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SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator General Description
The SM8303 is a monolithic integrated circuit that provide all the active functions for a step-down switching regulator, capable of driving a 3A 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 SM8303 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 5-lead TO-220(T) package and a 5-lead TO-263(S).
SM8303
Features
- 3.3V, 5V, 12V and adjustable output versions - Adjustable version output voltage range, 1.23V to 28V +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 32V - Output load current: 3A - 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 VIN
Pin Descriptions
Name VIN Output Gnd FB Description Operating voltage input Switching output Ground Output voltage feedback control ON/OFF Shutdown
Metal Tab GND
TO263-5L ( Top View ) 5 SD 4 FB 3 Gnd 2 Output 1 VIN TO220-5L
SD
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V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Ordering Information
SM8303
SM8303 XX X X
Output version -ADJ : Adjustable -33 : 3.3V -50 : 5.0V -12 : 12V Package T: TO220-5L S: TO263-5L Packing Blank : Tube A : Taping
Block Diagram
SD
VIN
200mV Current Source bias 1.235V Reference 2.5V Regulator Start up 220mV
+ Comp _
Comp +
+
FB
_
Comp +
_
Amp
Pre-driver
150kHz OSC.
Thermal Limit
2
_
3A Switch
Output Gnd
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Absolute Maximum Ratings
Symbol VCC VSD VFB VOUT PD TST TOP VOP Parameter Supply Voltage ON/OFF Pin input voltage Feedback Pin voltage Output voltage to Ground Power dissipation Storage temperature Operating temperature Operating voltage Rating +35 -0.3 to +25 -0.3 to +25 -1 Internally limited -65 to +150 -40 to +125 +4.5 to +25
SM8303
Unit V V V V W
o o
C C
V
Electrical Characteristics (All Output Voltage Versions)
Unless otherwise specified, VIN=12V for 3.3V, 5V, adjustable version and VIN=24V for the 12V version. ILOAD = 0.3A
Symbol IB FOSC VSAT DC ICL
Parameter Feedback bias current oscillator frequency 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
Conditions VFB=1.3V (Adjustable version only)
Min.
Typ. 40
Max. 60 100 173 173 1.4 1.5
Unit nA Khz V %
127 110 IOUT=3A no outside circuit VFB=0V force driver on VFB=0V force driver on VFB=12V force driver off peak current no outside circuit VFB=0 force driver on no outside circuit VFB=12 force driver off VIN=32V VFB=12 force driver off ON/OFF pin=5V VIN=24V Low (regulator ON) High (regulator OFF) 2.0
150
1.3 100 0 3.6 4.5
5.5 6.5 200
A uA mA mA uA
IL IQ ISTBY VIL VIH IH IL JC JA
2 5 150
60 10 250 300 0.6
1.3 15 0.02 2.5 3.5 28 23
25 5
o
V
ON/OFF pin logic VLOGIC=2.5V (OFF) input current ON/OFF pin input current VLOGIC=0.5V (ON) Thermal Resistance Thermal Resistance With copper area of approximately 3 in2 TO220-5L TO263-5L TO220-5L TO263-5L Junction to case Junction to ambient 3
uA C/W C/W
o
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Electrical Characteristics (Continued)
Symbol
VFB
SM8303
Parameter Output Feedback Efficiency Output voltage Efficiency Output voltage Efficiency Output voltage Efficiency
Conditions 5V < VIN < 32V 0.2A < ILOAD < 3A VOUT programmed for 3V VIN = 12V, ILOAD=3A 5.5V < VIN < 32V 0.2A < ILOAD < 3A VIN = 12V, ILOAD=3A 8V < VIN < 32V 0.2A < ILOAD < 3A VIN = 12V, ILOAD=3A 15V < VIN < 32V 0.2A < ILOAD < 3A VIN = 15V, ILOAD = 3A
Typ. 1.23 73 3.3 73 5 80 12 90
Limit 1.193/1.18 1.267/1.28
Unit V VMIN VMAX %
SM8303-ADJ
VOUT VOUT VOUT
SM8303-3.3V
3.168/3.135 3.432/3.465
V VMIN VMAX % V VMIN VMAX % V VMIN VMAX %
SM8303-5V
4.8/4.75 5.2/5.25
SM8303-12V
11.52/11.4 12.48/12.6
Specifications with boldface type are for full operating temperature range, the other type are for TJ=25C.
