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SS6638G
Simple 3-Pin Step-Up DC/DC Converter
FEATURES
Guaranteed start-up from less than 0.9 V. High efficiency. Low quiescent current. Fewer external components needed. Low ripple and low noise. Fixed output voltage: 2.7V, 3.0V, 3.3V, 4.5V and 5V. Space saving packages: SOT-23, SOT-89 and TO-92.
DESCRIPTION
The SS6638G is a high-efficiency step-up DC/DC converter for applications using 1 to 4 NiMH battery cells. Only three external components are required to deliver a fixed output voltage of 2.7V, 3.0V, 3.3V, 4.5V or 5V. The SS6638G starts up from less than 0.9V input with 1mA load. A Pulse Frequency Modulation scheme brings optimized performance for applications with light output loading and low input voltages. The output ripple and noise are lower compared with circuits operating in PSM mode. The PFM control circuit operating at a maximum 100kHz switching rate results in smaller passive components. The space saving SOT-23, SOT-89 and TO-92 packages make the SS6638G an ideal choice of DC/DC converter for space-conscious applications, like pagers, electronic cameras, and wireless microphones.
Pb-free, RoHS compliant.
APPLICATIONS
Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Supplies. Portable Instruments.
TYPICAL APPLICATION CIRCUIT
VIN L1 100H D1 SS12 SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G GND VOUT
+
C1 SW 22F
VOUT
+ C2 47F
Simple Step-Up DC/DC Converter
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SS6638G
ORDERING INFORMATION
SS6638-XX X X XX
Packing TR: Tape and reel Package type X: SOT-89 Z: TO-92 U: SOT-23 G: Pb-free, RoHS-compliant Output voltage 27: 2.7V 30: 3.0V 33: 3.3V 45: 4.5V 50: 5.0V Example: SS6638-27GXTR 2.7V output in RoHS-compliant SOT-89, shipped on tape and reel
PIN CONFIGURATION
SOT-89 TOP VIEW 1: GND 2: VOUT 3: SW
1 2 3
TO-92 TOP VIEW 1: GND 2: VOUT 3: SW
1 2 3
SOT-23 TOP VIEW 1: GND 2: VOUT 3: SW 1
2
3
SOT-23 MARKING Part No.
SS6638-27GU
SS6638-30GU
SS6638-33GU
SS6638-45GU
SS6638-50GU
SOT-89 MARKING Part No.
SS6638-27GX
SS6638-30GX
SS6638-33GX
SS6638-45GX
SS6638-50GX
DA27P
DA30P
DA33P
DA45P
DA50P
AN27P
AN30P
AN33P
AN45P
AN50P
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SS6638G
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VOUT pin) SW pin Voltage SW pin Switch Current Operating Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering 10 Sec.) .6V 6V 0.6A -40C to 85C 125C -65C to 150 C 260C
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
TEST CIRCUIT
IIN VIN D1 SS12 SS6638-27G SS6638-30G SS6638-33G SS6638-45G VOUT SS6638-50G GND VOUT
L1 100H
+
C1 SW 22F
+ C2 47F
Fig. 1 Test Circuit 1
IS
SS6638G VOUT GND SW VSW VS
SS6638G 100 VOUT GND SW FOSC
VS
Fig. 2 Test Circuit 2
Fig. 3 Test Circuit 3
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SS6638G
ELECTRICAL CHARACTERISTICS
PARAMETER TEST CONDITIONS
SS6638-27G SS6638-30G Output Voltage SS6638-33G SS6638-45G SS6638-50G Input Voltage Start-Up Voltage Min. Hold-on Voltage No-Load Input Current VIN=1.8V VIN=1.8V VIN=2.0V VIN=3.0V VIN=3.0V 1 1 1 1 VIN VSTART VHOLD IIN 15 42 50 60 2 IS1 70 90 A 0.8 1 VOUT
(TA=25C, IOUT=10mA, unless otherwise specified) (Note1)
TEST CKT SYMBOL
MIN.
2.633 2.925 3.218 4.387 4.875
TYP.
2.700 3.000 3.300 4.500 5.000
MAX.
