BD9109FVM-LB
Description of Block – continued
・SLLMTM (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
SLLMTM
②
50
①
①improvement by SLLMTM system
PWM
②improvement by synchronous rectifier
0
0.001
0.01
0.1
1
Output current Io[A]
Figure 5. Efficiency
SENSE
Current
Comp
VOUT
RESET
R
S
Q
IL
Level
Shift
FB
SET
Driver
Logic
VOUT
Gm Amp.
SW
Load
OSC
ITH
Figure 6. Diagram of current mode PWM control
PVCC
SENSE
PVCC
Current
Comp
Current
SENSE
Comp
FB
FB
SET
SET
GND
GND
GND
GND
RESET
SW
RESET
GND
SW
GND
IL
IL(AVE)
IL
0A
VOUT
VOUT
VOUT(AVE)
VOUT(AVE)
Not switching
Figure 8. SLLMTM switching timing chart
Figure 7 . PWM switching timing chart
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TSZ22111 • 15 • 001
TSZ02201-0J4J0AJ00600-1-2
21.Feb.2014 Rev.002
4/20
ROHM [ ROHM ]
