Datasheet

R2 x 2.5V
R3 =
V
UVL
± 2.5V
5 µA
V
UV(HYS)
R2 =
V
UVH
- V
UVL
5 µA
=
www.ti.com Under-Voltage Detector
Figure 5. Efficiency at 200 kHz
6 Under-Voltage Detector
The under voltage detector can be used to monitor the input voltage, or any other system voltage as long
as the voltage at the UV pin does not exceed its maximum rating. On this evaluation board, the input
voltage is monitored via resistors R2 and R3.
An appropriate pull-up voltage less than 10 volts must be connected to test point TP2-UVO on this
evaluation board. R4 is the pull-up resistor for the UVO output. The under-voltage status can then be
monitored at the TP3-Status test point.
On this evaluation board the UVO output switches low when the input voltage exceeds 12V, and it
switches high when the input voltage is less than 11V. If it is desired to change the thresholds, the
equations for determining the resistor values are:
(6)
(7)
where, V
UVH
is the upper threshold at VIN, and V
UVL
is the lower threshold. The threshold at the UV pin is
2.5V.
The UVO output is high when the VCC voltage is below its UVLO threshold, or when the LM34923 is
shutdown by grounding the TP1-SD test point, regardless of the voltage at the UV pin.
5
SNVA482A–May 2011–Revised April 2013 AN-2147 LM34923 Evaluation Board
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