2.767 3.075 3.382 4.613 5.125 6 0.9 0.7
UNIT
V
Normal Operation IOUT=1mA, VIN:02V IOUT=1mA, VIN:20V IOUT=0mA SS6638-27G SS6638-30G SS6638-33G
V V V A
Supply Current
SS6638-45G SS6638-50G VS=VOUT x 0.95 Measurement of the IC input current (VOUT pin) SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G VS=VOUT + 0.5V Measurement of the IC input current (VOUT pin)
7 7 7 2 IS2 7 7 A
Supply Current
SW Leakage Current
VSW=6V, VS=VOUT + 0.5V SS6638-27G SS6638-30G SS6638-33G
2 1.3 1.2 1.1 2 RON 1 1
0.5
A
SW Switch-On Resistance
SS6638-45G SS6638-50G VS=VOUT x 0.95, VSW=0.4V
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SS6638G
ELECTRICAL CHARACTERISTICS
PARAMETER
(Continued)
TEST CKT
TEST CONDITIONS
VS=VOUT x 0.95
SYMBOL
MIN.
TYP.
MAX.
UNIT
Oscillator Duty Cycle
Measurement of the SW pin waveform VS=VOUT x 0.95
3
DUTY
65
75
85
%
Max. Oscillator Freq. Efficiency
Measurement of the SW pin waveform
3 1
FOSC
80
105 85
130
kHz %
Note 1: Specifications are production tested at TA=25C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC).
TYPICAL PERFORMANCE CHARACTERISTICS (Refer to Typical Application)
Capacitor (C2) : 47F (Tantalum Type) Diode (D1) : 1N5819 Schottky Type
2.8
85 80
2.7
Output Voltage (V)
VIN =1.5V
VIN =2.0V
V IN =1.2V
2.5
Efficiency (%)
2.6
VIN =1.8V
75
70
VIN=1.8V
VIN=2.0V
2.4
65
V IN =0.9V
2.3
60
VIN=1.5V
VIN=0.9V
2.2 0
55
VIN=1.2V
40 60 80 100 120 140 160 180
20
40
60
80
100
120
140
160
180
0
20
Output Current (mA) Fig. 4 SS6638-27G Load Regulation (L=100H CD54)
Output current (mA) Fig. 5 SS6638-27G Efficiency (L=100H CD54)
2.8
85 80
2.7
75
Output Voltage (V)
2.6
Efficiency (%)
VIN=1.2V
2.5
VIN=1.5V
VIN=1.8V
VIN=2.0V
70
VIN=2.0V
65 60
VIN=1.8V
2.4
VIN=1.2V
55
VIN=1.5V
VIN=0.9V
VIN=0.9V
2.3 0 20 40 60 80 100 120 140 160 180 200 220 240
50
0
20
40
60
80
100
120
140
160
180
200
220 240
Output Current (mA)
Fig. 6
SS6638-27G Load Regulation (L=47H CD54)
Output current (mA) Fig. 7 SS6638-27G Efficiency (L=47H CD54)
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
1.0 0.9 0.8
1.0 0.9
Start up
0.8
Start up
Input Voltage (V)
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18
Input Voltage (V)
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18
Hold on
Hold on
Output Current (mA) Fig. 8 SS6638-27G Start-Up & Hold-ON Voltage (L=47H CD54)
Output Current (mA) Fig. 9 SS6638-27G Start-Up & Hold-ON Voltage (L=100H CD54)
2.80 2.78 2.76 160
Switching Frequency (kHz)
140
Output Voltage (V)
2.74 2.72 2.70 2.68 2.66 2.64 2.62
120
100
80
60
2.60 -40
-20
0
20
40
60
80
100
40 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 10 SS6638-27G Output Voltage vs. Temperature
Temperature (C) Fig. 11 SS6638-27G Switching Frequency vs. Temperature
80
1.8
Maximum Duty Cycle (%)
78
SW Turn ON Resistance ()
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
76
74
72
70 -40
0.0 -20 0 20 40 60 80 100
-40
-20
0
20
40
60
80
100
Temperature (C) Fig. 12 SS6638-27G Maximum Duty Cycle vs. Temperature
Temperature (C) Fig. 13 SS6638-27G SW Turn ON Resistance vs. Temperature
