THV3056_Rev.2.00_E
● UVP(Under Voltage Protection)
UVP circuit detects abnormal drops of output voltage caused by short circuits or over load.
The internal UVP comparator monitors the output voltage of error amplifiers(FB1,2,3). In the normal operation the
inverting input voltage is approximately 1.2V, same as the non-inverting input connected internally to VREF. The invert-
ing input voltage decreases in proportion to the output voltage drop. If the output voltage drops below the user defined
voltage, the system goes into Max Duty cycle and UVP comparator reports the abnormal operation of DC/DC converter
to SCP circuit. (See Figure 9)
● Short Circuit Protection （SCP Timer Circuit）
SCP shut down the IC operation when the Max Duty operation/OVP operation /abnormal temperature continue for a
longer time than the user defined time. SCP timer circuit has the internal constant source current circuit, a pull-down tran-
sistor and an external capacitor connected between SCP pin and GND. In the normal operation the internal pull-down tran-
sistor is in On state, and SCP pin is held Gnd level. (See Figure 9.)
When UVP comparator detects the output voltage drop, the pull-down transistor connected with SCP pin is turned to Off
and the external capacitor is charged with 1uA constant current. While OVP comparator detects the output voltage rise or
the abnormal temperature is detected continuously, the voltage on SCP pin keep on rising in proportion to the time con-
stant defined by 5uA constant current and the external capacitor. When the voltage on SCP pin reaches to 1.2V, the latch
operates and then all channels stops and goes into shut down mode. (See Figure 10.) The latch state will not be released
until power supply is restarted. The delay time to the latch state can be set by the external capacitance. Also, users can
select SCP timer mode(On/Off) of charge pump by SEL2 pin.(See Table 3.)
The delay time Tscp is given by following :
When Cscp=0.01uF and UVP is activated, the SCP delay time (Tscp) is around 12msec. Also, when OVP or TSD is acti-
vated, Tovp is around 2.4msec.
In the case of UVP,
1.2
110–6
6
----------------
Tscp =
Cscp= 1.210 Cscpsec
In the case of OVP or TSD,
1.2
510–6
5
----------------
Tovp =
Cscp= 2.410 Cscpsec
Note 1) When output short circuit or over load occur, the input power supply voltage (Vin) may decrease according to the
circumstances. UVLO resets SCP timer latch state, so please set the delay time in order that timer latch works earlier than
UVLO operation. Otherwise, the following operation will be repeated:
Output short-circuit → Power-supply voltage decrease (UVLO operation) → Short-circuit current decrease → Power-sup-
ply voltage rise (UVLO release) → Power-supply voltage decrease
Note 2) When UVP timer latch function of charge pump is set to be enable, please be careful to determine the delay time
considering the startup time of charge pumps. (See Figure 11.)
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀTable 3 SEL2 pin Settingꢀꢀ
SEL2 Connection
GND
Startup Sequence
C.P Timer Latch/Active
C.P Timer Latch/Inactive
VREG5
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THine Electronics, Inc.
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