BD9109FVM-LB Datasheet, PDF (4/23 Pages) Rohm – Synchronous Buck Converter Integrated FET

BD9109FVM-LB
Description of Block – continued
・SLLM^TM (Simple Light Load Mode) control
When the control mode is shifted from PWM for heavier load to the one for lighter load or vise versa, the switching
pulse is designed to turn OFF with the device held operated in normal PWM control loop, which allows linear operation
without voltage drop or deterioration in transient response during the mode switching from light load to heavy load or
vise versa.
Although the PWM control loop continues to operate with a SET signal from OSC and a RESET signal from Current
Comp, it is so designed that the RESET signal is held issued if shifted to the light load mode, with which the switching
is tuned OFF and the switching pulses are thinned out under control. Activating the switching intermittently reduces
the switching dissipation and improves the efficiency.
100
SLLM^TM
②
50 _{① PWM}
①improvement by SLLM^TM system
②improvement by synchronous rectifier
0
0.001 0.01
0.1
1
Output current Io[A]
Figure 5. Efficiency
VOUT
SENSE
Current
Comp
RESET
Level
RQ
Shift _FB
Gm Amp.
SET _S
OSC
ITH
Driver
Logic
IL
SW
Load
VOUT
Figure 6. Diagram of current mode PWM control
Current
Comp
SET
RESET
SW
IL
VOUT
PVCC
SENSE
FB
GND
Current
Comp
SET
GND
GND
RESET
SW
IL(AVE)
IL
VOUT(AVE)
VOUT
PVCC
SENSE
FB
GND
GND
GND
0A
VOUT(AVE)
Figure 7 . PWM switching timing chart
Not switching
Figure 8. SLLM^TM switching timing chart
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TSZ02201-0J4J0AJ00600-1-2
21.Feb.2014 Rev.002