BD9528AMUV Datasheet, PDF (13/30 Pages) Rohm – High Performance Regulators for PCs Main Power Supply for Notebook PCs(With Built-in Linear Regulator)

BD9528AMUV
Technical Note
●Explanation of Operation
The BD9528AMUV is a 2ch synchronous buck regulator controller incorporating ROHM’s proprietary H³REG CONTROLLA
control system. Because controlling of output voltage by a comparator, high response is realized with not relying on the
switching frequency. And, when VOUT drops due to a rapid load change, the system quickly restores VOUT by extending the
TON time interval. Thus, it serves to improve the regulator’s transient response. Activating the Light Load Mode will also
exercise Simple Light Load Mode (SLLM) control when the load is light, to further increase efficiency.
VIN
H³Reg^TM control
Comparator for
output voltage control
FB
Internal
reference
voltage
REF
Vout/Vin
Circuit
A
B
Transient
Circuit
HG
SW
Driver
LG
VOUT
(Normal operation)
FB
REF
HG
LG
(VOUT drops due to a rapid load change)
FB
REF
Io
tON +α
HG
LG
When FB falls to a reference voltage (REF),
the drop is detected, activating the H³REG CONTROLLA
system.<Route A>
tON==
VOUT
1
×
[sec]・・・(1)
VIN
f
HG output is determined by the formula above.
After the status of HG is OFF, LG go on outputting until
output voltage become FB=REF.
When VOUT drops due to a rapid load change, and the
voltage remains below reference voltage after the
programmed tON time interval has elapsed (Output of a
comparator for output voltage control =H), the system
quickly restores VOUT by extending the tON time,
improving the transient response.<Route B> After VOUT
restores (FB=REF), HG turns to be OFF, and it goes back
to a normal operation.
(when VIN drops)
VIN
tON1
HG
LG
FB
REF
tOFF1
tON2
tON3
tOFF2
tOFF3
tON4
tOFF4=tOFF3
H₃Reg^TM
tON4+α
tOFF4=tOFF3
FB=REF
Output voltage drops
If VIN voltage drops because of the battery voltage fall, ontime tON and offtime tOFF is determined by the following formula:
tON=VOUT/VIN×I/f and tOFF=(VIN-VOUT)/VIN×f so that tON lengthen and tOFF shorten to keep output voltage constant.
However, if VIN still drops and tOFF equals to tminoff (tminoff:Minimum OFF time, regulated inside IC) , because tOFF
cannot shorten any more, as a result output voltage drops. In H3RegTM system, lengthening tON time than regulated tON
(lengthen tON time until FB＞REF) enables to operate stable not to drop the output voltage even if VIN turns to be low. With
the reason above, it is suitable for 2-cell battery.
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13/29
2011.11 - Rev.A