Rainbow Electronics MAX1089 User Manual

Page 1

General Description

The MAX1086–MAX1089 are low-cost, micropower, serial output 10-bit analog-to-digital converters (ADCs) available in a tiny 8-pin SOT23. The MAX1086/MAX1088 operate with a single +5V supply. The MAX1087/MAX1089 operate with a single +3V supply. The devices feature a successive-approximation ADC, automatic shutdown, fast wake-up (1.4µs), and a high-speed 3-wire interface. Power consumption is only 0.5mW (VDD= +2.7V) at the maximum sampling rate of 150ksps. Autoshutdown™ (0.1µA) between conversions results in reduced power consumption at slower throughput rates.

The MAX1086/MAX1087 provide 2-channel, singleended operation and accept input signals from 0 to V

REF

. The MAX1088/MAX1089 accept true-differential

inputs ranging from 0 to V

REF

. Data is accessed using an external clock through the 3-wire SPI™, QSPI™, and MICROWIRE™–compatible serial interface. Excellent dynamic performance, low-power, ease of use, and small package size, make these converters ideal for portable battery-powered data acquisition applications, and for other applications that demand low power consumption and minimal space.

Applications

Low Power Data Acquisition

Portable Temperature Monitors

Flowmeters

Touch Screens

Features

♦ Single-Supply Operation

+3V(MAX1087/MAX1089) +5V(MAX1086/MAX1088)

♦ AutoShutdown Between Conversions

♦ Low Power

200µA at 150ksps 130µA at 100ksps 65µA at 50ksps 13µA at 10ksps

1.5µA at 1ksps

0.2µA in Shutdown

♦ True-Differential Track/Hold, 150kHz Sampling Rate

♦ Software-Configurable Unipolar/Bipolar

Conversion (MAX1088/MAX1089 only)

♦ SPI, QSPI, MICROWIRE–Compatible Interface for

DSPs and Processors

♦ Internal Conversion Clock

♦ 8-Pin SOT23 Package

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

19-2036; Rev 0; 5/01

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

AutoShutdown is a trademark of Maxim Integrated Products. SPI and QSPI are trademarks of Motorola Inc. MICROWIRE is a trademark of National Semiconductor Corp.

PART

MAX1086EKA-T -40°C to +85°C 8 SOT23 AAEZ

MAX1087EKA-T -40°C to +85°C 8 SOT23 AAEV

MAX1088EKA-T -40°C to +85°C 8 SOT23 AAFB

MAX1089EKA-T -40°C to +85°C 8 SOT23 AAEX

TEMP.

RANGE

PIN-

PACKAGE

TOP

MARK

TOP VIEW

MAX1086 MAX1087

AIN2 (AIN-)

( ) ARE FOR THE MAX1088/MAX1089

MAX1088 MAX1089

SOT23-8

87SCLK

DOUTAIN1 (AIN+)

CNVST

REFGND

Page 2

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= +2.7V to +3.6V, V

REF

= +2.5V for MAX1087/MAX1089, or VDD = +4.75V to +5.25V, V

REF

= +4.096V for MAX1086/MAX1088,

0.1µF capacitor at REF, f

SCLK

= 8MHz (50% duty cycle), AIN- = GND for MAX1088/MAX1089. TA= T

MIN

to T

MAX,

unless otherwise

noted. Typical values at T

= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

VDDto GND.............................................................-0.3V to +6V

CNVST, SCLK, DOUT to GND......................-0.3V to (V

+0.3V)

REF, AIN1(AIN+), AIN2(AIN-) to GND..........-0.3V to (V

+0.3V)

Maximum Current Into Any Pin ...........................................50mA

Continuous Power Dissipation (T

= +70°C)

8-Pin SOT23(derate 9.70mW/°C above T

= +70°C) ....777mW

Operating Temperature Ranges.........................-40°C to +85°C

Storage Temperature Range .............................-60°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

DC ACCURACY (Note 1)

Resolution 10 Bits Relative Accuracy (Note 2) INL ±1.0 LSB Differential Nonlinearity DNL No missing codes over temperature ±1.0 LSB Offset Error ±0.5 ±1.0 LSB Gain Error (Note 3) ±1.0 ±2.0 LSB Gain Temperature Coefficient ±0.8 ppm/°C

