Power-Down Mode

To save power, you can put the converter into low-

current shutdown mode between conversions. Two

programmable power-down modes are available, in

addition to a hardware shutdown. Select STBYPD or

FULLPD by programming PD0 and PD1 in the input

control byte. When software power-down is asserted, it

becomes effective only after the end of conversion. In all

power-down modes, the interface remains active and

conversion results may be read. Input overvoltage pro-

tection is active in all power-down modes. The device

returns to normal operation on the first WR falling edge

during a write operation.

For hardware-controlled (FULLPD) power-down, pull

the SHDN pin low. When hardware shutdown is assert-

ed, it becomes effective immediately and the conver-

sion is aborted.

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

conversion 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 a

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 MAX199 down after each conversion without

requiring any start-up time on the next conversion.

Multi-Range (±4V, ±2V, +4V, +2V),

+5V Supply, 12-Bit DAS with 8+4 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