110

IN

S

out

COMP

out

V

V

C

R

L I

×

×

×

=

×

7.5

s

out

COMP

out

COMP

V

C

C

I

R

×

=

×

×

2

18

70

1.238

m

=

»

W

=

FB

FB

V

R

k

A

V

V

1

2

1

S

FB

V

R

R

V

æ

ö

=

×

-

ç

÷

è

ø

V

FB

R1

R2

V

S

D

avg

forward

P

I

V

=

×

avg

out

I

I

=

TPS61087

www.ti.com

SLVS821C – MAY 2008 – REVISED JULY 2013

Rectifier Diode Selection

To achieve high efficiency a Schottky type should be used for the rectifier diode. The reverse voltage rating

(6)

Usually a Schottky diode with 2 A maximum average rectified forward current rating is sufficient for most

applications. The Schottky rectifier can be selected with lower forward current capability depending on the output

(7)

Typically the diode should be able to dissipate around 500mW depending on the load current and forward

voltage.

Table 2. Rectifier Diode Selection

CURRENT

SUPPLIER

COMPONENT CODE

2 A

20 V

0.44 V / 2 A

Vishay Semiconductor

SL22

2 A

20 V

0.5 V / 2 A

Fairchild Semiconductor

SS22

Setting the Output Voltage

The output voltage is set by an external resistor divider. Typically, a minimum current of 50

μA flowing through

the feedback divider gives good accuracy and noise covering. A standard low side resistor of 18 k

Ω is typically

selected. The resistors are then calculated as:

(8)

Compensation (COMP)

The regulator loop can be compensated by adjusting the external components connected to the COMP pin. The

COMP pin is the output of the internal transconductance error amplifier.

See Table 3 for dedicated compensation networks giving an improved load transient response. The following

(9)

with

Minimum input voltage

Output voltage

Output capacitance

L

Inductor value, e.g. 3.3

μH or 6.8 μH

Maximum output current in the application

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