) 6 7.8 mA SCLK on or off
Partial Power-Down Mode 3.5 4.5 mA SCLK on or off
Full Power-Down Mode 5 40 A SCLK on or off, −40°C to +85°C
90 A SCLK on or off, 85°C to 125°C

Power Dissipation

Normal Mode (Operational) 36 59 mW
Normal Mode (Static) 16 21.5 mW SCLK on or off
Partial Power-Down Mode 9.5 11.5 mW SCLK on or off
Full Power-Down Mode 16 110 W SCLK on or off, −40°C to +85°C
250 W SCLK on or off, 85°C to 125°C

1

Temperature ranges are as follows: Y Grade: −40°C to +125°C; B Grade: −40°C to +85°C.

2

See the Terminology section.

3

Current and power typical specifications are based on results with VDD = 2.5 V and V

4

I

is the total current flowing in VDD and V

TOTAL

) 0.6 × V

INH

) 0.3 × V

INL

) ±1 A VIN = 0 V or V

IN)

2

3

30 ns Full-scale step input, settling to 0.5 LSBs

V

DRIVE

V

DRIVE

− 0.2 V

DRIVE

ns

SCLK

Digital inputs = 0 V or V

= 3.0 V.

DRIVE

.

DRIVE

DRIVE

DRIVE

Rev. 0 | Page 4 of 20

AD7356

www.BDTIC.com/ADI

TIMING SPECIFICATIONS

VDD = 2.5 V ± 10%, V

= 2.25 V to 3.6 V, internal reference = 2.048 V, TA = T

DRIVE

MAX

Table 3.

Parameter Limit at T

f

SCLK

50 kHz min

MIN

, T

MAX

Unit Description

80 MHz max
t

CONVER T

t

5 ns min

QUIET

t

2

2

t

3

2, 3

t

4

12.5 ns max 1.8 V ≤ V
11 ns max 2.25 V ≤ V

9.5 ns max 2.75 V ≤ V
9 ns max 3.3 V ≤ V

t2 + 13 × t

ns max t

SCLK

SCLK

= 1/f

SCLK

Minimum time between end of serial read and next falling edge of CS
5 ns min
6 ns max

to SCLK setup time

CS

Delay from CS

until SDATAA and SDATAB are three-state disabled

Data access time after SCLK falling edge

< 2.25 V

DRIVE

< 2.75 V

DRIVE

< 3.3 V

DRIVE

≤ 3.6 V

DRIVE

t5 5 ns min SCLK low pulse width
t6 5 ns min SCLK high pulse width

2

t

3.5 ns min SCLK to data valid hold time

7

2

t

9.5 ns max

8

t9 5 ns min

2

t

4.5 ns min SCLK falling edge to SDATA

10

rising edge to SDATA , SDATAB high impedance

CS

rising edge to falling edge pulse width

CS

9.5 ns max SCLK falling edge to SDATAA, SDATAB high impedance

1

Temperature ranges are as follows: Y Grade: −40°C to +125°C; B Grade: −40°C to +85°C.

2

Specified with a load capacitance of 10 pF on SDATAA and SDATAB.

3

The time required for the output to cross 0.4 V or 2.4 V.

1

to T

, unless otherwise noted.

MIN

A

, SDATAB high impedance

A

Rev. 0 | Page 5 of 20

AD7356

www.BDTIC.com/ADI

ABSOLUTE MAXIMUM RATINGS

Table 4.

Parameter Rating

VDD to AGND, DGND, REFGND

V

to AGND, DGND, REFGND −0.3 V to +5 V

DRIVE

VDD to V
AGND to DGND to REFGND

Analog Input Voltages1 to AGND

Digital Input Voltages2 to DGND −0.3 V to V
Digital Output Voltages3 to DGND

Input Current to Any Pin Except Supply Pins4 ±10 mA
Operating Temperature Range

Y Grade

B Grade

Storage Temperature Range

Junction Temperature 150°C
TSSOP

θJA Thermal Impedance 143°C/W
θJC Thermal Impedance 45°C/W

Lead Temperature, Soldering

Reflow Temperature (10 sec to 30 sec) 255°C

ESD 1.5 kV

1

Analog input voltages are V

2

Digital input voltages are CS and SCLK.

3

Digital output voltages are SDATAA and SDATAB.

4

Transient currents of up to 100 mA do not cause SCR latch-up.

−5 V to +3 V

DRIVE

, V

, V

INA−

INB+

, V

INA+

−0.3 V to +3 V

−0.3 V to +0.3 V

−0.3 V to V

−0.3 V to V

−40°C to +125°C

−40°C to +85°C

−65°C to +150°C

, REFA, and REFB.

INB−

+ 0.3 V

DD

+ 0.3 V

DRIVE

+ 0.3 V

DRIVE

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. 0 | Page 6 of 20