Low-Power, 8-Channel,
Serial 10-Bit ADC
Table 5. Worst-Case Power-Up Delay Times
Reference
Buffer
Enabled
Enabled
Enabled
Enabled
Disabled
Disabled
Reference-
Buffer
Compensation
Mode
Internal
Internal
External
External
VREF
Capacitor
(µF)
4.7
4.7
Power-
Down
Mode
Fast
Full
Fast
Full
Fast
Full
Power-Up
Delay
(sec)
5µ
300µ
See Figure 14c
See Figure 14c
2µ
2µ
Maximum
Sampling
Rate (ksps)
26
26
133
133
133
133
Table 6. Software Shutdown and Clock
Mode
PD1 PD0 Device Mode
1
1
External Clock Mode
1
0
Internal Clock Mode
0
1
Fast Power-Down Mode
0
0
Full Power-Down Mode
tors that will not discharge more than 1/2LSB while shut
down. In shutdown, the capacitor has to supply the cur-
rent into the reference (1.5µA typ) and the transient cur-
rents at power-up.
Figures 12a and 12b illustrate the various power-down
sequences in both external and internal clock modes.
Software Power-Down
Software power-down is activated using bits PD1 and
PD0 of the control byte. As shown in Table 6, PD1 and
PD0 also specify the clock mode. When software shut-
down is asserted, the ADC will continue to operate in
the last specified clock mode until the conversion is
complete. Then the ADC powers down into a low quies-
cent-current state. In internal clock mode, the interface
remains active and conversion results may be clocked
out while the MAX192 has already entered a software
power-down.
The first logical 1 on DIN will be interpreted as a start
bit, and powers up the MAX192. Following the start bit,
the data input word or control byte also determines
clock and power-down modes. For example, if the DIN
word contains PD1 = 1, then the chip will remain pow-
ered up. If PD1 = 0, a power-down will resume after
one conversion.
Table 7. Hard-Wired Shutdown and
Compensation Mode
SHDN
State
Device
Mode
Reference-Buffer
Compensation
1
Floating
0
Enabled
Internal Compensation
Enabled
External Compensation
Full Power-Down N/A
Hardware Power-Down
The SHDN pin places the converter into the full
power-down mode. Unlike with the software shutdown
modes, conversion is not completed. It stops coinci-
dentally with SHDN being brought low. There is no
power-up delay if an external reference is used and is
not shut down. The SHDN pin also selects internal or
external reference compensation (see Table 7).
Power-Down Sequencing
The MAX192 auto power-down modes can save con-
siderable power when operating at less than maximum
sample rates. The following discussion illustrates the
various power-down sequences.
Lowest Power at up to 500
Conversions/Channel/Second
The following examples illustrate two different
power-down sequences. Other combinations of clock
rates, compensation modes, and power-down modes
may give lowest power consumption in other applica-
tions.
Figure 14a depicts the MAX192 power consumption for
one or eight channel conversions utilizing full
power-down mode and internal reference compensa-
tion. A 0.01µF bypass capacitor at REFADJ forms an
16 ______________________________________________________________________________________