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
45 40
3.1 3.0 2.9
VIN=2.0V VIN=1.8V
Output voltage VOUT(V)
Supply Current (A)
35 30 25 20 15 10
2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1
VIN=1.5V
VIN=1.2V VIN=0.9V
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
5 -40
-20
0
20
40
60
80
100
2.0
Temperature (C) Fig. 14 SS6638-27G Supply Current vs. Temperature
Output Current (mA)
Fig. 15 SS6638-30G Load Regulation (L=100H, CD54)
85 80 75
3.1 3.0 2.9
Output Voltage (V)
Efficiency (%)
2.8 2.7 2.6 2.5 2.4
VIN=1.2V
VIN=1.5V
VIN=1.8V
VIN=2.0V
70 65 60 55 50 0 20 40 60 80 100 120 140 160 180
VIN=1.8V VIN=1.5V VIN=0.9V VIN=1.2V
VIN=2.0
2.3 2.2 0
VIN=0.9V
20 40 60 80 100 120 140 160 180 200 220
Output Current (mA)
Output Current (mA)
Fig. 16 SS6638-30G Efficiency (L=100H, CD54)
Fig. 17 SS6638-30G Load Regulation (L=47H CD54)
85 80 75
1.0 0.9 0.8
Start up
Input Voltage (V)
Efficiency (%)
0.7 0.6 0.5 0.4 0.3 0.2
70 65
Hold on
VIN=2.0V
60 55
VIN=1.8V VIN=1.5V VIN=0.9V VIN=1.2V
50 75 100 125 150 175 200 225
0.1 0.0 0 2 4 6 8 10 12 14 16 18 20
50
0
25
Output Current (mA)
Fig. 18
SS6638-30G Efficiency (L=47H CD54)
Fig. 19
Output Current (mA) SS6638-30G Start-up & Hold-on Voltage (L=100H CD54)
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20
3.10
Start up
3.08 3.06
Output Voltage (V)
Input Voltage (V)
3.04 3.02 3.00 2.98 2.96 2.94 2.92 2.90 -40 -20 0 20
No Load
Hold on
40
60
80
100
Output Current (mA) Fig. 20 SS6638-30G Start-up & Hold-on Voltage (L=47H CD54) Fig. 21
Temperature (C) SS6638-30G Output Voltage vs. Temperature
80
160
Switching Frequency (kHz)
140
120
Maximum Duty Cycle (%)
0 20 40 60 80 100
78
76
100
74
80
72
60
40 -40
-20
70 -40
-20
0
20
40
60
80
100
Fig. 22
Temperature (C) SS6638-30G Switching Frequency vs. Temperature
Fig. 23
Temperature (C) SS6638-30G Maximum Duty Cycle vs. Temperature
1.8 1.6
45 40 35 30 25 20 15 10
SW Turn ON Resistance ()
1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20 0 20 40 60 80 100
Supply Current (A)
1.4
5 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 24 SS6638-30G SW Turn ON Resistance vs. Temperature
Fig. 25
Temperature (C) SS6638-30G Supply Current vs. Temperature
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
3.4 3.3 3.2 90
VIN=2.0V
85 80
Output Voltage (V)
3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 0 25
Efficiency (%)
VIN=1.5V
VIN=1.8V
VIN=2.0V
75 70 65 60
VIN=1.2V
VIN=1.8V
VIN=1.2V VIN=0.9V
50 75 100 125 150 175 200 55
VIN=1.5V
VIN=0.9V
50 0 25 50 75 100 125 150 175 200
Output Current (mA) Fig. 26 SS6638-33G Load Regulation (L=100H, CD54) Fig. 27
Output Current (mA) SS6638-33G Efficiency (L=100H, CD54)
3.4 3.3 3.2
90 85 80
Output Voltage (V)
Efficiency (%)
3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 0 25
VIN=1.5V
VIN=1.8V
VIN=2.0V
75 70 65 60 55 50
VIN=2.0V
VIN=1.2V VIN=0.9V
50 75 100 125 150 175 200 225
VIN=1.5V VIN=0.9V VIN=1.2V
VIN=1.8V
45 40 0 25 50 75 100 125 150 175 200 225 250
Fig. 28
