BD9B500MUV Datasheet, PDF (23/34 Pages) Rohm – Integrated MOSFET Single Synchronous Buck DC/DC Converter

BD9B500MUV
3. Soft Start Setting
Turning the EN terminal signal High activates the soft start function. This causes the output voltage to rise gradually
while the current at startup is placed under control. This allows the prevention of output voltage overshoot and inrush
current. The rise time depends on the value of the capacitor connected to the SS terminal.
T_SS = (C _SS × V_FB )/I _SS
C _SS = (I _SS × T_SS )/V_FB
T_SS : Soft Start Time
C _SS : Capacitorconnectedto Soft Start Time Terminal
V_FB : FB Terminal Voltage(0.8V (Typ))
I _SS : Soft Start Terminal Source Current (1.0μA(Typ))
withC _SS = 0.01 [ μF ] ,
T_SS = (0.01 [ μF ] × 0.8 [V])/1.0 [ μF ]
= 8.0 [msec]
Turning the EN terminal signal High with the SS terminal open or with the terminal signal High (no capacitor
connected) causes the output voltage to rise in 1msec (Typ).
4. FB Capacitor
Generally, in fixed ON time control (hysteresis control), sufficient ripple voltage in FB voltage is needed to operate
comparator stably. Regarding this IC, by injecting ripple voltage to FB voltage inside IC it is designed to correspond
to low ESR output capacitor. Please set the FB capacitor within the range of the following expression to inject an
appropriate ripple.
V_OUT
× (1 - ^VOUT
V _IN
)
f _SW × 7.65 × 10 ³
<
C _FB
<
V_OUT
×
(1 - ^VOUT
V _IN
)
f _SW × 3.3 × 10 ³
VIN :Input Voltage
VOUT : Output Voltage
fSW : Switching Frequency
www.rohm.com
© 2016 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
23/30
TSZ02201-0J3J0AJ01280-1-2
25.May.2016 Rev.001