BD9111NV_14 Datasheet, PDF (8/25 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9111NV
Datasheet
Application Information
1. Operation
BD9111NV is a synchronous step-down switching regulator that achieves fast transient response by employing current
mode PWM control system. It utilizes switching operation in PWM (Pulse Width Modulation) mode for heavier load, and
operates in SLLM^TM (Simple Light Load Mode) operation for lighter load to improve efficiency.
(1) Synchronous Rectifier
Integrated synchronous rectification using two MOSFETS reduces power dissipation and increases efficiency when
compared to converters using external diodes. Internal shoot-through current limiting circuit further reduces power
dissipation.
(2) Current Mode PWM Control
The PWM control signal of this IC depends on two feedback loops, the voltage feedback and the inductor current
feedback.
(a) PWM (Pulse Width Modulation) Control
The clock signal coming from OSC has a frequency of 1Mhz. When OSC sets the RS latch, the P-channel
MOSFET is turned on and the N-channel MOSFET is turned off. The opposite happens when the current
comparator (Current Comp) resets the RS latch i.e. the P-channel MOSFET is turned OFF and the N-channel
MOSFET is turned on. Current Comp’s output is a comparison of two signals, the current feedback control signal
“SENSE” which is a voltage proportional to the current IL, and the voltage feedback control signal, FB.
(b) SLLM^TM (Simple Light Load Mode) Control
When the control mode is shifted from heavier load to lighter load or vice versa, the switching pulse is designed to
turn OFF with the device held operating in normal PWM control loop. This allows linear operation without voltage
drop or deterioration in transient response during sudden load changes.
Although the PWM control loop continues to operate with a SET signal from OSC and a RESET signal from Current
Comp, it is designed such that the RESET signal is kept constant when shifted to the light load mode where the
switching is turned OFF and the switching pulses disappear. Activating the switching discontinuously reduces the
switching dissipation and improves efficiency.
VOUT
SENSE
Current
Comp
RESET
Level
RQ
Shift _FB
Gm Amp
SET _S
RITH
OSC
Driver
Logic
IL
SW
Load
VOUT
Current
Comp
SET
RESET
SW
IL
VOUT
Figure 19. Diagram of Current Mode PWM Control
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 20. PWM Switching Timing Chart
Not switching
Figure 21. SLLM^TM Switching Timing Chart
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02.Oct.2014 Rev.002