LTC2936
21
2936fa
For more information www.linear.com/LTC2936
applicaTions inForMaTion
Power Supply
The LTC2936 is powered from the V
PWR
input and gen-
erates a regulated 3.3V supply on the V
DD33
. A 100nF
external capacitor from V
PWR
to GND is required in order
to decouple any supply noise. A 100nF external capacitor
from V
DD33
to GND is required to properly compensate
the internal voltage regulator.
To power the LTC2936 directly from an external 3.3V power
supply, connect the V
PWR
and V
DD33
pins together and
connect them to the external 3.3V supply. This mode of
operation is useful for reducing power dissipation.
Power-Up Condition
When power is applied, the part turns on and the EEPROM
contents are loaded into the volatile operating memory.
This operation typically takes less than 200µs.
Voltage Threshold Programming
The medium range is based on a full scale of 0.9V to 6V.
The 8-bit programming 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 medium range with the following equation:
Command Byte = ROUND [50 • (V
TH
– 0.9)]
The low range 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 low range with the following equation:
Command Byte = ROUND [100 • (V
TH
– 0.45)]
The precision range is based on a full scale of 0.18V to
1.2V. The 8-bit programming 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)]
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.
If the tap point on an external resistive divider from an
external voltage, V
TRIP
, to GND (see Figure 2) connects to
the auxiliary comparator input, the trip voltage is:
V
TRIP
= 0.5V • 1+
R2
⎛
⎝
⎜
⎞
⎠
⎟
In a negative voltage application (also shown in Figure 2)
the resistive divider is connected between the negative
voltage being sensed and V
DD33
, and the trip voltage is:
V
TRIP
= 0.5V − 2.8V •
R3
R4
⎛
⎝
⎜
⎞
⎠
⎟
The minimum value for R4 is limited by the V
DD33
current
sourcing capability at:
−
= 2.8kΩ
Figure 2. Auxiliary Comparator Usage
V
TRIP
R2
R1
+
–
+
–
LTC2936
V
DD33
= 3.3V
R3
0.5V 0.5V
LTC2936
R4
+
–
+
–
V
TRIP