4
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Typical Performance Characteristics
Typical Performance Characteristics Normalized Output Voltage
5.10
OUTPUT VOLTAGE CHANGE
VIN =20V, I LOAD=3A Normalized at TJ=25oC
SM8303
Efficiency
100
EFFICIENCY (%)
5.05
95 90 85 80 75
3A 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(oC)
JUNCTION TEMPERATURE(oC)
Switch Saturation Voltage
1.7
SATURATION VOLTAGE (V)
Switch Current Limit
8.0
Output voltage Vo(V)
1.6 1.5 1.4
1 : -40 oC 2 : 25 oC 3 : 125 oC
6.0
VIN
=10V 20V 40V
4.0
1 1.3 1.2 3 2.0 3 4 5 2
2.0
0.0 0 1 2 3 4 5 6 7
SWITCH CURRENT(A) Output current Io (A)
Operating Quiescent Current
25.0
SUPPLY CURRENT (mA)
Shutdown Quiescent Current
200.0 130.0
CURRENT (uA)
20.0 15.0 10.0 5.0 0.0 -50 -25 0 25 50 75 100 125
Switch ON Switch OFF
100.0 80.0 40.0 0.0
1 2 3
VON/OFF=5V 1 : -40 oC 2 : 25 oC 3 : 125 oC
20 30 40
10
JUNCTION TEMPERATURE(oC)
SUPPLY VOLOTAGE (V)
5
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SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Typical Performance Characteristics (Continued)
Minimum Operating Supply Voltage
5.0 4.0
SUPPLY VOLTAGE (V) THRESHOLD VOLTAGE (V)
SM8303
ON /OFF Threshold Voltage
5.0 4.0 3.0 2.0 1.0 0.0
3.0 2.0 1.0 0.0 -50 -25 0 25 50 75 100 125
JUNCTION TEMPERATURE ( oC)
V OUT =1.23V I LOAD =120mA
-50 -25
0
25
50
75 100
125
JUNCTION TEMPERATURE ( oC)
ON/OFF Pin Current (Sinking )
150.0 120.0
CURRENT (uA)
Switch Frequency
68.0
90.0 60.0 30.0 0.0
FREQUENCY (kHz)
VIN =40V -40o C Tj 125 o C
51.0 34.0 17.0 0.0
1.4
5
10
15
20 22
23
24
25
-50 -25
0
25
50
75
100
o
125
ON/OFF PIN VOLTAGE (V)
JUNCTION TEMPERATURE ( C)
Feedback Pin Bias Current
50.0
BIAS CURRENT (nA)
Thermal protection
10
Output voltage Vo(V)
40.0 30.0 20.0 10.0 0.0 -50 -25 0 25 50 75 100 125
8 6 4 2
TSC OFF TSD ON
Adjustable Version Only
0
JUNCTION TEMPERATURE ( oC)
50
75
100
125
150
175
200
JUNCTION TEMPERATURE ( o C)
6
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Typical Application Circuit
A Fixed Type Circuit
SM8303
FB
12V
DC Input Vin 1 5
4
SM8303
3 SD
2
Output
L1
Inductor
3.3V/3A
Output Load
Cin
Capacitor
Gnd
D1
Schottky Diode
Co
Capacitor
(B) Adjustable Type Circuit
R2
FB
R1
12V
DC Input Vin 1 5
4
SM8303
3 SD
2
Output
L1
68uF
3.3V/3A
Output Load
Cin 680uF
Gnd
D1 1N5824
Co 1000 uF
Vout = VFB x (1+ R1/R2 )
VFB=1.23V
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V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Function Description
Pin Functions +VIN This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. Output Internal switch and power output. The voltage at this pin switches between (+VIN - VSAT) and approximately - 0.5V, with a duty cycle of approximately VOUT / VIN. The PC board copper area connected to this pin should be kept a minimum in order to reduce the coupling sensitivity to the circuitry Ground Circuit ground. Feedback Complete the feedback loop by sensing the regulated output voltage
ON /OFF Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 100uA. Pulling this pin below a threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin above 1.3V (up to a maximum of 25V) shuts the regulator down. If this shutdown
SM8303
all approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require more heat sinking. The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. The copper and the board are the heat sink for this package and the other heat producing components, such as the catch diode and inductor. The PC board copper area that the package is soldered to should be at least 0.8 in2, and ideally should have 2 or more square inches of 2 oz. Additional copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in2, only small improvements in heat dissipation are realized. If further thermal improvements are needed, double sided, multilayer PC board with large copper areas and/or airflow are recommended.
