results may be read. Input overvoltage protection is

active in all power-down modes. The device returns to

normal operation on the first WR falling edge during

write operation.

Choosing Power-Down Modes

The bandgap reference and reference buffer remain

active in STBYPD mode, maintaining the voltage on the

4.7µF capacitor at the REF pin. This is a “DC” state that

does not degrade after power-down of any duration.

Therefore, you can use any sampling rate with this

mode, without regard to start-up delays.

However, in FULLPD mode, only the bandgap refer-

ence is active. Connect a 33µF capacitor between REF

and AGND to maintain the reference voltage between

conversions and to reduce transients when the buffer is

enabled and disabled. Throughput rates down to 1ksps

can be achieved without allotting extra acquisition time

for reference recovery prior to conversion. This allows

conversion to begin immediately after power-down

ends. If the discharge of the REF capacitor during

FULLPD exceeds the desired limits for accuracy (less

than a fraction of an LSB), run a STBYPD power-down

cycle prior to starting conversions. Take into account

that the reference buffer recharges the bypass capaci-

tor at an 80mV/ms slew rate, and add 50µs for settling

time. Throughput rates of 10ksps offer typical supply

currents of 470µA, using the recommended 33µF

capacitor value.

Auto-Shutdown

Selecting STBYPD on every conversion automatically

shuts the MAX196/MAX198 down after each conversion

without requiring any start-up time on the next conversion.

Transfer Function

Output data coding for the MAX196/MAX198 is binary

in unipolar mode with 1LSB = (FS / 4096) and twos-

complement binary in bipolar mode with 1LSB = [(2 x

successive-integer LSB values. Figures 10 and 11

show the input/output (I/O) transfer functions for unipo-

lar and bipolar operations, respectively. For full-scale

(FS) values, refer to Table 1.

Multirange, Single +5V, 12-Bit DAS

with 12-Bit Bus Interface

14

______________________________________________________________________________________

OUTPUT CODE

INPUT VOLTAGE (LSB)

0

FS

1 LSB =

FULL-SCALE

TRANSITION

12

3

11... 111

11... 110

11... 101

00... 011

00... 010

00... 001

00... 000

FS

4096

Figure 10. Unipolar Transfer Function

OUTPUT CODE

INPUT VOLTAGE (LSB)

0V

+FS - 1 LSB

1 LSB =

-FS

011... 111

011... 110

000... 001

000... 000

111... 111

100... 010

100... 001

100... 000

2

FS

4096

Figure 11. Bipolar Transfer Function