Datasheet

UVLO
LM5032
1.25V
20 PA
Max. Duty
Cycle Limiter
R1
R2
V
PWR
Enable V
CC
Regulator
and Output Drivers
R2 =
1.25 x R1
V
PWR
- 1.25
VCC
8V - 15V
LM5032
C1
VIN
8V-15V
Start-up
Voltage
V
PWR
VIN
VCC
8V - 15V (from
power stage)
C1
LM5032
9V
0.1
LM5032
www.ti.com SNVS344A –MARCH 2005–REVISED APRIL 2013
Figure 23. Start-up Regulator for V
PWR
>100V
Figure 24. Bypassing the Internal Start-up Regulator
UVLO
The under-voltage lockout threshold (UVLO) is internally set at 1.25V at the UVLO pin. With two external
resistors as shown in Figure 25, the LM5032 is enabled when V
PWR
exceeds the programmed threshold voltage.
When V
PWR
is above the threshold, the internal 20 µA current source is enabled to raise the voltage at the UVLO
pin, providing hysteresis. R1 and R2 are determined from the following equations:
R1 = V
HYS
/20 µA (3)
(4)
where V
HYS
is the desired UVLO hysteresis at V
PWR
, and V
PWR
in the second equation is the turn-on voltage. For
example, if the LM5032 is to be enabled when V
PWR
reaches 20V, and disabled when V
PWR
is decreased to 17V,
R1 calculates to 150 kΩ, and R2 calculates to 10 kΩ. The voltage at UVLO should not exceed 6V at any time.
Figure 25. UVLO Circuit
The LM5032 can be remotely shutdown by taking the UVLO pin below 1.25V with an external open collector or
open drain device, as shown in Figure 26. The outputs, and the V
CC
regulator, are disabled, and the LM5032
enters a low power mode. To shut down one regulator without affecting the other, see the Soft-start section.
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