BD9329AEFJ_15 Datasheet, PDF (12/23 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9329AEFJ
4. Soft Start Function
COMP
ERRAMP
+
+_-
↓ ^{ISS 10µA}
↓ _SS
CSS
Figure 24
5. EN Function
VIN
EN
66 kΩ(typ)
91 kΩ(typ)
R_RE_EN_N
EN
ON/OFF
Signal
Figure 25
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 CSS
[ ] 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 CSS= 0.1µF
t_SS [s] = (0.6 + 1.6) × 0.1µ /10µ = 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 shutdown.
Leaving EN terminal open shuts down the IC.
To start the IC, EN terminal should be connected to VIN or other
power source output.
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 VIN 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
TSZ02201-0323AAJ00010-1-2
16.Feb.2015 Rev.003