Channel-to-Channel Offset Channel-to-Channel Gain Matching ±0.1 LSB

Input Common-Mode Rejection CMR VCM = 0V to VDD; zero scale input ±0.1 mV

DYNAMIC SPECIFICATIONS: (f for MAX1087/MAX1089, 150ksps, f

Signal to Noise Plus Distortion SINAD 61 dB

Total Harmonic Distortion (up to the 5

Spurious-Free Dynamic Range SFDR 70 dB

Full-Power Bandwidth -3dB point 1 MHz

Full-Linear Bandwidth SINAD>56dB 100 kHz

CONVERSION RATE

Conversion Time t

T/H Acquisition Time t

Aperture Delay 30 ns

Aperture Jitter <50 ps

Maximum Serial Clock Frequency f

Duty Cycle 30 70 %

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

harmonic)

(sine-wave) = 10kHz, VIN = 4.096Vp-p for MAX1086/MAX1088 or VIN = 2.5V

= 8MHZ, AIN- = GND for MAX1088/MAX1089)

SCLK

THD -70 dB

CONV

ACQ

SCLK

±0.1 LSB

8 MHz

3.7 µs

1.4 µs

Page 3

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD= +2.7V to +3.6V, V

REF

= +2.5V for MAX1087/MAX1089, or VDD

= +4.75V to +5.25V, V

REF

= +4.096V for MAX1086/MAX1088,

0.1µF capacitor at REF, f

SCLK

= 8MHz (50% duty cycle), AIN- = GND for MAX1088/MAX1089. TA= T

MIN

to T

MAX,

unless otherwise

noted. Typical values at T

= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

ANALOG INPUT

Input Voltage Range (Note 4)

Unipolar 0 V

Bipolar -V

Input Leakage Current C hannel not sel ected or conver si on stop p ed ±0.01 ±1 µA

Input Capacitance 34 pF

EXTERNAL REFERENCE INPUT

Input Voltage Range V

Input Current I

REF

= +2.5V at 150ksps 16 30

REF

= +4.096V at 150ksps 26 45

REF

Acquisition/Between conversions ±0.01 ±1

DIGITAL INPUTS/OUTPUT (SCLK, CNVST, DOUT)

Input Low Voltage V

Input High Voltage V

Input Leakage Current I

Input Capacitance C

Output Low Voltage V

Output High Voltage V

Three-State Leakage Current I

Three-State Output Capacitance C

OUT

= 2mA 0.4 V

SINK

= 4mA 0.8 V

SINK

SOURCE

= 1.5mA

CNVST = GND ±10 µA

CNVST = GND 15 pF

POWER REQUIREMENTS

Positive Supply Voltage V

MAX1086/MAX1088 4.75 5.0 5.25

MAX1087/MAX1089 2.7 3.0 3.6

VDD = +3V

Positive Supply Current I

VDD = +5V

Shutdown 0.2 5

Positive Supply Rejection PSR

VDD = 5V ±5%; full-scale input ±0.1 1.0

= +2.7V to +3.6V; full-scale input ±0.1 ±1.2

=150ksps 245 350

SAMPLE

=100ksps 150

SAMPLE

=10ksps 15

SAMPLE

=1ksps 2

SAMPLE

=150ksps 320 400

SAMPLE

=100ksps 215

SAMPLE

=10ksps 22

SAMPLE

=1ksps 2.5

SAMPLE

REF

1.0

/2 V

REF

+50mV

0.8 V

-1 V

±0.1 µA

15 pF

-0.5

µA

Page 4

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

4 _______________________________________________________________________________________

TIMING CHARACTERISTICS (Figures 1 and 2)

(VDD= +2.7V to +3.6V, V

REF

= +2.5V for MAX1087/MAX1089, or VDD= +4.75V to +5.25V, V

REF

= +4.096V for MAX1086/MAX1088,

0.1µF capacitor at REF, f

SCLK

= 8MHz (50% duty cycle); AIN- = GND for MAX1088/MAX1089. TA= T

MIN

to T

MAX,

unless otherwise

noted. Typical values at T

= +25°C.)

Note 1: Unipolar input. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after offset and gain errors have

been removed.

