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Datasheet

Datasheet

BM2PXX4 Series

TSZ02201-0F2F0A200070-1-2

28.NOV.2012.Rev.003

© 2012 ROHM Co., Ltd. All rights reserved.

www.rohm.com

TSZ22111・15・001

( 4 ) DCDC driver (PWM comparator, frequency hopping, slope compensation, OSC, burst)

BM2PXX4 is current mode PWM control.

An internal oscillator sets a fixed switching frequency (65kHz typ).

BM2PXX4 is integrated switching frequency hopping function which changes the switching frequency to fluctuate as

shown in Figure 11 below.

The fluctuation cycle is 125 Hz typ.

65

Switching Frequency

[kHz]

69

125 Hz(8ms)

Time

61

62

63

64

66

68

67

500us

Figure 10. Frequency hopping function

Max duty cycle is fixed as 75% (typ) and MIN pulse width is fixed as 400 ns (typ).

With current mode control, when the duty cycle exceeds 50% sub harmonic oscillation may occur.

As a countermeasure to this, BM2PXX4 is built in slope compensation circuits.

BM2PXX4 is built in burst mode circuit and frequency reduction circuit to achieve lower power consumption, when the load

is light.

FB pin voltage is changed by secondary output voltage (secondary load power).

FB pin is monitored, burst mode operation and frequency detection start.

Figure 11 shows the FB voltage, and switching frequency, DCDC operation

・

mode1 : Burst operation

・

mode2: Frequency reduction operation.

・

mode3 : Fixed frequency operation.(operate at the max frequency)

・

mode4 : Over load operation.(detect the over load state and stop the pulse operation)

Figure 11. Switching operation state changes by FB pin voltage