BD9123MUV_11 Datasheet, PDF (8/18 Pages) Rohm – Output 1.5A or Less High-efficiency Step-down Switching Regulator with Built-in Power MOSFET

BD9123MUV
Technical Note
●Description of operations
・Soft-start function
EN terminal shifted to “High” activates a soft-starter to gradually establish the output voltage with the current limited during
startup, by which it is possible to prevent an overshoot of output voltage and an inrush current.
The inclination of standing up is different and the soft start time is different because of constancy depending on the value
offset output voltage. When 1V settiing it, it is Tss=1msec(Typ.)
VCC,EN
VOUT
1.2V
0.85V
Tss
Tss’
[ms]
Fig.28 Soft start action
・Shutdown function
With EN terminal shifted to “Low”, the device turns to Standby Mode, and all the function blocks including reference
voltage circuit, internal oscillator and drivers are turned to OFF. Circuit current during standby is 0µA(Typ.).
・UVLO function
Detects whether the input voltage sufficient to secure the output voltage of this IC is supplied. And the hysteresis width of
50mV (Typ.) is provided to prevent output chattering.
Hysteresis 50mV
Vcc
EN
VOUT
Standby mode
Tss
Soft start
Operating mode
Tss
Standby
mode
Standby
Operating mode mode
Tss
Operating mode
Standby mode
UVLO
UVLO
EN
UVLO
Fig.29 Soft start, Shutdown, UVLO timing chart
・PGOOD function
When the output voltage falls below 75% (Typ.) of a set value, the PGOOD pin of Open-Drain is turned off. And the
hysteresis width of 15% (Typ.) is provided to prevent output chattering.
VOUT
90%
75%
PGOOD
The hysteresis width
TGP
Fig.30 PGOOD timing chart
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8/17
2011.01 - Rev.A