Note 3: Offset nulled. Note 4: The absolute input range for the analog inputs is from GND to V

Figure 1. Detailed Serial-Interface Timing Sequence

Figure 2. Load Circuits for Enable/Disable Times

PARAMETERS SYMBOL CONDITIONS MIN TYP MAX UNITS

SCLK Pulse Width High t

SCLK Pulse Width Low t

SCLK Fall to DOUT Transition t

SCLK Rise to DOUT Disable t

CNVST Rise to DOUT Enable t

CNVST Fall to MSB Valid t

CNVST Pulse Width t

DOT

DOD

DOE

DOV

CSW

= 30pF 60 ns

LOAD

= 30pF 100 500 ns

LOAD

= 30pF 80 ns

LOAD

= 30pF 3.7 µs

LOAD

38 ns

30 ns

CNVST

SCLK

DOE

HIGH-Z

DOUT

6kΩ

GND

a) HIGH -Z TO VOH, VOL TO VOH, AND VOH TO HIGH -Z

• • •

DOT

GND

• • •

6kΩ

DOUT

a) HIGH -Z TO V

, VOH TO VOL, AND VOL TO HIGH -Z

CSW

DOD

HIGH-Z

Page 5

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(VDD= +3.0V, V

REF

= +2.5V for MAX1087/MAX1089 or VDD= +5.0V, V

REF

= +4.096V for MAX1086/MAX1088, 0.1µF capacitor at

REF, f

SCLK

= 8MHz, (50% Duty Cycle), AIN- = GND for MAX1088/1089, TA= +25°C, unless otherwise noted.)

INTEGRAL NONLINEARITY

vs. OUTPUT CODE

1.0

0.8

0.6

0.4

0.2

INL (LSB)

-0.2

-0.4

-0.6

-0.8

-1.0 0 400200 600 800 1000 1200

OUTPUT CODE

DIFFERENTIAL NONLINEARITY

vs. OUTPUT CODE

1.0

0.8

0.6

0.4

0.2

DNL (LSB)

-0.2

-0.4

-0.6

-0.8

-1.0 0 400 600200 800 1000 1200

OUTPUT CODE

380

330

280

SUPPLY CURRENT ( µA)

230

180

2.7 3.73.2 4.2 4.7 5.2

MAX1087/MAX1089

MAX1086-9 toc01

MAX1086/MAX1088

MAX1086-9 toc04

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

VDD (V)

INTEGRAL NONLINEARITY

vs. OUTPUT CODE

1.0

0.8

0.6

0.4

0.2

INL (LSB)

-0.2

-0.4

-0.6

-0.8

-1.0 0 400200 600 800 1000 1200

SUPPLY CURRENT

vs. SAMPLING RATE

1000

MAX1087/MAX1089

100

SUPPLY CURRENT (µA)

0.1

0.001 10 1000

MAX1086-9 toc07

1.0

SAMPLING RATE (ksps)

MAX1086/MAX1088

OUTPUT CODE

SHUTDOWN CURRENT (nA)

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

2.7 3.73.2 4.2 4.7 5.2

1.0

0.8

0.6

MAX1086-9 toc02

0.4

0.2

DNL (LSB)

-0.2

-0.4

-0.6

-0.8

-1.0 0 400 600200 800 1000 1200

1000

MAX1086/MAX1088

MAX1086-9 toc05

100

SUPPLY CURRENT (µA)

0.1

0.001 10 10001.0

SHUTDOWN CURRENT vs. SUPPLY VOLTAGE

VDD (V)

DIFFERENTIAL NONLINEARITY

vs. OUTPUT CODE

MAX1087/MAX1089

MAX1086-9 toc03

OUTPUT CODE

SUPPLY CURRENT

vs. SAMPLING RATE

MAX1086-9 toc06

SAMPLING RATE (ksps)

MAX1086-9 toc08

Page 6

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= 3.0V, V

REF

= 2.5V for MAX1087/MAX1089 or VDD= 5.0V, V

REF

= +4.096V for MAX1086MAX1088, 0.1µF capacitor at REF,

SCLK

= 8MHz, (50% Duty Cycle), AIN- = GND for MAX1088/89, TA= +25°C, unless otherwise noted.)

