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MAX187/MAX189

+5V, Low-Power, 12-Bit Serial ADCs

Functional Diagram

19-0196; Rev 1; 3/12

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part,

refer to www.maximintegrated.com/MAX187.related.

EVALUATION KIT AVAILABLE

General Description

The MAX187/MAX189 serial 12-bit analog-to-digital con-

verters (ADCs) operate from a single +5V supply and

accept a 0 to 5V analog input. Both parts feature an 8.5Fs

successive-approximation ADC, a fast track/hold (1.5Fs),

an on-chip clock, and a high-speed 3-wire serial interface.

The MAX187/MAX189 digitize signals at a 75ksps

throughput rate. An external clock accesses data from

the interface, which communicates without external

hardware to most digital signal processors and micro-

controllers. The interface is compatible with SPI, QSPIK,

and MICROWIRE

The MAX187 has an on-chip buffered reference, and

the MAX189 requires an external reference. Both the

MAX187 and MAX189 save space with 8-pin PDIP and

16-pin SO packages. Power consumption is 7.5mW and

reduces to only 10FW in shutdown.

Excellent AC characteristics and very low power con-

sumption combined with ease of use and small package

size make these converters ideal for remote DSP and

sensor applications, or for circuits where power con-

sumption and space are crucial.

Features

S 12-Bit Resolution

S ±½ LSB Integral Nonlinearity (MAX187A/MAX189A)

S Internal Track/Hold, 75kHz Sampling Rate

S Single +5V Operation

S Low Power: 2µA Shutdown Current

1.5mA Operating Current

S Internal 4.096V Buffered Reference (MAX187)

S 3-Wire Serial Interface, Compatible with SPI, QSPI,

and MICROWIRE

S Small-Footprint 8-Pin PDIP and 16-Pin SO

Applications

Portable Data Logging

Remote Digital Signal Processing

Isolated Data Acquisition

High-Accuracy Process Control

QSPI is a trademark of Motorola.

MICROWIRE is a registered trademark of National Semiconductor Corp.

GND 5

REF

AIN

T/H

BANDGAP

REFERENCE

+2.5V

(MAX187 ONLY)

10kI

= 1.638

(4.096V)

