MAX199
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
FS -
3
/
2
LSB
1 LSB =
FULL-SCALE
TRANSITION
123
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
2FS
4096
Figure 11. Bipolar Transfer Function