Output Current (mA) SS6638-33G Load Regulation (L=47H, CD54)
Output Current (mA) Fig. 29 SS6638-33G Efficiency (L=47H,CD54)
1.1 1.0
3.50 3.45
Output Voltage Vout (V)
0.9
Start up
3.40 3.35 3.30 3.25 3.20 3.15 3.10 3.05 3.00 -40 -20 0 20 40 60 80 100
Input Voltage (V)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20
No Load
Hold on
Fig. 30
Output Current (mA) SS6638-33G Start-up & Hold-on Voltage (L=100H CD54)
Temperature (C) Fig. 31 SS6638-33G Output Voltage vs. Temperature
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
80
160
Switching Frequency (kHz)
140
120
Maximum Duty Cycle (%)
0 20 40 60 80 100
78
76
100
74
80
72
60
40 -40
-20
70 -40
-20
0
20
40
60
80
100
Fig. 32
Temperature (C) SS6638-33G Switching Frequency vs. Temperature
Fig. 33
Temperature (C) SS6638-33G Maximum Duty Cycle vs. Temperature
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20 0 20 40 60 80 100
45 40
SW Turn ON Resistance ()
Supply Current IDD1 (A)
35 30 25 20 15 10 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 34 SS6638-33G SW Turn ON Resistance vs. Temperature
Fig. 35
Temperature (C) SS6638-33G Supply Current vs. Temperature
4.6 4.4 4.2
90 85 80
Output Voltage (V)
4.0
Efficiency (%)
VIN=3.0V
3.8
VIN=1.5V
3.6 3.4 3.2
75 70
VIN=3.0V
VIN=2.0V
65 60 55 50
VIN=0.9V VIN=2.0V VIN=1.5V VIN=1.2V
VIN=0.9V
3.0 2.8 2.6 2.4 2.2 0 50
VIN=1.2V
100
150
200
250
300
350
400
0
50
100
150
200
250
300
350
400
Fig. 36
Output Current (mA) SS6638-45G Load Regulation (L=100H)
Fig. 37
Output Current (mA) SS6638-45G Efficiency (L=100H)
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
4.6 4.4 4.2
1.6 1.4 1.2
Output Voltage (V)
Input Voltage (V)
4.0
VIN=3.0V
3.8
Start up
1.0 0.8 0.6 0.4 0.2 0.0
VIN=1.5V
3.6 3.4 3.2
VIN=2.0V
Hold on
VIN=0.9V
3.0 2.8 2.6 2.4 2.2 0 50
VIN=1.2V
100
150
200
250
300
350
400
0
5
10
15
20
Fig. 38
Output Current (mA) SS6638-45G Load Regulation (L=100H)
Fig. 39
Output Current (mA) SS6638-45G Start-up & Hold-On Voltage (L=100H)
5.0 4.9 4.8 4.7 4.6
90 80 70 60 50 40 30 20 10 -40 -20 0 20 40 60 80 100
No Load
4.5 4.4 4.3 4.2 4.1 4.0 -40
-20
0
20
40
60
80
100
Fig. 40
Temperature (C) SS6638-45G Output Voltage vs. Temperature
Supply Current (A)
Output Voltage (V)
Fig. 41
Temperature (C) SS6638-45G Supply Current vs. Temperature
80
160
Switching Frequency (kHz)
140
120
Maximum Duty Cycle (%)
0 20 40 60 80 100
78
76
100
74
80
72
60
40 -40
-20
70 -40
-20
0
20
40
60
80
100
Fig. 42
Temperature (C) SS6638-45G Switching Frequency vs. Temperature
Fig. 43
Temperature (C) SS6638-45G Maximum Duty Cycle vs. Temperature
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
1.8 1.6
5.5 5.0
SW Turn ON Resistance ()
Output Voltage (V)
1.4 1.2 1.0 0.8 0.6 0.4
4.5
VIN=2.0V
4.0 3.5 3.0 2.5 2.0
VIN=3.0V
VIN=1.5V VIN=1.2V VIN=0.9V
0.2 0.0
1.5
-40 -20 0 20 40 60 80 100
0
50
100
150
200
250
300
350
400
Temperature (C) Fig. 44 SS6638-45G SW Turn ON Resistance vs. Temperature
Fig. 45
Output Current (mA) SS6638-50G Load Regulation ( L=100H CD54)
100 90
5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0
