Datasheet

Datasheet

10/21

TSZ02201-0323AAJ00300-1-2

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

12. Nov. 2012 Rev.001

www.rohm.com

TSZ22111・15・001

BD93291EFJ

●Explanation of Operation

The BD93291EFJ is a dual synchronous buck converter incorporating ROHM’s proprietary H

When VOUT1 and VOUT2 drop due to a rapid load change, the system quickly restores VOUT1 and VOUT2 by increasing

the frequency.

1. H

1-1. Normal Operation

When FB falls below the threshold voltage (REF), a drop is detected, activating the H

f

1

V

V

Ton

IN

OUT





[sec]

(1)

HG (Gate of High side MOSFET) output is determined by the formula (1). LG (Gate of Low side MOSFET) output operates

until FB voltage falls below REF voltage after HG becomes OFF. OFF time is restricted by MIN OFF Time ( VOUT1 :

200nsec (typ.), VOUT2 : 50nsec (typ.) ).

Hence, BD93291EFJ runs with a constant on-time by using the input and output voltage to set the internal on-time timer.

1-2. VOUT drops due to a rapid load change

When FB (VOUT) drops due to a rapid load change and the voltage remains below REF, the system quickly restores VOUT

by shortening OFF time of HG (increasing the frequency), improving transient response as shown Figure 22 (b).

FB

REF

HG

Io

LG

FB

REF

HG

LG

Figure 22. H

(a) Normal operation

(b) Rapid load change