Revision 1, December 2002 www.gammamicro.com
FIXED FREQUENCY STEP-UP DC/DC CONVERTER
GM7620
PRELIMINARY
1
The GM7620 is a fixed frequency step-up DC/DC
converter designed to operate as a constant-current
source. Because it directly regulates output current,
the GM7620 is ideal for driving light emitting diodes
(LEDs) whose light intensity is proportional to the
current passing through them, not the voltage across
their terminals.
With an input voltage range of 1V to 10V, the device
works from a variety of input sources. The GM7620
accurately regulates LED current even when the input
voltage is higher than the LED voltage, greatly
simplifying batterypowered designs. A single external
resistor sets LED current between 5mA and 40mA,
which can then be easily adjusted using either a DC
voltage or a pulse width modulated (PWM) signal.
When the GM7620 is placed in shutdown, the LEDs
are disconnected from the output, ensuring a quiescent
current of under 1mA for the entire circuit. The device's
1.2MHz switching frequency permits the use of tiny,
low profile chip inductors and capacitors to minimize
footprint and cost in space-conscious portable
applications.
The GM7620 is available in 6-lead plastic SOT-23
package.
Handheld Computers
Cellular Telephones
Digital Cameras
Portable MP3 Players
Applications:
1.2MHz Fixed Frequency Switching
Inherently Matched LED Current
Adjustable Control of LED Current
Drives Five White LEDs from 2V
Drives Six White LEDs from 2.7V
Drives Eight White LEDs from 3V
Disconnects LEDs In Shutdown
Uses Tiny Ceramic Capacitors
Uses Tiny 1mm-Tall Inductors
Regulates Current Even When V
IN
> V
OUT
Operates with V
IN
as Low as 1V
Up to 80% Efficiency
TYPICAL APPLICATION (Li-ION Driver for 4 White LEDs)
SW
GND
LED
R
SET
V
IN
SHDN
1
2
3
4
6
5
R
SET
1.5k
C2
1
F
C1
4.7
F
L1
6.8
H
V
IN
PWM
DIMMING
CONTROL
2.7V to 4.2V
15mA
D1
GM7620
Revision 1, December 2002 www.gammamicro.com
FIXED FREQUENCY STEP-UP DC/DC CONVERTER
GM7620
PRELIMINARY
2
PIN CONNECTIONS
SW 1
GND 2
LED 3
4 R
SET
6 V
IN
5 SHDN
6-lead SOT-23
(Top View)
N
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P
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M
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PIN CONNECTIONS AND FUNCTIONS
.
0
2
6
7
M
G
E
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C
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M
G
ORDERING INFORMATION
Revision 1, December 2002 www.gammamicro.com
FIXED FREQUENCY STEP-UP DC/DC CONVERTER
GM7620
PRELIMINARY
3
ELECTRICAL CHARACTERISTICS
(V
IN
= 1.2V, V
SHDN
= 1.2V
,
unless otherwise specified)
R
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T
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M
A
R
A
P
S
N
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V
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V
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.
0
=
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=
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1
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1
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k
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1
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6
5
=
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,
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V
5
.
1
=
R
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S
0
5
7
=
V
,
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I
V
2
.
1
=
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S
V
,
k
0
5
.
1
=
N
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V
2
.
1
=
R
T
E
S
V
,
k
3
5
.
4
=
N
I
V
2
.
1
=
3
3
5
2
5
.
2
1
8
3
0
3
5
1
5
5
4
6
3
5
.
7
1
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5
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5
9
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S
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0
5
5
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A
m
V
h
c
ti
w
S
T
A
S
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I
W
S
A
m
0
0
3
=
0
5
1
0
0
2
V
m
t
n
e
r
r
u
C
n
i
P
N
D
H
S
V
N
D
H
S
V
0
=
V
N
D
H
S
V
2
=
0
5
1
1
.
0
0
3
A
)
n
i
P
N
D
H
S
(
d
l
o
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T
p
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d
l
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S
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.
0
5
2
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t
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f
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w
S
W
S
V
5
=
1
0
.
0
5
A
* specification that apply over the full operating temperature range (The GM7620 is guaranteed to meet specifications from
0C to 70C. Specifications over the 40C to 85C operating temperature range are assured by design, characterization
and correlation with statistical process controls), otherwise specifications are T
A
= 25C.
Revision 1, December 2002 www.gammamicro.com
FIXED FREQUENCY STEP-UP DC/DC CONVERTER
GM7620
PRELIMINARY
4
G
N
I
T
A
R
E
U
L
A
V
T
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N
U
V
N
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1
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1
V
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6
3
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V
(
e
g
a
tl
o
V
D
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L
1
n
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P
)
V
0
4
=
6
3
V
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g
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V
1
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r
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2
1
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t
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)
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c
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s
0
1
,
g
n
ir
e
d
l
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s
(
e
r
u
t
a
r
e
p
m
e
T
d
a
e
L
0
0
3
+
C
ABSOLUTE MAXIMUM RATINGS
SW
GND
LED
R
SET
R
SET
C2
L1
V
IN
D1
I
SET
I
LED
V
OUT
1
2
3
4
5
6
SHDN
V
IN
C1
LED CURRENT
REFERENCE
+
-
A1
+
-
A2
DRIVER
+
-
DRIVER
Q1
0.04
+
+
1.2MHz Oscillator
Q
S
R
x5
Q2
BLOCK DIAGRAM
Revision 1, December 2002 www.gammamicro.com
FIXED FREQUENCY STEP-UP DC/DC CONVERTER
GM7620
PRELIMINARY
5
SOT-23-6 PACKAGE OUTLINE DIMENSIONS
NOTES:
1. PACKAGE BODY SIZES EXCLUDE
MOLD FLASH AND GATE BURRS
2. DIMENSION L IS MEASURED IN
GAGE PLANE
3. TOLERANCE 0.10 mm
UNLESS OTHERWISE SPECIFIED
4. COPLANARITY: 0.10 mm
L
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.
1
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1
.
1
0
3
.
1
1
A
0
-
0
1
.
0
2
A
0
7
.
0
0
8
.
0
0
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.
0
b
5
3
.
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0
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.
0
0
5
.
0
C
0
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