100

250

200

150

300

-40 0 20-20 40 60 80

SHUTDOWN CURRENT

vs. TEMPERATURE

MAX1086-9 toc10

TEMPERATURE (°C)

SHUTDOWN CURRENT (nA)

-1.00

-0.40

0.60

-0.80

0.00

-0.20

0.80

0.60

0.40

0.20

1.00

-40 -20 0 20 40 60 80

OFFSET ERROR

vs. TEMPERATURE

MAX1086-9 toc11

TEMPERATURE (°C)

OFFSET ERROR (LSB)

-1.0

-0.6

-0.8

-0.2

-0.4

0.2

0.4

0.6

0.8

1.0

2.7 3.7 4.23.2 4.7 5.2

OFFSET ERROR

vs. SUPPLY VOLTAGE

MAX1086-9 toc12

VDD (V)

OFFSET ERROR (LSB)

-40 0 20-20 40 60 80

GAIN ERROR

vs. TEMPERATURE

MAX1086-9 toc13

TEMPERATURE (°C)

GAIN ERROR (LSB)

-1.0

-0.6

-0.8

-0.2

-0.4

0.2

0.4

0.6

0.8

1.0

2.7 3.73.2 4.2 4.7 5.2

GAIN ERROR

vs. SUPPLY VOLTAGE

MAX1086-9 toc14

VDD (V)

GAIN ERROR (LSB)

-1.0

-0.6

-0.8

-0.2

-0.4

0.2

0.4

0.6

0.8

1.0

-140.00

-120.00

-100.00

-80.00

-60.00

-40.00

-20.00

0.00

20.00

03015 45 60

FFT PLOT (SINAD)

MAX1086-9 toc15

FREQUENCY (kHz)

AMPLITUDE (dB)

180

280

230

330

380

-40 0-20 20 40 60 80

SUPPLY CURRENT

vs. TEMPERATURE

MAX1086-9 toc09

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

Page 7

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

_______________________________________________________________________________________ 7

Detailed Description

The MAX1086–MAX1089 analog-to-digital converters (ADCs) use a successive-approximation conversion (SAR) technique and an on-chip track-and-hold (T/H) structure to convert an analog signal into a 10-bit digital result.

The serial interface provides easy interfacing to microprocessors (µPs). Figure 3 shows the simplified internal structure for the MAX1086/MAX1087 (2–channels, single-ended) and the MAX1088/MAX1089 (1–channel, true-differential).

True-Differential Analog Input Track/Hold

The equivalent circuit of Figure 4 shows the MAX1086–MAX1089’s input architecture which is composed of a T/H, input multiplexer, comparator, and switched-capacitor DAC. The T/H enters its tracking mode on the rising edge of CNVST. The positive input capacitor is connected to AIN1 or AIN2 (MAX1086/ MAX1087) or AIN+ (MAX1088/MAX1089). The negative input capacitor is connected to GND (MAX1086/ MAX1087) or AIN- (MAX1088/MAX1089). The T/H enters its hold mode on the falling edge of CNVST and the difference between the sampled positive and negative input voltages is converted. The time required for the T/H to acquire an input signal is determined by how quickly its input capacitance is charged. If the input signal’s source impedance is high, the acquisition time lengthens, and CNVST must be held high for a longer period of time. The acquisition time, t

ACQ

, is the maximum time needed for the signal to be acquired, plus the power-up time. It is calculated by the following equation:

ACQ

= 7 x (RS+ RIN) x 24pF + t

PWR

Pin Description

Figure 3. Simplified Functional Diagram

NAME

MAX1086 MAX1087

1VDDV

2 AIN1 AIN+ Analog Input Channel 1 (MAX1086/MAX1087) or Positive Analog Input (MAX1088/MAX1089)

3 AIN2 AIN- Analog Input Channel 2 (MAX1086/MAX1087) or Negative Analog Input (MAX1088/MAX1089)

4 GND GND Ground

5 REF REF

6 CNVST CNVST

7 DOUT DOUT

8 SCLK SCLK Serial Clock Input. Clocks out data at DOUT MSB first.

MAX1088 MAX1089

Positive Supply Voltage. +2.7V to +3.6V (MAX1087/MAX1089); +4.75V to +5.25V (MAX1086/MAX1088). Bypass with a 0.1µF capacitor to GND.

External Reference Voltage Input. Sets the analog voltage range. Bypass with a 0.1µF capacitor to GND.

Conversion Start. A rising edge powers-up the IC and places it in track mode. At the falling edge of CNVST, the device enters hold mode and begins conversion. CNVST also selects the input channel (MAX1086/MAX1087) or input polarity (MAX1088/MAX1089).

