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MAX1358B
16-Bit, Data-Acquisition System with ADC, DACs,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
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61
With the SLEEP or
SLEEP function deasserted on
UPIO, clear the SHDN bit by writing to the normal-
mode register address control byte.
With the SLEEP or
SLEEP function deasserted,
assert WU or
WU (wake-up) function on UPIO.
With the SLEEP or
SLEEP function deasserted, the
day alarm triggers.
Wake-Up
A wake-up event, such as an assertion of a UPIO con-
figured as WU or a time-of-day alarm causes the
MAX1358B to exit sleep mode, if in sleep mode. A
wake-up event in normal mode results only in a wake-up
event being recorded in the STATUS register.
RESET
The
RESET output pulls low for any one of the following
cases: power-on reset, DVDD monitor trips and
RSTE = 0, watchdog timer expires, crystal oscillator is
attached, and 32kHz clock not ready.
The
RESET output can be turned off through the RSTE
bit in the PS_VMONS register, causing DVDD low sup-
ply voltage events to issue an interrupt or poll through
the LDVD status bit. This allows brownout detection
Cs that operate with DVDD < 1.8V.
Driving UPIO Outputs to AVDD Levels
UPIO outputs can be driven to AVDD levels in systems
with separate AVDD and DVDD supplies. Disable the
charge-pump doubler by setting CPE = 0 in the
PS_VMONS register, and connect the system’s analog
supply to AVDD and CPOUT. Setting UPIO outputs to
drive to CPOUT results in AVDD-referenced logic levels.
Supply Voltage Measurement
The AVDD supply voltage can be measured with the
ADC by reversing the normal input and reference sig-
nals. The REF voltage is applied to one multiplexer
input, and AGND is selected in the other. The AVDD
signal is then switched in as the ADC reference voltage
and a conversion is performed. The AVDD value can
then be calculated directly as:
VAVDD = (VREF x Gain x 65,536)/N
where VREF is the reference voltage for the ADC, Gain
is the PGA gain before the ADC, and N is the ADC
result. Note the AVDD voltage must be greater than the
gained-up REF voltage (AVDD > VREF x Gain). This
measurement must be done in unipolar mode.
0000 0000 0000 0000
0000 0000 0000 0001
0000 0000 0000 0010
65,535
65,533
INPUT VOLTAGE (LSB)
B
INA
RY
O
U
TP
UT
CO
DE
1111 1111 1111 1101
1111 1111 1111 1110
1111 1111 1111 1111
1 LSB =
VREF
(GAIN x 65,536)
0
2
VREF/GAIN
V
REF
/GAIN
13
1111 1111 1111 1100
0000 0000 0000 0011
FULL-SCALE TRANSITION
Figure 20. ADC Unipolar Transfer Function
MAX1358B
DAC A
OUTA
OUTB
REF
DAC B
FBA
FBB
Figure 22. DAC Unipolar Output Circuit
0+1
-1
1000 0000 0000 0000
1000 0000 0000 0001
1000 0000 0000 0010
+32,767
+32,765
INPUT VOLTAGE (LSB)
B
INA
RY
O
U
TP
UT
CO
DE
0111 1111 1111 1101
0111 1111 1111 1110
0111 1111 1111 1111
0000 0000 0000 0000
0000 0000 0000 0001
1111 1111 1111 1111
1 LSB =
VREF
(GAIN x 65,536)
x 2
-32,768
-32,766
VREF/GAIN
V
REF
/GAIN
V
REF
/GAIN
Figure 21. ADC Bipolar Transfer Function