Datasheet

1.25V
STANDBY
0.45V
SHUTDOWN
VIN
5.0V
UVLO
R1
R2
22 PA
LM25037
R
1
=
22 PA
R
2
=
1.25 x R
1
V
PWR
- 1.25
V
HYS
-
20 x 10
-3
x V
PWR
1.25
LM25037, LM25037-Q1
www.ti.com SNVS572D –JULY 2008–REVISED MARCH 2013
UVLO DIVIDER SELECTION
A dedicated comparator connected to the UVLO pin detects an input under-voltage condition. When the UVLO
pin voltage is below 0.45V, the LM25037 controller is in a low current shutdown mode. For a UVLO pin voltage
greater than 0.45V but less than 1.25V, the controller is in standby mode with VCC and REF regulators active
but no switching. Once the UVLO pin voltage is greater than 1.25V, the controller is fully enabled. When the
UVLO pin voltage rises above the 1.25V threshold, an internal 22 µA current source as shown in Figure 27, is
activated thus providing threshold hysteresis. The 22 µA current source is deactivated when the voltage at the
UVLO pin falls below 1.25V. Resistance values for R1 and R2 can be determined from the following equations:
(7)
Where V
PWR
is the desired turn-on voltage and V
HYS
is the desired UVLO hysteresis at V
PWR
.
Figure 27. Basic UVLO Configuration
For example, if the LM25037 is to be enabled when V
PWR
reaches 33V, and disabled when V
PWR
decreases to
30V, R1 should be 113 kΩ, and R2 should be 4.42 kΩ. The voltage at the UVLO pin should not exceed 7V at
any time. Be sure to check both the power and voltage rating (0603 resistors can be rated as low as 50V) for the
selected R1 resistor. To maintain the UVLO threshold accuracy, a resistor tolerance of 1% or better is
recommended.
Remote control of the LM25037 operational modes can be accomplished with open drain device(s) connected to
the UVLO pin as shown in Figure 28.
Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links: LM25037 LM25037-Q1