Serial Data Output. DOUT transitions the falling edge of SCLK. DOUT goes low at the start of a conversion and presents the MSB at the completion of a conversion. DOUT goes highimpedance once data has been fully clocked out.

FUNCTION

MAX1086–MAX1089

OSCILLATOR

CNVST

SCLK

INPUT SHIFT

CONTROL

AIN1

(AIN+)

AIN2

(AIN-)

REF

T/H

10-BIT

SAR ADC

DOUT

( ) ARE FOR MAX1088/MAX1089

Page 8

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

8 _______________________________________________________________________________________

where RIN= 1.5kΩ, RSis the source impedance of the input signal, and t

PWR

= 1µs is the power-up time of the

device.

Note: t

ACQ

is never less than 1.4µs and any source

impedance below 300Ω does not significantly affect the ADC‘s AC performance. A high impedance source can be accommodated either by lengthening t

ACQ

or by placing a 1µF capacitor between the positive and negative analog inputs.

Selecting AIN1 or AIN2

(MAX1086/MAX1087)

Select between the MAX1086/MAX1087’s two positive input channels using the CNVST pin. If AIN1 is desired (Figure 5a), drive CNVST high to power-up the ADC and place the T/H in track mode with AIN1 connected to the positive input capacitor. Hold CNVST high for t

ACQ

to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. Be sure to clock out all 12 bits of data (the 10-bit result plus two sub-bits) before driving CNVST high for the next conversion. If all 12 bits of data are not clocked out before CNVST is driven high, AIN2 will be selected for the next conversion.

If AIN2 is desired (Figure 5b), drive CNVST high for at least 30ns. Next, drive it low for at least 30ns, and then high again. This will power-up the ADC and place the T/H in track mode with AIN2 connected to the positive input capacitor. Now hold CNVST high for t

ACQ

to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at

DOUT after 3.7µs. Data can then be clocked out using SCLK. If all 12 bits of data are not clocked out before CNVST is driven high, AIN2 will be selected for the next conversion.

Selecting Unipolar or Bipolar Conversions

(MAX1088/MAX1089)

Initiate true-differential conversions with the MAX1088/MAX1089’s unipolar and bipolar modes, using the CNVST pin. AIN+ and AIN- are sampled at the falling edge of CNVST. In unipolar mode, AIN+ can exceed AIN- by up to V

REF

. The output format is straight binary. In bipolar mode, either input can exceed the other by up to V

REF

/2. The output format is

two’s complement.

Note: In both modes, AIN+ and AIN- must not exceed VDDby more than 50mV or be lower than GND by more than 50mV.

If unipolar mode is desired (Figure 5a), drive CNVST high to power-up the ADC and place the T/H in track mode with AIN+ and AIN- connected to the input capacitors. Hold CNVST high for t

ACQ

to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. Be sure to clock out all 12 bits (the 10-bit result plus two sub-bits) of data before driving CNVST high for the next conversion. If all 12 bits of data are not clocked out before CNVST is driven high, bipolar mode will be selected for the next conversion.

If bipolar mode is desired (Figure 5b), drive CNVST high for at least 30ns. Next, drive it low for at least 30ns and then high again. This will place the T/H in track mode with AIN+ and AIN- connected to the input capacitors. Now hold CNVST high for t

ACQ

to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. If all 12 bits of data are not clocked out before CNVST is driven high, bipolar mode will be selected for the next conversion.

Input Bandwidth

The ADCs input tracking circuitry has a 1MHz smallsignal bandwidth, so it is possible to digitize highspeed transient events and measure periodic signals with bandwidths exceeding the ADC’s sampling rate by using undersampling techniques. To avoid high frequency signals being aliased into the frequency band of interest, anti-alias filtering is recommended.

Figure 4. Equivalent Input Circuit

AIN2

AIN1(AIN+)

HOLD

GND(AIN-)

*( ) APPLIES TO MAX1088/1089

REF

GND

CIN+

CIN-

HOLD

DAC

COMPARATOR

RIN-

RIN+

HOLD

TRACK

Page 9

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

_______________________________________________________________________________________ 9

Analog Input Protection

Internal protection diodes which clamp the analog input to VDDand GND allow the analog input pins to swing from GND - 0.3V to VDD+ 0.3V without damage. Both inputs must not exceed VDDby more than 50mV or be lower than GND by more than 50mV for accurate conversions. If an off-channel analog input voltage exceeds

the supplies, limit the input current to 2mA.

