SAMHOP Microelectronics Corp.
150KHz, 2A PWM Buck Switching Regulator
General Description
The SM8312 is a monolithic integrated circuit that
provide all the active functions for a step-down
switching regulator, capable of driving a 2A load
without additional transistor component. Requiring
a minimum number of external component, the
board space can be saved easily. The external
shutdown function can be controlled by TTL logic
level and then come into standby mode. The
internal compensation makes feedback control
have good line and load regulation without external
design. Regarding protected function, thermal
shutdown is to prevent over temperature operating
from damage, and current limit is against over
current operating of the output switch. The SM8312
operates at a switching frequency of 150KHz thus
allowing smaller sized filter components than what
would be needed with lower frequency switching
regulators. Other features include a guaranteed
+4% tolerance on output voltage under specified
input voltage and output load conditions, and +15%
on the oscillator frequency. The output version
included fixed 3.3V, 5V, 12V, and an adjustable
type. The packages are available in a standard
8-lead SOP8 package and a 5-lead TO-263(U).
SM8312
Features
-
3.3V, 5V, 12V and adjustable output versions
-
Adjustable version output voltage range, 1.23V to
37V +4% max over line and load condition
-
Available in TO220-5L and TO263-5L packages
-
Voltage mode non-synchronous PWM control
-
Thermal-shutdown and current-limit protection
-
ON/OFF shutdown control input
-
Input voltage range up to 40V
-
Output load current: 2A
-
150KHz fixed frequency internal oscillator
-
Low power standby mode
-
Built-in switching transistor on chip
Applications
-
Simple High-efficiency step-down(buck) regulator
-
Efficient preregulator for linear regulators
-
On-card switching regulators
-
Positive to negative converter
- Battery Charger
Pin Assignments
( Top View )
5 SD
4 FB
3 Gnd
2 Output
1 V
IN
Metal Tab GND
Pin Descriptions
Name
Description
V
IN
Output
Gnd
FB
Operating voltage input
Switching output
Ground
Output voltage feedback control
ON/OFF Shutdown
TO263-5L
V
IN
OUT
FB
SD
1
2
3
4
8
7
6
5
GND
GND
GND
GND
SD
SOP-8
1
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp.
150KHz, 2A PWM Buck Switching Regulator
Absolute Maximum Ratings
Symbol
Parameter
Rating
SM8312
Unit
V
CC
V
SD
V
FB
V
OUT
P
D
T
ST
T
OP
V
OP
Supply Voltage
ON/OFF Pin input voltage
Feedback Pin voltage
Output voltage to Ground
Power dissipation
Storage temperature
Operating temperature
Operating voltage
+45
-0.3 to +25
-0.3 to +25
-1
Internally limited
-65 to +150
-40 to +125
+4.5 to +25
V
V
V
V
W
o
o
C
C
V
Electrical Characteristics (All Output Voltage Versions)
Unless otherwise specified, V
IN
=12V for 3.3V, 5V, adjustable version and V
IN
=24V for the 12V version. I
LOAD
= 0.2A
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
I
B
F
OSC
Fscp
V
SAT
DC
I
CL
Feedback bias current
oscillator frequency
Oscillator frequency
short circuit protect
saturation voltage
Max. Duty Cycle(ON)
Min. Duty cycle(OFF)
current limit
Output = 0V Output
leakage
Output= -1V current
Quiescent Current
Standby Quiescent
Current
ON/OFF pin logic input
threshold voltage
V
FB
=1.3V
(Adjustable version only)
127
110
-10
150
30
1.25
100
0
2.4
2.8
-50
-100
173
173
nA
Khz
Khz
V
%
of When current limit occurred
and V
FB
<0.55V
I
OUT
=2A
no outside circuit
V
FB
=0V force driver on
V
FB
=0V force driver on
V
FB
=12V force driver off
peak current
no outside circuit
V
FB
=0 force driver on
no outside circuit
V
FB
=12 force driver off
V
IN
=24V
V
FB
=12 force driver off
ON/OFF pin=5V
V
IN
=24V
Low (regulator ON)
High (regulator OFF)
-
2.0
70
1.4
1.5
3.3
3.6
-200
A
uA
mA
mA
uA
I
L
I
Q
I
STBY
V
IL
V
IH
I
H
I
L
Ts
-5
5
70
-30
10
150
200
0.6
1.3
-
-0.01
-0.1
175
150
-1
o
V
ON/OFF pin logic
V
LOGIC
=2.5V (OFF)
input current
ON/OFF pin input current V
LOGIC
=0.5V (ON)
Over temperature
shutdown threshold
Tj increasing
Tj decreasing
uA
C
3
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp.
150KHz, 2A PWM Buck Switching Regulator
Typical Performance Characteristics
Typical Performance Characteristics
Normalized Output Voltage
5.10
OUTPUT VOLTAGE CHANGE
V
IN
=20V, I
LOAD
=2A
Normalized at T
J
=25
o
C
SM8312
Efficiency
100
EFFICIENCY (%)
5.05
95
90
85
80
75
2A Load
5.00
5V
4.95
3.3V
4.90
-50
-25
0
25
50
75
100
125
70
8
10
15
20
25
30
35
40
JUNCTION TEMPERATURE(
o
C)
JUNCTION TEMPERATURE(
o
C)
Switch Saturation Voltage
1.7
SATURATION VOLTAGE (V)
Switch Current Limit
6.5
SWITCH CURRENT LIMIT (A)
1.6
1.5
1.4
1 : -40
2 : 25
o
C
3 : 125
o
C
o
C
V
IN
=12V, V
OUT
=5V
6.0
5.5
1
1.3
1.2
3
2.0
3
4
5
2
5.0
4.5
-50
-25
0
25
50
75
100 125
SWITCH CURRENT(A)
JUNCTION
TEMPERATURE(
o
C)
Operating Quiescent Current
25.0
SUPPLY CURRENT (mA)
Shutdown Quiescent Current
200.0
160.0
CURRENT (uA)
20.0
15.0
10.0
5.0
0.0
-50
-25
0
25
50
75
100
125
Switch ON
Switch OFF
120.0
80.0
40.0
0.0
1
2
3
V
ON/OFF
=5V
1 : -40
o
C
2 : 25
o
C
3 : 125
o
C
20
30
40
10
JUNCTION TEMPERATURE(
o
C)
SUPPLY VOLOTAGE (V)
5
V1.0 May 17 ,2007
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