THV3543_Rev.1.00_E
Functional Description
ꢀ
System UVLO
THV3543 has builtꢀin UVLO (Under Voltage Lockout) circuit to prevent lowꢀvoltage input malfunction. The internal
specified threshold voltage is 3.5V, the release voltage is 5.46V. When input power supply voltage (Vin) reaches the
UVLO release voltage (5.46V), the device starts the soft start operation and output voltage (Vo) gradually rises up to
the regular voltage. When the input power supply voltage (Vin) drops below 3.5V, UVLO stops switching operation
immediately and starts discharging soft start. Accordingly, the output voltage (Vo) drops (See Figure 1).
5.46V
Vin
3.50V
Stop
Stop
switching
Operating
Operating
Vo
Figure 1. UVLO Operation Example
The UVLO threshold voltage also can be set optionally by applying divided Vin by an external resistance to
SYSUVLO pin (See Figure 2). Please use external resistance of enough lower value than the internal resistance. The
System UVLO threshold voltage is given by the following formulas.
R1+ R2
System UVLO Release Voltageꢀ=1.56×
R2
R1+ R2
System UVLO Detection Voltage(Lower Limit Voltage of Operation)ꢀ=1.0×
R2
Vin
VCC
500k
R1
SYSUVLO
UVLO
COMP
R2
200k
Figure 2. System UVLO Setting Circuit
THine Electronics, Inc.
Copyright© 2011 THine Electronics, Inc.
11/19
THINE [ THINE ELECTRONICS, INC. ]