Internal Clock

The MAX1086–MAX1089 operate from an internal oscillator, which is accurate within 10% of the 4MHz specified clock rate. This results in a worse case conversion time of 3.7µs. The internal clock releases the system microprocessor from running the SAR conversion clock and allows the conversion results to be read back at the processor’s convenience, at any clock rate from 0 to 8MHz.

Figure 5b. Single Conversion AIN2 vs. GND (MAX1086/MAX1087), bipolar mode AIN+ vs. AIN- (MAX1088/MAX1089)

Figure 5a. Single Conversion AIN1 vs. GND (MAX1086/MAX1087), unipolar mode AIN+ vs. AIN- (MAX1088/MAX1089)

CONV

CNVST

ACQ

SCLK

DOUT

HIGH-Z

ACQ

CNVST

SCLK

DOUT

HIGH-Z

MSB

SAMPLING INSTANT

CONV

MSB

B8 B7 B6 B5

41812

B3 B2 B1

41812

B3 B2 B1

LSB

S1 S0

HIGH-Z

SAMPLING INSTANT

Page 10

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

10 ______________________________________________________________________________________

Output Data Format

Figures 5a and 5b illustrate the conversion timing for the MAX1086–MAX1089. The 10-bit conversion result is output in MSB first format, followed by two sub-bits (S1 and S0). Data on DOUT transitions on the falling edge of SCLK. All 12-bits must be clocked out before CNVST transitions again. For the MAX1088/MAX1089, data is straight binary for unipolar mode and two’s complement for bipolar mode. For the MAX1086/MAX1087, data is always straight binary.

Applications Information

Automatic Shutdown Mode

With CNVST low, the MAX1086–MAX1089 defaults to an AutoShutdown state (<0.2µA) after power-up and between conversions. After detecting a rising edge on CNVST, the part powers up, sets DOUT low and enters track mode. After detecting a falling-edge on CNVST, the device enters hold mode and begins the conversion. A maximum of 3.7µs later, the device completes conversion, enters shutdown and MSB is available at DOUT.

External Reference

An external reference is required for the MAX1086– MAX1089. Use a 0.1µF bypass capacitor for best performance. The reference input structure allows a voltage range of +1V to VDD+ 50mV.

Transfer Function

Figure 6 shows the unipolar transfer function for the MAX1086–MAX1089. Figure 7 shows the bipolar transfer function for the MAX1088/MAX1089. Code transitions occur halfway between successive-integer LSB values.

Connection to Standard Interfaces

The MAX1086–MAX1089 feature a serial interface that is fully compatible with SPI, QSPI, and MICROWIRE. If a serial interface is available, establish the CPU’s serial interface as a master, so that the CPU generates the serial clock for the ADCs. Select a clock frequency up to 8MHz.

How to Perform a Conversion

1) Use a general purpose I/O line on the CPU to hold

CNVST low between conversions.

2) Drive CNVST high to acquire AIN1(MAX1086/

MAX1087) or unipolar mode (MAX1088/MAX1089). To acquire AIN2(MAX1086/MAX1087) or bipolar mode (MAX1088/MAX1089), drive CNVST low and high again.

3) Hold CNVST high for 1.4µs.

4) Drive CNVST low and wait approximately 3.7µs for

conversion to complete. After 3.7µs, the MSB is available at DOUT.

5) Activate SCLK for a minimum of 12 rising clock

edges. DOUT transitions on SCLK’s falling edge

Figure 6. Unipolar Transfer Function

Figure 7. Bipolar Transfer Function

OUTPUT CODE

11 . . . 111

11 . . . 110

11 . . . 101

00 . . . 011

00 . . . 010

00 . . . 001

00 . . . 000

123

FULL-SCALE TRANSITION

INPUT VOLTAGE (LSB)

MAX1086– MAX1089

FS = V

ZS = GND

1LSB =

FS - 3/2LSB

REF

1024

REF

011 . . . 111

011 . . . 110

000 . . . 010

000 . . . 001

000 . . . 000

111 . . . 111

111 . . . 110

111 . . . 101

100 . . . 001

100 . . . 000

COM

OUTPUT CODE

ZS = 0

-FS =

1LSB =

- FS

≤

/ 2 *VIN = (AIN+) - (AIN-)

REF

-V

REF

2 V

REF

1024

INPUT VOLTAGE (LSB)

MAX1088/MAX1089

+FS - 1LSB

Page 11

and is available in MSB-first format. Observe the SCLK to DOUT valid timing characteristic. Clock data into the µP on SCLK’s rising-edge.

