4

Date: 08/24/04

SP7650 Wide Input Voltage Range 3A, 300kHz, Buck Regulator

© Copyright 2004 Sipex Corporation

General Overview

The SP7650 is a fixed frequency, voltage mode,

synchronous PWM regulator optimized for high

efficiency. The part has been designed to be

especially attractive for high voltage applica-

tions utilizing 5V to power the controller and

2.5V to 28V for step down conversion.

The heart of the SP7650 is a wide bandwidth

transconductance amplifier designed to accom-

modate Type II and Type III compensation

schemes. A precision 0.8V reference, present on

the positive terminal of the error amplifier per-

mits the programming of the output voltage

error amplifier, COMP, compared to a 1.1V

peak-to-peak ramp is responsible for trailing

edge PWM control. This voltage ramp, and

PWM control logic are governed by the internal

oscillator that accurately sets the PWM fre-

quency to 300kHz.

THEORY OF OPERATION

The SP7650 contains two unique control fea-

tures that are very powerful in distributed appli-

cations. First, asynchronous driver control is

enabled during start up, to prohibit the low side

switch from pulling down the output until the

high side switch has attempted to turn on. Sec-

ond, a 100% duty cycle timeout ensures that the

low side switch is periodically enhanced during

extended periods at 100% duty cycle. This guar-

antees the synchronized refreshing of the BST

capacitor during very large duty ratios.

The SP7650 also contains a number of valuable

allows the user to set the exact value at which the

conversion voltage can safely begin down con-

sures that the controller itself has enough volt-

age to properly operate. Other protection fea-

PIN DESCRIPTION

#

n

i

Pe

m

a

N

n

i

Pn

o

i

t

p

i

r

c

s

e

D

3

-

1P

D

N

G

r

e

i

f

i

t

c

e

r

s

u

o

n

o

r

h

c

n

y

s

e

h

t

r

o

f

n

o

i

t

c

e

n

n

o

c

d

n

u

o

r

G

1

2

-

9

1

,

8

,

4D

N

G

e

r

a

r

e

v

i

r

d

r

e

w

o

p

r

e

w

o

l

d

n

a

C

I

e

h

t

f

o

y

r

t

i

u

c

r

i

c

l

o

r

t

n

o

c

e

h

T

.

n

i

P

d

n

u

o

r

G

)

-

(

e

h

t

o

t

s

e

c

a

r

t

d

n

u

o

r

g

r

e

h

t

o

m

o

r

f

y

l

e

t

a

r

a

p

e

s

n

r

u

t

e

R

.

n

i

p

s

i

h

t

o

t

d

e

c

n

e

r

e

f

e

r

.

t

u

o

C

f

o

l

a

n

i

m

r

e

t

5V

B

F

t

u

p

n

i

g

n

i

t

r

e

v

n

i

e

h

t

s

i

t

I

.

n

i

p

n

o

i

t

c

e

t

e

D

t

i

u

c

r

i

C

t

r

o

h

S

d

n

a

e

g

a

t

l

o

V

k

c

a

b

d

e

e

F

r

o

f

t

n

i

o

p

k

c

a

b

d

e

e

f

e

g

a

t

l

o

v

t

u

p

t

u

o

e

h

t

s

a

s

e

v

r

e

s

d

n

a

r

e

i

f

il

p

m

A

r

o

r

r

E

e

h

t

f

o

d

e

t

s

u

j

d

a

e

b

n

a

c

d

n

a

d

e

s

n

e

s

s

i

e

g

a

t

l

o

v

t

u

p

t

u

o

e

h

T

.

r

e

t

r

e

v

n

o

C

k

c

u

B

e

h

t

V

r

e

v

e

n

e

h

W

.

r

e

d

i

v

i

d

r

o

t

s

i

s

e

r

l

a

n

r

e

t

x

e

n

a

h

g

u

o

r

h

t

B

F

e

h

t

w

o

l

e

b

V

5

2

.

0

s

p

o

r

d

p

u

c

c

i

h

s

r

e

t

n

e

C

I

e

h

t

d

n

a

d

e

t

c

e

t

e

d

s

i

t

l

u

a

f

t

i

u

c

r

i

c

t

r

o

h

s

a

,

e

c

n

e

r

e

f

e

r

e

v

i

t

i

s

o

p

.

e

d

o

m

6P

M

O

C

t

u

p

n

i

g

n

i

t

r

e

v

n

i

e

h

t

o

t

d

e

t

c

e

n

n

o

c

y

ll

a

n

r

e

t

n

i

s

i

t

I

.

r

e

i

f

il

p

m

A

r

o

r

r

E

e

h

t

f

o

t

u

p

t

u

O

d

n

a

n

e

s

o

h

c

s

i

n

o

i

t

a

n

i

b

m

o

c

r

e

t

li

f

l

a

m

i

t

p

o

n

A

.

r

o

t

a

r

a

p

m

o

c

M

W

P

e

h

t

f

o

V

r

o

d

n

u

o

r

g

r

e

h

t

i

e

d

n

a

n

i

p

s

i

h

t

o

t

d

e

t

c

e

n

n

o

c

B

F

e

g

a

t

l

o

v

e

h

t

e

z

il

i

b

a

t

s

o

t

.

p

o

o

l

e

d

o

m

7N

I

V

U

V

n

e

e

w

t

e

b

r

e

d

i

v

i

d

r

o

t

s

i

s

e

r

a

t

c

e

n

n

o

C

.

e

g

a

t

l

o

v

n

i

V

r

o

f

t

u

p

n

i

O

L

V

U

N

I

d

n

a

V

U

N

I

e

g

a

t

l

o

v

g

n

i

t

a

r

e

p

o

m

u

m

i

n

i

m

t

e

s

o

t

9S

S

e

h

t

t

e

s

o

t

D

N

G

d

n

a

S

S

n

e

e

w

t

e

b

r

o

t

i

c

a

p

a

c

l

a

n

r

e

t

x

e

n

a

t

c

e

n

n

o

C

.

t

r

a

t

S

t

f

o

S

w

o

l

d

l

e

h

s

i

n

i

p

S

S

e

h

T

.

t

n

e

r

r

u

c

e

c

r

u

o

s

A

µ

0

1

e

h

t

n

o

d

e

s

a

b

e

t

a

r

t

r

a

t

s

t

f

o

s

.

s

n

o

i

t

i

d

n

o

c

t

l

u

a

f

ll

a

g

n

i

r

u

d

t

n

e

r

r

u

c

)

n

i

m

(

A

m

1

a

a

i

v

3

1

-

0

1V

N

I

g

n

il

p

u

o

c

e

d

a

e

c

a

l

P

.

T

E

F

S

O

M

l

e

n

n

a

h

c

-

N

e

d

i

s

h

g

i

h

e

h

t

o

t

n

o

i

t

c

e

n

n

o

c

t

u

p

n

I

.

D

N

G

P

d

n

a

n

i

p

s

i

h

t

n

e

e

w

t

e

b

r

o

t

i

c

a

p

a

c

6

2

-

3

2

,

6

1

-

4

1X

LV

d

n

a

n

i

p

s

i

h

t

n

e

e

w

t

e

b

r

o

t

c

u

d

n

i

n

a

t

c

e

n

n

o

C

T

U

O

2

2V

C

C

y

l

p

p

u

s

s

a

i

b

V

5

l

a

n

r

e

t

x

e

r

o

f

t

u

p

n

I

7

1C

Nt

c

e

n

n

o

C

o

N