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TSZ02201-0J4J0AJ00580-1-2

© 2013 ROHM Co., Ltd. All rights reserved.

21.Feb.2014 Rev.002

www.rohm.com

TSZ22111

• 15 • 001

BD9161FVM-LB

Description of Block

BD9161FVM-LB is a synchronous rectifying step-down switching regulator that achieves faster transient response by

employing current mode PWM control system.

It utilizes switching operation in PWM (Pulse Width Modulation) mode for

heavier load, while it utilizes SLLM

○Current mode PWM control

Synthesizes a PWM control signal with a inductor current feedback loop added to the voltage feedback.

・PWM (Pulse Width Modulation) control

The oscillation frequency for PWM is 1 MHz.

SET signal form OSC turns ON a P-channel MOS FET (while a

The current comparator (Current Comp)

control signal (FB), and issues a RESET signal if both input signals are identical to each other, and turns OFF the

P-channel MOS FET (while a N-channel MOS FET is turned ON) for the rest of the fixed period.

The PWM control

repeats this operation.

Offers fast transient response with current mode control system.

Voltage drop due to sudden change in load was reduced by about 50%.

Figure 4. Comparison of transient response

・SLLM

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.

98mV

40mV

Figure 5. Efficiency

0.001

0.01

0.1

1

0

50

100

①

②

PWM

SLLM

TM

①inprovement by SLLM

②improvement by synchronous rectifier