BD9328EFJ_15 Datasheet, PDF (12/23 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9328EFJ
4. Soft Start Function
COMP
ERRAMP
+
+_-
ISS 10µA
↓
SS
C_SS
Figure 24
5. EN Function
V_IN
EN
66 kΩ(typ)
91 kΩ(typ)
R_{REEN N}
EN
ON/OFF
Signal
Figure 25
Datasheet
An adjustable soft-start function to prevent high inrush current
during start-up is available.
The soft-start time is set by the external capacitor connected
to SS pin.
The soft start time is given by
  t_SS s  2.2  C_SS / I _SS
The charge time of C_SS
  t_SS1 s  0.6  C_SS / I _SS
The SS terminal rising time
  t_{SS 2} s  1.6  C_SS / I _SS
Setting C_SS= 0.1µF
t_SS [s]  (0.6  1.6)  0.1 /10  22
[ms]
Please confirm the overshoot of the output voltage and inrush
current in deciding the SS capacitor value.
The EN terminal controls the IC’s shut down.
Leaving EN terminal open shuts down the IC.
To start the IC, the EN terminal should be connected to V_IN or
to another power source.
When the EN voltage exceeds 1.2V (typ), the IC starts
operating.
(Attention)
If the falling edge of EN input is too slow, output chattering
occurs. This may cause large inverse current from output to
input to flow and V_IN voltage to increase, leading to
destruction of the IC. Thus, set the fall time of EN signal within
100µs when controlling the ON/OFF operation of the IC.
This requirement is not needed when EN pin is connected
with VIN and EN is not controlled.
As a recommendation, control EN with an open drain
MOSFET connected as shown on Figure 25.
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TSZ22111・15・001
12/19
TSZ02201-0323AAJ00020-1-2
16.Feb.2015 Rev.003