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BL8091

Switching waveform Vin=5V, Iout=0

Switching waveform Vin=5V, Iout=2A

FUNCTIONAL DECRIPTIONS

Loop Operation

The BL8091 is a wide input range, high-efficiency, DC-to-DC step-down switching regulator, capable of delivering up to

2A of output current, integrated with a 110m synchronous MOSFET, eliminating the need for external diode. It uses a

PWM current-mode control scheme. An error amplifier integrates error between the FB signal and the internal reference

voltage. The output of the integrator is then compared to the sum of a current-sense signal and the slope compensation

ramp. This operation generates a PWM signal that modulates the duty cycle of the power MOSFETs to achieve regulation

for output voltage.

Current Limit

There is a cycle-by-cycle current limit on the high-side MOSFET of 3A(typ). When the current flowing out of SW exceeds

this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. Unlike the traditional method of

current limiting by limiting the voltage at the compensation pin, which usually has large variation due to duty cycle

variance, this type of peak current limiting scheme provides a relatively more accurate limit for output current, thereby

lowering the requirements for system design.

Light Load Operation

Traditionally, a fixed current mode constant frequency PWM DC-DC regulator always switches even when the output

load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due to the finite

RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and efficiency is therefore very

low. BL8091 employs a proprietary control scheme that improves efficiency in this situation by enabling the device into a

power save mode during light load, thereby extending the range of high efficiency operation.

Faster Transient Response

Normally, people use 3.3nF and 5.6Kohm RC for compensation to keep the loop stable. However, if one needs to have

faster load transient response, 3.3nF and 8.5Kohm is recommended.

VIN

VOUT

SW

I_L

VIN

VOUT

SW

I_L