REF-

REF+

DAC

OUTPUT

SHIFT

DOUT6

SCLK

CS7

CONTROL

AND

TIMING

12-BIT

SAR

COMPARATOR

BUFFER ENABLE/DISABLE

NOTE: PIN NUMBERS SHOWN ARE FOR 8-PIN DIPs ONLY

SHDN

MAX187

MAX189

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

Summary of content (18 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs General Description Features The MAX187/MAX189 serial 12-bit analog-to-digital converters (ADCs) operate from a single +5V supply and accept a 0 to 5V analog input. Both parts feature an 8.5Fs successive-approximation ADC, a fast track/hold (1.5Fs), an on-chip clock, and a high-speed 3-wire serial interface. S 12-Bit Resolution The MAX187/MAX189 digitize signals at a 75ksps throughput rate.
PAGE 2
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Absolute Maximum Ratings VDD to GND .............................................................-0.3V to +6V AIN to GND................................................-0.3V to (VDD + 0.3V) REF to GND ...............................................-0.3V to (VDD + 0.3V) Digital Inputs to GND.................................-0.3V to (VDD + 0.3V) Digital Outputs to GND..............................-0.3V to (VDD + 0.3V) SHDN to GND................................
PAGE 3
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V ±5%; VGND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187—internal reference: VREF = 4.096V, 4.7µF capacitor at REF pin, or MAX189—external reference: VREF = 4.096V applied to REF pin, 4.7µF capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.
PAGE 4
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs ELECTRICAL CHARACTERISTICS (continued) (VDD = +5V ±5%; VGND = 0V; unipolar input mode; 75ksps, fCLK = 4.0MHz, external clock (50% duty cycle); MAX187—internal reference: VREF = 4.096V, 4.7µF capacitor at REF pin, or MAX189—external reference: VREF = 4.096V applied to REF pin, 4.7µF capacitor at REF pin; TA = TMIN to TMAX; unless otherwise noted.
PAGE 5
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Typical Operating Characteristics POWER-SUPPLY REJECTION vs. TEMPERATURE VREF vs. TEMPERATURE 0.12 0.10 0.08 0.06 0.04 0.02 4.089 4.088 4.087 4.086 4.085 4.084 4.083 4.082 4.081 0 4.080 -20 20 60 100 140 -60 -20 20 60 100 TEMPERATURE (°C) TEMPERATURE (°C) SUPPLY vs. TEMPERATURE SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 1.8 MAX187 1.4 MAX189 1.0 0.6 140 MAX187 toc04 2.
PAGE 6
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Pin Configurations TOP VIEW 1 + VDD SCLK 2 MAX187 AIN MAX189 3 SHDN 4 REF 8 CS 7 DOUT 6 GND 5 PDIP VDD 1 + 16 SCLK N.C. 2 15 CS AIN 3 MAX187 MAX189 N.C. 4 14 N.C. 13 N.C. N.C. 5 12 DOUT SHDN 6 11 DGND N.C. 7 10 AGND REF 8 9 N.C. Wide SO Pin Description PIN PDIP WIDE SO NAME FUNCTION 1 1 VDD Supply Voltage. +5V, Q5% 2 3 AIN Sampling Analog Input. 0V to VREF range 3 6 4 8 SHDN Three-Level Shutdown Input.
PAGE 7
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Detailed Description# Converter Operation The MAX187/MAX189 use input track/hold (T/H) and successive approximation register (SAR) circuitry to convert an analog input signal to a digital 12-bit output. No external hold capacitor is needed for the T/H. Figures 3a and 3b show the MAX187/MAX189 in their simplest configuration. The MAX187/MAX189 convert input signals in the 0V to VREF range in 10µs, including T/H acquisition time.
PAGE 8
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs 4.7µF 4.7µF 0.1µF 0.1µF 1 +5V ANALOG INPUT 0 TO +5V 2 SHUTDOWN INPUT 3 ON AIN MAX187 SHDN 4 OFF SCLK VDD CS DOUT GND REF 8 +5V 7 SERIAL INTERFACE OFF REFERENCE INPUT 5 4.7µF Figure 3a. MAX187 Operational Diagram 12-BIT CAPACITIVE DAC TRACK INPUT CHOLD 16pF - CPACKAGE CSWITCH COMPARATOR ZERO + RIN 5kI HOLD TRACK GND 3 SCLK VDD AIN MAX189 SHDN CS DOUT 8 7 SERIAL INTERFACE 6 ON 4 REF GND 5 0.1µF Figure 3b.
PAGE 9
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Input Protection Internal protection diodes that clamp the analog input allow the input to swing from GND - 0.3V to VDD + 0.3V without damage. However, for accurate conversions near full scale, the input must not exceed VDD by more than 50mV, or be lower than GND by 50mV. If the analog input exceeds the supplies by more than 50mV beyond the supplies, limit the input current to 2mA, since larger currents degrade conversion accuracy.
PAGE 10
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Serial Interface Initialization After Power-Up and Starting a Conversion When power is first applied, it takes the fully discharged 4.7FF reference bypass capacitor up to 20ms to provide adequate charge for specified accuracy. With SHDN not pulled low, the MAX187/MAX189 are now ready to convert. To start a conversion, pull CS low. At CS’s falling edge, the T/H enters its hold mode and a conversion is initiated. After an internally timed 8.
PAGE 11
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs CS 1 SCLK 4 B11 B10 B9 DOUT 8 B8 B7 B6 B5 12 B4 B3 B2 B1 B0 EOC INTERFACE IDLE A/D STATE TRACK CONVERSION IN PROGRESS EOC CONVERSION 0 8.5µs (tCONV) TRAILING ZEROS CLOCK OUTPUT DATA IDLE TRACK 0µs MINIMUM CYCLE TIME CONV. 1 0µs 12 x 0.250µs = 3.25µs 0.5µs (tCS) TOTAL = 12.25µs Figure 8.
PAGE 12
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Minimum cycle time is accomplished by using DOUT’s rising edge as the EOC signal. Clock out the data with 13 clock cycles at full speed. Raise CS after the conversion’s LSB has been read. After the specified minimum time, tACQ, CS can be pulled low again to initiate the next conversion. Output Coding and Transfer Function The data output from the MAX187/MAX189 is binary, and Figure 10 depicts the nominal transfer function.
PAGE 13
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs The effective resolution (effective number of bits) the ADC provides can be determined by transposing the above equation and substituting in the measured SINAD: N = (SINAD - 1.76)/6.02. Figure 12 shows the effective number of bits as a function of the input frequency for the MAX187/MAX189.
PAGE 14
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs QSPI I/O Set CPOL = CPHA = 0. Unlike SPI, which requires two 1-byte reads to acquire the 12 bits of data from the ADC, QSPI allows the minimum number of clock cycles necessary to clock in the data. The MAX187/MAX189 require 13 clock cycles from the FP to clock out the 12 bits of data with no trailing 0s (Figure 15). The maximum clock frequency to ensure compatibility with QSPI is 2.77MHz.
PAGE 15
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs SCLK CS tCONV HI-Z HI-Z DOUT MSB D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB EOC Figure 15. QSPI Serial Interface Timing (CPOL = CPHA = 0) +5V ON THIS SIDE OF BARRIER MUST BE ISOLATED POWER +5V 3kI 6N136 +5V 1 8 2 7 CS/START SCLK/INPUT CLOCK 200I 3 6 4 74HC04 5 10µF 6N136 MAX187 0.1µF 1 2 4 ANALOG INPUT 5 4.
PAGE 16
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Layout, Grounding, Bypassing For best performance, use printed circuit boards. Wirewrap boards are not recommended. Board layout should ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or digital lines underneath the ADC package. Figure 17 shows the recommended system ground connections.
PAGE 17
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Ordering Information PINPACKAGE ERROR (LSB) PART TEMP RANGE MAX187ACPA+ 0NC to +70NC 8 PDIP ±1/2 MAX187BCPA+ 0NC to +70NC 8 PDIP ±1 MAX187CCPA+ 0NC to +70NC 8 PDIP ±2 MAX187ACWE+ 0NC to +70NC 16 Wide SO ±1/2 MAX187BCWE+ 0NC to +70NC 16 Wide SO ±1 MAX187CCWE+ 0NC to +70NC 16 Wide SO MAX187AEPA+ -40NC to +85NC 8 PDIP ±1/2 MAX187BEPA+ -40NC to +85NC 8 PDIP ±1 MAX187CEPA+ -40NC to +85NC 8 PDIP ±2 MAX187AEWE+ -40NC to +85NC
PAGE 18
MAX187/MAX189 +5V, Low-Power, 12-Bit Serial ADCs Revision History REVISION NUMBER REVISION DATE 0 10/93 Initial release 1 3/12 Updated the Electrical Characteristics and Ordering Information. DESCRIPTION PAGES CHANGED — 1, 3, 18 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.