LTC2933
22
2933fa
For more information www.linear.com/LTC2933
Power Supply
The LTC2933 is powered from any one of the voltage
monitoring inputs V1 to V4. A virtual diode-OR scheme
selects the highest supply voltage. V1 to V4 should be
driven by a low impedance source for proper operation of
the diode-OR circuit. The LTC2933 generates a regulated
3.3V supply on the V
DD33
pin. A 100nF external capacitor
from the highest supply voltage pin (V1 to V4) to GND is
required in order to decouple any supply noise. A 220nF
external capacitor from V
DD33
to GND is required to properly
compensate the internal voltage regulator.
Power-Up Condition
When power is applied such that at least one of the supply
inputs V1 to V4 exceeds 3.4V, the part turns on and the
EEPROM contents are loaded into the volatile operating
memory. This operation typically takes less than 200µs.
Power-Down Condition
If all of the supply inputs, V1 to V4, drop below 3.4V, the
internal regulator will start to fall out of regulation. Once
V
DD33
falls below the internal undervoltage lockout voltage,
the GPIO outputs will pull low. See the Typical Performance
Characteristics section.
Voltage Threshold Programming
The V1 input has a high range that is based on a full scale
of 2.25V to 15V. The 8-bit programming step size is 50mV.
Some of these thresholds are outside of the 14V abs max
voltage rating of the V1 input. On the high range, threshold
accuracy below 2.5V and above 13.9V is not specified, but
the thresholds are reachable.
The command byte for the voltage threshold can be cal
-
culated for the V1 high range with the following equation:
Command Byte = ROUND [20 • (V
TH
– 2.25)]
Inputs from V1 through V6 have a medium range that is
based on a full scale of 0.9V to 6V. The 8-bit program
-
ming step size is 20mV. On the medium range, threshold
accuracy below 1V
and above 5.8V is not specified, but
the thresholds are reachable.
The command byte for the voltage threshold can be cal
-
culated for the V1 to V6 medium range with the following
equation:
Command Byte = ROUND [50 • (V
TH
– 0.9)]
Inputs from V2 through V6 have a low range that is based
on a full scale of 0.45V to 3V. The 8-bit programming step
size is 10mV. On the low range, threshold accuracy below
0.5V is not specified, but the thresholds are reachable.
The command byte for the voltage threshold can be
calculated for the V2 to V6 low range with the following
equation:
Command Byte = ROUND [100 • (V
TH
– 0.45)]
Inputs from V2 through V6 have a precision range that
is based on a full scale of 0.18V to 1.2V. The 8-bit pro
-
gramming step size is 4mV. On the low range, threshold
accuracy below 0.2V
is not specified, but the thresholds
are reachable.
The command byte for the voltage threshold can be
calculated for the V2 to V6 precision range with the fol
-
lowing equation:
Command Byte = ROUND [250 • (V
TH
– 0.18)]
Although all six channels have built-in glitch immunity,
100nF bypass capacitors on the V1 to V4 inputs are rec
-
ommended because the largest V1 to V4 voltage is also
the power supply for the device.
Unused Channels
The user must connect all unused channel inputs to
ground , program their configuration words (V
n
_CONFIG)
to 0x01C0, and program their thresholds (V
n
_THR) to
0x0000 in order to avoid false faults.
Auxiliary Comparators
Two additional auxiliary comparators can be connected
to the general purpose inputs with either their inverting
or their noninverting input while the other input internally
connects to a 0.5V reference voltage. These low offset, low
drift comparators can be used for additional monitoring
purposes.
applicaTions inForMaTion
