
TPS31xxExx, TPS31xxH20, TPS31xxK33
ULTRALOW SUPPLY-CURRENT/SUPPLY-VOLTAGE SUPERVISORY CIRCUITS
SLVS363
–
AUGUST 2001
17
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
The TPS310x family has a quiescent current in the 1-
μ
A to 2-
μ
A range. When RESET, triggered by the voltage
monitored at VDD, is active, the quiescent current increases to about 20
μ
A (see electrical characteristics).
In some applications it is necessary to minimize the quiescent current even during the reset period. This is
especially true when the voltage of a battery is supervised and the RESET is used to shut down the system or
for an early warning. In this case the reset condition will last for a longer period of time. Especially when the
battery is discharged, the current drawn from the battery should almost be zero.
For this kind of applications the TPS3103 or TPS3106 are a good fit. To minimize current consumption it must
be assured to select a version where the threshold voltage is lower than the voltage monitored at VDD. The
TPS3106 has two reset outputs. One output (RSTVDD) is triggered from the voltage monitored at VDD. The
other output (RSTSENSE) is triggered from the voltage monitored at SENSE. In the application shown in
Figure 13, the TPS3106E09 is used to monitor the input voltage of two NiCd or NiMH cells. The threshold
voltage (V
(th)
= 0.86 V) was chosen as low as possible to ensure that the supply voltage is always higher than
the threshold voltage at VDD. The voltage of the battery is monitored using the SENSE input. The voltage divider
was calculated to assert a reset using the RSTSENSE output at 2 x 0.8 V = 1.6 V.
R1
R2
Vtrip
Vit(s)
1
Where:
Vtrip is the voltage of the battery at which a reset is asserted
Vit(s) is the threshold voltage at SENSE = 0.551 V.
R1 was chosen for a resistor current in the 1-
μ
A range.
With Vtrip = 1.6 V:
R1
≈
1.9
×
R2
R1 = 820 k, R2 = 430 k
TPS3106E09DBV
MR
SENSE
GND
R1
R2
VDD
RSTVDD
RSTSENSE
R3
2 Cell
NiMH
Reset Output
Figure 13. Battery Monitoring With 3-
μ
A Supply Current for Device and Resistor Divider