BL3406B-2.5V データシートの表示（PDF） - Shanghai Belling Co., Ltd.

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BL3406B-2.5V

1.5 MHz, 800mA Synchronous Buck Converter

Shanghai Belling Co., Ltd. 

BL3406B

1.5 MHz, 800mA Synchronous Buck Converter

Operation

The BL3406B uses a constant frequency,

current mode step-down architecture. Both

the main switch (P-channel MOSFET) and

the synchronous rectifier (N-channel

MOSFET) are integrated internally. This

Step-Down DC-DC Converter can supply

800mA output current over a wide input

voltage range from 2.5V to 5.5V. The over

voltage comparator OVDET guards against

transient overshoots >7.8% by turning the

main switch off and keeping it off until the

fault is removed.

Current Mode PWM Control

Slope compensated current mode PWM

control provides stable switching and cycle-

by-cycle current limit for excellent load and

line responses. During normal operation, the

internal main switch is turned on for a certain

time to ramp the inductor current at each

rising edge of the internal oscillator, and

turned off when the peak inductor current

reaches the controlled value. When the main

switch is off, the synchronous rectifier will be

turned on immediately and stay on until either

the inductor current starts to reverse, as

indicated by the current reversal comparator,

IRCMP, or the beginning of the next clock cycle.

Pulse Skipping Mode Operation

At very light loads, the BL3406B will

automatically enter Pulse Skipping Mode to

increase efficiency, further extending battery

life. In this mode, the control loop skips PWM

pulses while maintaining output in regulation,

and the switching frequency depends on the

load condition. This is a kind of PFM mode

operation.

Dropout Operation

When the input voltage decreases toward the

value of the output voltage, the BL3406B will

keep the main switch on for more than one

switching cycle and increases the duty cycle

(Note 6) until it reaches 100%. The output

voltage then is the input voltage minus the

voltage drop across the main switch and the

inductor. At low input supply voltage, the

RDS(ON) of the P-Channel MOSFET increases,

and the efficiency of the converter decreases.

Caution must be exercised to ensure the heat

dissipated not to exceed the maximum

junction temperature of the IC.

Note 6: The duty cycle D of a step-down converter is

defined as:

D

= TON

×

f OSC

×100% ≈

VOUT

VIN

×100%

where TON is the main switch on time, and fOSC

is the oscillator frequency (1.5MHz).

Short Circuit Protection

The BL3406B has short circuit protection.

When output is shorted to ground, the

oscillator frequency is reduced to prevent the

inductor current from increasing beyond the

PFET current limit. The PFET current limit is

also reduced to lower the short circuit current.

The frequency and current limit will return to

the normal values once the short circuit

condition is removed and the feedback

voltage reaches 0.6V.

Maximum Load Current

The BL3406B will operate with input supply

voltage as low as 2.5V, however the

maximum load current decreases at lower

input voltage due to large IR drop on the

main switch and synchronous rectifier.

PPMIC BU

www.belling.com.cn

7

BL3406B Rev 1.5

Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited

10/2009

©2009 Belling All Rights Reserved

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