SC420A 데이터 시트보기 (PDF) - Semtech Corporation

부품명

상세내역

일치하는 목록

SC420A

High Speed, Combi-Sense™, Synchronous Power MOSFET Driver for Mobile Applications

Semtech Corporation 

SC420A

POWER MANAGEMENT

Applications Information (Cont.)

COMPONENT SELECTION FOR SC420A APPLICATION:

Top Gate Resistor (Rtg)

High Side MOSFET (LSFET)

The SC420A is usually used for low duty cycle ( ~ 10% )

applications. So the Rds (ON) of the high side MOSFET is

not a parameter of significant importance. A 10 – 25

mÙ Rds for the HSFET is acceptable depending on the

load current. Minimum Qg for the HSFET is important for

component selection. Typical range is 10 – 25 nC.

Low Side MOSFET (LSFET)

TG resistance is not generally required, as Rbst can take

care of the rising edge. We recommend one Rtg for each

HSFET only when the maximum length of the TG trace > 2

inches. Populate with 0 Ω initially.

Boost Diode (Dbst)

Boost Diode as shown in the above figure is required and

should have a very low forward voltage drop. This increases

the amount of charge on Cbst capacitor.

Rds is the critical selection parameter for LSFET. IT should

be as low as possible for reduction of conduction losses

and hence increase efficiency. Typical range is 1 – 3 mÙ.

Rg is another important parameter for LSFET. It should

be as low as possible as this will give better efficiency.

Typical range 0.1 – 2 Ω. Ratio of Qgd/Qgs is third

parameter of consideration.

Delay Capacitor (Cdly)

Delay capacitor is not added in a typical application. This

option is useful to control the delay between the BG falling

and TG rising edges. Cdly is used for very high capacitance

LSFETs to ensure BG is below Vth of the FET before TG

turns on.

As the duty cycle for the application increases, require-

ments for the two FETs become more similar; however,

switching charge will always be more important to the

HSFET since it switches into the full voltage, and the LSFET

always switching into the near zero voltage.

Boost Capacitor (Cbst)

Decoupling capacitors (C1,C3)

These are de-coupling capacitors present in the circuit.

Place as close to SC420A as possible. Typical rating is 1uF/

10V for C1 and 0.1uF /25V for C3.

Boost capacitor is important for SC420A application as

shown in the above figure. It is a good design rule to have

boost capacitance at least 100 X the Cgs for the HSFET.

Boost Resistor (Rbst)

Boost resistance is important and depends on the layout.

We recommend always designing with the resistor as shown

in the above circuit to help minimize EMI when the HSFET

turns on. The value required is layout dependant.

Bottom Gate Resistor (Rbg)

BG resistance is normally not required, but may be needed

for damping for long BG trace runs. We recommend one

Rbg for each LSFET only when the maximum length of the

BG trace is > 1 inch. Populate with 0 Ω initially.

© 2004 Semtech Corp.

11

United States Patent No. 6,441,597

www.semtech.com

Share Link: