MAX195B View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX195B

16-Bit, 85ksps ADC with 10µA Shutdown

Maxim Integrated 

16-Bit, 85ksps ADC with 10µA Shutdown

MSB

32,768C

16,384C

LSB

DUMMY

4C

2C

C

C

AIN

REF

AGND

Figure 1. Capacitor DAC Functional Diagram

tCAL

CLK

RESET

tRCH

tRCS

EOC

CALIBRATION

BEGINS

MAX195

OPERATION HALTS

Figure 2. Initiating Calibration

CALIBRATION

ENDS

Calibration

In an ideal DAC, each of the capacitors associated with

the data bits would be exactly twice the value of the

next smaller capacitor. In practice, this results in a

range of values too wide to be realized in an economi-

cally feasible size. The capacitor array actually consists

of two arrays, which are capacitively coupled to reduce

the LSB array’s effective value. The capacitors in the

MSB array are production trimmed to reduce errors.

Small variations in the LSB capacitors contribute

insignificant errors to the 16-bit result.

Unfortunately, trimming alone does not yield 16-bit per-

formance or compensate for changes in performance

due to changes in temperature, supply voltage, and

other parameters. For this reason, the MAX195 includes

a calibration DAC for each capacitor in the MSB array.

These DACs are capacitively coupled to the main DAC

output and offset the main DAC’s output according to

the value on their digital inputs. During calibration, the

correct digital code to compensate for the error in each

MSB capacitor is determined and stored. Thereafter,

the stored code is input to the appropriate calibration

DAC whenever the corresponding bit in the main DAC

is high, compensating for errors in the associated

capacitor.

The MAX195 calibrates automatically on power-up. To

reduce the effects of noise, each calibration experiment

is performed many times and the results are averaged.

Calibration requires about 14,000 clock cycles, or

8.2ms at the highest clock (CLK) speed (1.7MHz). In

addition to the power-up calibration, bringing RESET

low halts MAX195 operation, and bringing it high again

initiates a calibration (Figure 2).

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