SM6702 series
PFM Step-up DC/DC Converter
OVERVIEW
The SM6702 series are step-up DC/DC converter ICs, fabricated using NPC’s Molybdenum-gate CMOS pro-
cess. They incorporate reference voltage source, error amplifier, oscillator, start-up circuit, PFM (Pulse Fre-
quency Modulation) control circuit into a single chip. The only external components required are a Coil, Diode
and output smoothing capacitors to form a step-up DC/DC converter. They employ PFM voltage control cir-
cuits to achieve high efficiency, stable constant-voltage output.
FEATURES
I
PINOUT
(Top view)
I
I
I
I
I
Power dissipation: 24µW at V
IN
= 1.5V, V
OUT
=
3.0V, I
OUT
= 100µA
Start-up input voltage: 0.9V (max) at R
L
= 30kΩ
Output voltage: 2.2 to 3.3V, available in 0.1Vstep
High efficiency: 85% at V
IN
= 1.5V, V
OUT
= 3.0V,
I
OUT
= 1mA
Low ripple voltage
Package: SOT89-3
APPLICATIONS
I
I
I
I
I
PDA, Mobile IT equipment
Digital Still Camera
Pager
Constant-voltage sources for battery-operated
equipment
Local voltage sources
1
VSS
2
OUT
3
LX
PACKAGE DIMENSIONS
(Unit: mm)
ORDERING INFORMATION
Device
SM6702-33HB
SM6702-30HB
SM6702-27HB
Output voltage
1
3.3V
3.0V
2.7V
Package
SOT89-3
4.5
±
0.1
1.55
±
0.15
(0.4)
(5 )
4.0
±
0.3
0.1
±
0.05
(8 )
0.42
±
0.1
0.47
±
0.1
(5 )
1.5
±
0.1
0.4
±
0.1
SOT89-3
SOT89-3
1. Stepwise setting with a step of 0.1V in the range of 2.2V to 3.3V is
available.
1.1
±
0.2
2.5
±
0.1
φ
1
.0
1.5
1.5
0.37
±
0.1
(8 )
0.42
±
0.1
NIPPON PRECISION CIRCUITS INC.—1
SM6702 series
BLOCK DIAGRAM
OUT
LX
PFM OSC
VREF
START−UP
VSS
PIN DESCRIPTION
Number
1
2
3
Name
VSS
OUT
LX
Ground
Output (device supply pin)
Switching pin
Description
NIPPON PRECISION CIRCUITS INC.—2
SM6702 series
SPECIFICATIONS
Absolute Maximum Ratings
T
a
= 25°C
Parameter
LX impressed voltage
OUT impressed voltage
LX output current
Power dissipation
Operating temperature
Storage temperature
Symbol
V
LX
V
OUT
I
LX
P
D
T
opr
T
stg
Condition
Rating
5
4
200
500
−
20 to 70
−
40 to 125
Unit
V
V
mA
mW
°C
°C
Electrical Characteristics
L = 330µH, C = 22µF, T
a
= 25°C, V
SS
= 0V
Rating
Parameter
Start-up voltage
Holding voltage
Current consumption
Output voltage
Symbol
V
st
V
hold
I
SS
V
OUT
I
LX
I
LXL
f
OSC
Duty
V
IN
R
L
= 30kΩ
R
L
= 3kΩ
V
IN
= 1.5V, R
L
= 30kΩ
V
IN
= 1.5V, R
L
= 3kΩ
V
OUT
= V
target
−
0.1,
V
LX
= 0.4V
V
OUT
= V
LX
= 3.5V
V
OUT
= V
target
−
0.1
V
OUT
= V
target
−
0.1
2.2
≤
V
target
≤
2.7
2.8
≤
V
target
≤
3.3
Condition
min
–
–
–
V
target
×
0.975
60
80
–
80
65
–
typ
–
–
8
V
target
–
–
–
100
75
–
max
0.9
0.7
16
V
target
×
1.025
–
mA
–
1
120
85
V
target
+
0.2
µA
kHz
%
V
V
V
µA
V
Unit
LX output current
LX leakage current
Maximum oscillator frequency
Switch ON duty cycle
Input voltage range
V
target
: Setting output voltage
NIPPON PRECISION CIRCUITS INC.—3
SM6702 series
FUNCTIONAL DESCRIPTION
Step-up Principle
The SM6702 series use a transistor to switch the input supply in a non-isolated chopper switching regulator
configuration. The figure below shows the basic step-up switching regulator circuit.
If the transistor is ON for an interval t
ON
and then instantly turned OFF, the energy stored in the coil L during
the interval t
ON
generates a voltage V
L
across the coil. This voltage is superimposed on the input voltage such
that the peak voltage reaches V
IN
+ V
L
which forces the diode D to conduct and release the stored energy into
the output.
During normal operation, the above switching occurs repeatedly at a frequency controlled by an oscillator
(which can change depending on the input and output load conditions), generating a square wave output which
is then smoothed by the output capacitor C. Thus the output voltage (V
OUT
> V
IN
) has been stepped up.
L
V
IN
D
V
OUT
Tr
C
GND
PFM Control
In SM6702 series, the LX transistor ON interval is fixed, and the OFF interval varies in response to the input
voltage and load changes. Thus the resulting switching cycle frequency varies, called pulse frequency modula-
tion.
NIPPON PRECISION CIRCUITS INC.—4
SM6702 series
BASIC CIRCUIT
L
V
IN
D
OUT
+
C
LX
VSS
OUT
Coil (L) : 330µH
Diode (D) : MA721 (Matsushita Schottky diode)
Capacitor (C
L
) : 22µF tantalum
TYPICAL APPLICATION CIRCUIT
L
D
3V System
Voltage
+
LX
C2
VSS
OUT
+
1.5V
C1
C3
Coil (L) : 330µH
Schottky Diode (D)
Capacitor (C1) : 22µF tantalum
Capacitor (C2) : 0.22µF ceramic
Capacitor (C3) : 22µF tantalum
NIPPON PRECISION CIRCUITS INC.—5
51单片机
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