SPI and MICROWIRE Interface

When using SPI interface (Figure 8a) or MICROWIRE (Figure 8a and 8b), set CPOL = CPHA = 0. Two 8-bit readings are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clock’s falling edge and is clocked into the µP on SCLK’s rising edge. The first 8-bit data stream contains the first 8-bits of DOUT starting with the MSB. The second 8-bit data stream contains the remaining two result bits (B1, B0) and two trailing sub-bits (S1, S0). DOUT then goes high impedance.

QSPI Interface

Using the high-speed QSPI interface (Figure 9a) with CPOL = 0 and CPHA = 0, the MAX1086–MAX1089 support a maximum f

SCLK

of 8MHz. One 8- to16-bit reading is necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clock’s falling edge and is clocked into the µP on

SCLK’s rising edge. The first 10 bits are the data and the next two bits are sub-bits (S1, S0). DOUT then goes high impedance (Figure 9b).

PIC16 and SSP Module and

PIC17 Interface

The MAX1086–MAX1089 are compatible with a PIC16/PIC17 microcontroller (µC), using the synchronous serial port (SSP) module

To establish SPI communication, connect the controller as shown in Figure 10a and configure the PIC16/PIC17 as system master. This is done by initializing its synchronous serial port control register (SSPCON) and synchronous serial port status register (SSPSTAT) to the bit patterns shown in Tables 1 and 2.

In SPI mode, the PIC16/PIC17 µCs allow eight bits of data to be synchronously transmitted and received simultaneously. Two consecutive 8-bit readings (Figure 10b) are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clock’s falling edge and is clocked into the µC on SCLK’s rising edge. The first 8-bit data stream contains

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

______________________________________________________________________________________ 11

Figure 8a. SPI Connections Figure 8b. MICROWIRE Connections

Table 1. Detailed SSPCON Register Content

SPI

SCK

MISO

I/O

CNVST

SCLK

DOUT

MAX1086– MAX1089

I/O

MICROWIRE

CNVST

SCLK

DOUT

MAX1086– MAX1089

CONTROL BIT

WCOL Bit 7 X Write Collision Detection Bit

SSPOV Bit 6 X Receive Overflow Detect Bit

SSPEN Bit 5 1

CKP Bit 4 0 Clock Polarity Select Bit. CKP = 0 for SPI master mode selection.

SSPM3 Bit 3 0

SSPM2 Bit 2 0

SSPM1 Bit 1 0

SSPM0 Bit 0 1

X = Don’t care

MAX1086–MAX1089

SETTINGS

SYNCHRONOUS SERIAL PORT CONTROL REGISTER (SSPCON)

Synchronous Serial Port Enable Bit. 0: Disables serial port and configures these pins as I/O port pins. 1: Enables serial port and configures SCK, SDO and SCI pins as serial port pins.

Synchronous Serial Port Mode Select Bit. Sets SPI master mode and selects

= f

OSC

/ 16.

CLK

Page 12

MAX1086–MAX1089

the first eight data bits starting with the MSB. The second 8-bit data stream contains the remaining bits, D1 through D0, and the two sub-bits S1 and S0.

Layout, Grounding, and Bypassing

For best performance, use printed circuit (PC) boards. Wire-wrap configurations are not recommended since the layout should ensure proper separation of analog

and digital traces. Do not run analog and digital lines parallel to each other, and do not lay out digital signal paths underneath the ADC package. Use separate analog and digital PC board ground sections with only one starpoint (Figure 11), connecting the two ground systems (analog and digital). For lowest-noise operation, ensure the ground return to the star ground’s power supply is low impedance and as short as possible. Route digital signals far away from sensitive analog and reference inputs.

High-frequency noise in the power supply (VDD) may degrade the performance of the ADC’s fast comparator. Bypass V

to the star ground with a 0.1µF capacitor, located as close as possible to the MAX1086–MAX1089s power supply pin. Minimize capacitor lead length for best supply-noise rejection. Add an attenuation resistor (5Ω) if the power supply is extremely noisy.

