THV3056 Datasheet, PDF (15/32 Pages) THine Electronics, Inc. – 3ch Buck/Boost 2ch CP 1ch HVLDO 1ch LVLDO Controller

THV3056_Rev.2.00_E
● Soft Start
THV3056 has Soft Start circuit to prevent high inrush current of the DC/DC converter during start up. SS pins are
internally connected to 1uA constant current source and NMOS pull-down transistor. Soft Start time is set by the external
capacitor connected between each SS pins and GND.
Pull-down transistor is in the On state and the voltage on SS pins are set at Gnd level, until System UVLO or UVLO is
released. On/Off control on each channels are available by connecting SS pins to the external open-drain driver. (See
Figure 3)
Error amplifier has three inputs of PMOS transistor, one inverting and the others non-inverting. One of non-inverting
inputs is connected to SS pin and the other is connected to internal reference voltage. The reference voltage is 1.2V for ch-
1 and ch-3, 0.85V for ch-2. The voltage on SS pin gradually rises up from Gnd level and then exceeds the reference volt-
age. The lower voltage one is active between two non-inverting inputs using PMOS transistors. Thus the input from SS pin
is active if the voltage is under 1.2V for ch-1 and ch-3, 0.85V for ch-2. Also the input from internal reference voltage is
active if the voltage on SS pin exceeds 1.2V for ch-1 and ch-3, 0.85 for ch-2.
During Soft Start operation, SS pin is active and the DC/DC converter operates at the voltage on SS pin as the reference
voltage. The gradual voltage increase on SS pin is equivalent to the gradual increase on the reference voltage and output
voltage. Soft Start operation is completed when the voltage on SS pin reaches to the internal reference voltage.
Soft start time, Tss, is calculated as following :
When C ss ≒ 0.01uF , Tss ≒ 1 2m s for ch-1 and ch-3/ Tss ≒ 8 .5m s for ch-2.
Tss1,3 ≒
1.2
110^6
×
= 1.2×10⁶ ×Css (sec)
Tss2 ≒
0.85
1  10 ^6
×
= 0.85×10⁶ ×Css (sec)
Different from DTC type, this type of soft start provides a natural rising-up waveform without overshooting. Soft Start
time is defined only by the external capacitor and output voltage rises up in proportion to the gradual voltage rising up on
SS pin. Also the sequence setting is easy because it doesn’t depend on the load current fluctuation at the power on, and that
facilitate the setting of sequences. Please note that the power on during output short circuit causes instant maximum duty
operation, because the control circuit recognize that the output voltage doesn’t reach to the user defined set voltage.
(See Functional Description “DTC” for detail)
● PG
PG pins are open-drain outputs of NMOS pull-down transistor. When the power supply is turned On, NMOS transistor is
On and the voltage on PG pin is Gnd level. When the voltage on SS2 pin reaches to approximately 1V for ch-2, SS3 pin
reaches 1.35V for ch-3, NMOS transistor is turned Off. When PG pins are connected to external control pins, resistor con-
nection pins must be set according to the power supply voltage.
　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 Table 1 PG Resistor Connection
Power Supply Voltage
under 5.5V
higher than 5.5V
Resistor Connection pin
PUP_PG
VREG5
Connecting PG pins to VCC through approximately 100kohm pull-up resistor, the output voltage on PG pins rises up to
High level when output voltage reaches more than 90% of user defined voltage. Those output signals can be utilized for
other external circuits, but do not connect to the pull-up resistor to the higher voltage than VREG5.
Copyright©2010 THine Electronics, Inc.
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THine Electronics, Inc.