SC1109 datasheet(14/17 Pages) SEMTECH

14 / 17 page

SYNCHRONOUS PWM CONTROLLER WITH

DUAL LOW DROPOUT REGULATOR

CONTROLLERS

PRELIMINARY - October 16, 2000

SC1109

TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com

Vout

rents are supplied by Cout only, and connections be-

tween Cout and the load must be short, wide copper

areas to minimize inductance and resistance.

5) The SC1109 is best placed over a quiet ground

plane area, avoid pulse currents in the Cin, Q1, Q2

loop flowing in this area. GND should be returned to

the ground plane close to the package and close to

the ground side of (one of) the output capacitor(s). If

this is not possible, the GND pin may be connected to

the ground path between the Output Capacitor(s) and

the Cin, Q1, Q2 loop. Under no circumstances should

GND be returned to a ground inside the Cin, Q1, Q2

loop.

6) BST for the SC1109 should be supplied from the

12V supply, the BST pin should be decoupled directly

to GND by a 0.1

µF ceramic capacitor, trace lengths

should be as short as possible. If a 12V supply is not

available, a classical boot strap method could be im-

plemented to achieve the upper Mosfet’s gate drive.

7) The Phase connection should be short .

8) Ideally, the grounds for the two LDO sections

should be returned to the ground side of (one of) the

output capacitor(s).

Currents in various parts of the power section

SC1109 Datasheet(PDF) 14 Page - Semtech Corporation