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

12 ______________________________________________________________________________________

Figure 9a. QSPI Connections

Table 2. Detailed SSPSTAT Register Content

Figure 8c. SPI/MICROWIRE Interface Timing Sequence (CPOL = CPHA = 0)

CNVST

1ST BYTE READ

2ND BYTE READ

SCLK

DOUT

B8 B7 B6 B5

MSB

SAMPLING INSTANT

418

B3 B2 B1

CNVST

SCLK

DOUT

MAX1086– MAX1089

QSPI

SCK

MISO

LSB

S1 S0

HIGH-Z

CONTROL BIT

SMP Bit 7 0

CKE Bit 6 1 SPI Clock Edge Select Bit. Data will be transmitted on the rising edge of the serial clock.

D/A

P Bit 4 X Stop Bit

S Bit 3 X

R/W

UA Bit 1 X

BF Bit 0 X

X = Don’t care

MAX1086–MAX1089

SETTINGS

SPI Data Input Sample Phase. Input data is sampled at the middle of the data output time.

Bit 5 X Data Address Bit

Start Bit

Bit 2 X

Read/Write Bit Information

Update Address

Buffer Full Status Bit

SYNCHRONOUS SERIAL STATUS REGISTER (SSPSTAT)

Page 13

Definitions

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values on an actual transfer function from a straight line. This straight line can be either a best-straight-line fit or a line drawn between the endpoints of the transfer function, once offset and gain errors have been nullified. The static linearity parameters for the MAX1086–MAX1089 are measured using the endpoint method.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between an actual step-width and the ideal value of 1LSB. A DNL error specification of less than 1LSB guarantees no missing codes and a monotonic transfer function.

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

______________________________________________________________________________________ 13

Figure 9b. QSPI Interface Timing Sequence (CPOL = CPHA = 0)

Figure 10a. SPI Interface Connection for a PIC16/PIC17 Controller

Figure 10b. SPI Interface Timing with PIC16/PIC17 in Master Mode (CKE = 1, CKP = 0, SMP = 0, SSPM3 - SSPM0 = 0001)

CNVST

SCLK

DOUT

B8 B7 B6 B5

MSB

SAMPLING INSTANT

418

B3 B2 B1

SCLK

DOUT

CNVST

SCK

SDI

I/O

PIC16/PIC17

MAX1086– MAX1089

GND GND

LSB

S1 S0

HIGH-Z

CNVST

SCLK

DOUT

B8 B7 B6 B5

MSB

SAMPLING INSTANT

1ST BYTE READ

418

B3 B2 B1

LSB

S1 S0

2ND BYTE READ

HIGH-Z

Page 14

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23

14 ______________________________________________________________________________________

Aperture Definitions

Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples. Aperture delay (tAD) is the time between the rising edge of the sampling clock and the instant when an actual sample is taken.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (SNR) is the ratio of full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-todigital noise is caused by quantization error only and results directly from the ADC’s resolution (N-bits):

SNR = (6.02

✕ N + 1.76)dB

In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, etc. SNR is computed by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five harmonics, and the DC offset.

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s RMS amplitude to RMS equivalent of all other ADC output signals.

SINAD (dB) = 20 ✕ log (Signal

RMS

/ Noise

RMS

)

Effective Number of Bits

Effective number of bits (ENOB) indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC’s error consists of quantization noise only. With an input range equal to the fullscale range of the ADC, calculate the effective number of bits as follows:

ENOB = (SINAD - 1.76) / 6.02

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the RMS sum of the first five harmonics of the input signal to the fundamental itself. This is expressed as:

where V1is the fundamental amplitude, and V2through V5are the amplitudes of the 2nd- through 5th-order harmonics.

Spurious-Free Dynamic Range

Spurious-free dynamic range (SFDR) is the ratio of RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next largest distortion component.

Chip Information

TRANSISTOR COUNT: 6922

PROCESS: BiCMOS

Figure 11. Power-Supply and Grounding Connections

SUPPLIES

+3V OR +5V

R* = 5Ω

0.1µF

*OPTIONAL

GND

MAX1086–

MAX1089

LOGIC

= +5V/+3V

CIRCUITRY

GND

DGND+5V/+3V

DIGITAL

THD VVVV V=× +++





log /











Page 15

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and

1-Channel True-Differential ADCs in SOT23

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15

Package Information

SOT23, 8L.EPS