BD9123MUV_14 Datasheet, PDF (11/28 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9123MUV
Datasheet
2. Description of Functions
(1) Soft-Start Function
When EN terminal is shifted to “High” activates a soft-starter to gradually establish the output voltage with the current
being limited during startup. It prevents an overshoot of output voltage and an inrush current.
The slope of input signal is different and the soft start time is different depending on the value offset output voltage.
When set to 1V ,tSS=1msec(Typ)
V_CC,EN
V_OUT
1.2V
0.85V
tSS
tSS’
[ms]
Figure 25. Soft-Start Action
(2) Shutdown Function
When EN terminal is shifted to “Low”, the device turns to Standby Mode, and all the functional blocks including
reference voltage circuit, internal oscillator and drivers are turned to OFF. Circuit current during standby is 0µA(Typ).
(3) UVLO Function
It detects whether the input voltage supplied is sufficient to secure the output voltage of this IC. A hysteresis of 50mV
(Typ) is designed to prevent output chattering.
Hysteresis 50mV
Vcc
EN
VOUT
Standby Mode
tss
Soft start
Operating Mode
tss
tss
Standby
Mode
Standby
Operating Mode Mode
Operating Mode
Standby Mode
UVLO
UVLO
EN
UVLO
Figure 26. Soft-Start, Shutdown, UVLO Timing Chart
(4) PGOOD Function
When the output voltage falls below 75% (Typ) of a set value, the output of an Open-Drain PGOOD pin is turned OFF. A
hysteresis width of 15% (Typ) is designed to prevent output chattering.
VOUT
90%
75%
PGOOD
The hysteresis width
tGP
Figure 27. PGOOD Timing Chart
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02.Oct.2014 Rev.002