Function Description (Continued)
The SM8303 (TO-263 package) junction temperature rise above ambient temperature with a 2A load for various input and output voltages. This data was taken with the circuit operating as a buck switching regulator with all components mounted on a PC board to simulate the junction temperature under actual operating conditions. This curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware that there are many factors that can affect the junction temperature. When load currents higher than 3A are used, double sided or multilayer PC boards with large copper areas and/or airflow might be needed, especially for high ambient temperatures and high output voltages. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (Once exception to this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding
feature is not needed, the ON /OFF pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the ON condition. Thermal Considerations The SM8303 is available in two packages, a 5-pin TO-220 and a 5-pin surface mount TO-263. The TO-220 package needs a heat sink under most conditions. The size of the heatsink depends on the input voltage, the output voltage, the load current and the ambient temperature. The SM8303 junction temperature rises above ambient temperature for a 3A load and different input and output voltages. The data for these curves was taken with the SM8303 (TO-220 package) operating as a buck switching regulator in an ambient temperature of 25oC (still air). These temperature rise numbers are 8
air, and moving air lowers the thermal resistance even further. Package thermal resistance and junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers. Some of these factors include board V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator
size, shape, thickness, position, location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper thickness, single or double-sided, multilayer board and the amount of solder on the board. The effectiveness of the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surrounding
SM8303
air is still or moving. Furthermore, some of these components such as the catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the inductor, depending on the physical size, type of core material and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board.
Marking Information
(1) TO263-5L
( Top view )
(2) TO220-5L
( Top view )
Output Type : 8303-ADJ: ADJ 8303-33: 3.3V 8303-50: 5.0V 8303-12: 12V
SM 8303XX YY WW ~
Logo ID code Xth week : 01~52 Year: "03" = 2003 "04" = 2004
Output Type : 8303-ADJ: ADJ 8303-33: 3.3V 8303-50: 5.0V 8303-12: 12V
SM 8303-XX YY WW ~
Logo ID code Xth week : 01~52 Year: "03" = 2003 "04" = 2004
~
~
9
V1.0 May 17 ,2007
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Package Information
(1) Package Type: TO220-5L
SM8303
E oP H1 Q
A
F
D
e1
L
e
b
C J1
Symbol A b C D E e e1 F H1 J1 L oP Q
Dimensions In Millimeters Min. 3.56 0.38 0.36 14.22 9.65 1.702 BSC 6.858 0.508 5.84 2.03 12.70 3.53 2.54 8.89 1.397 6.86 2.92 14.73 4.10 3.43 10 Max. 4.83 1.02 0.61 16.51 10.67
Dimensions In Inches Min. 0.140 0.015 0.014 0.560 0.380 0.067 BSC 0.270 0.020 0.230 0.080 0.520 0.139 0.100 0.350 0.055 0.270 0.115 0.580 0.161 0.135 V1.0 May 17 ,2007 Max. 0.190 0.040 0.024 0.650 0.420
SAMHOP Microelectronics Corp. 150KHz, 3A PWM Buck Switching Regulator Package Information (Continued)
(2) Package Type: TO263-5L
E F
SM8303
L1
A
C2
D L
e
B
C
Symbol A B C C2 D E e F L L1
Dimensions In Millimeters Min. 4.064 0.508 0.381 1.143 8.382 9.652 1.702 BSC 6.223 14.605 15.875 1.676 11 Max. 4.826 0.991 0.737 1.651 9.652 10.668
Dimensions In Inches Min. 0.160 0.020 0.015 0.045 0.330 0.380 0.067 BSC 0.245 0.575 0.625 0.066 V1.0 May 17 ,2007 Max. 0.190 0.039 0.029 0.065 0.380 0.420

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