BD9B400MUV Datasheet, PDF (17/34 Pages) Rohm – Integrated MOSFET Single Synchronous Buck DC/DC Converter

BD9B400MUV
(2) Enable Control
The IC shutdown can be controlled by the voltage applied to the EN terminal. When VEN reaches 2.0 V(Typ), the
internal circuit is activated and the IC starts up. To enable shutdown control with the EN terminal, the shutdown
interval (Low level interval of EN) must be set to 100 µs or longer. Startup by EN must be at the same time or after
the input of power supply voltage.
VEN
EN terminal
VENH
VENL
0
t
VOUT
Output setting voltage
0
t
Soft start 1 msec
(typ.)
Figure 43. Start Up and Down with Enable
(3) Power Good
When the output voltage reaches more than 80% of the voltage setting, the open drain NMOSFET, internally
connected to the PGD terminal, turns off and the PGD terminal turns to Hi-z condition. Also when the output voltage
falls below 70% of voltage setting, the open drain NMOS FET turns on and PGD terminal pulls down with 100Ω.
Connecting a pull up resistor (10KΩ to 100KΩ) is recommended.
EN
V_OUT
Voltage Setting×80%
Voltage Setting×70%
PGD
Figure 44. Power Good Timing Chart
(4) Soft Start
When EN terminal is turned High, Soft Start operates and output voltage gradually rises. With the Soft Start Function,
over shoot of output voltage and rush current can be prevented. Rising time of output voltage when SS terminal is
open is 1msec (Typ). Capacitor connected to SS terminal makes rising time more than 1msec. Please refer to page
23 for the method of setting rising time.
EN
V_OUT
0.8V×90%
0.8V
FB
1m sec(typ.)
※When SS terminal is Open
Figure 45. Soft Start Timing Chart
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