Output Voltage (V)
80
VIN=3.0V VIN=2.0V
Efficiency (%)
70 60
VIN=2.0V
VIN=3.0V
VIN=0.9V
50 40 30 20
VIN=1.5V VIN=1.2V
VIN=1.5V VIN=1.2V VIN=0.9V
0
50
100
150
200
250
300
350
400
1.5 0
50
100
150
200
250
300
350
400
Fig. 46
Output Current (mA) SS6638-50G Efficiency (L=100H CD54)
Output Current (mA) Fig. 47 SS6638-50G Load Regulation (L=47H CD54)
90 1.8 85 1.6 80 1.4
Efficiency (%)
75 70 65 60 55
Input Voltage (V)
1.2 1.0
VIN=3.0V
Start up
0.8 0.6
VIN=2.0V VIN=0.9V VIN=1.5V VIN=1.2V
Hold on
0.4 0.2 0.0
50 45 0
50
100
150
200
250
300
350
400
0
2
4
6
8
10
12
14
16
18
20
Output Current (mA) Fig. 48 SS6638-50G Efficiency (L=47H CD54)
Output Current (mA)
Fig. 49 SS6638-50G Start-up & Hold-on Voltage (L=100H CD50)
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
5.3 160 5.2
Output Voltage VOUT (V)
5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 -40
Switching Frequency (kHz)
60 80 100
140
No Load
120
100
80
60
-20
0
20
40
40 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 50 SS6638-50G Output Voltage vs. Temperature
Fig. 51
Temperature (C) SS6638-50G Switching Frequency vs. Temperature
80
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Maximum Duty Cycle (%)
78
76
74
72
70 -40
SW Turn ON Resistance ()
0.0 -20 0 20 40 60 80 100
-40
-20
0
20
40
60
80
100
Fig. 52
Temperature (C) SS6638-50G Maximum Duty Cycle vs. Temperature
Temperature (C) Fig. 53 SS6638-50G SW Turn ON Resistance vs. Temperature
100 90 80
VOUT 50mV/div
Supply Current IDD1 (A)
70 60 50
100mA
40
Load Step
30 20 10 -40
50mA/div
-20
0
20
40
60
80
100
Fig. 54
Temperature (C) SS6638-50G Supply Current vs. Temperature
Fig. 55 Load Transient Response (L1=100H, C2=47F, VIN=2V)
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SS6638G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
VOUT 20mv/div
VIN 0.5V/div
Fig. 56
Line Transient Response (L1=100H, C2=47F)
BLOCK DIAGRAM
SW
VOUT 1M
1.25V REF.
+
Enable GND
OSC, 100KHz
PIN DESCRIPTIONS
PIN 1 : GND - Ground. Must be low impedance; solder directly to ground plane. PIN 2 : VOUT - IC supply pin. Connect VOUT to the converter output. PIN 3 : SW - Internal drain of N-MOSFET switch.
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SS6638G
APPLICATION INFORMATION
GENERAL DESCRIPTION
The SS6638G PFM (pulse frequency modulation) converter IC combines a switch mode converter, N-channel power MOSFET, precision voltage reference, and voltage detector in a single monolithic device. It offers both extreme low quiescent current, high efficiency, and very low gate threshold voltage to ensure start-up with low battery voltage (0.8V typ.). Designed to maximize battery life in portable products, it minimizes switching losses by only switching as needed to service the load. PFM converters transfer a discrete amount of energy per cycle and regulate the output voltage by modulating the switching frequency with a constant pulse width. Switching frequency depends on load, input voltage, and inductor value, and it can range up to 100kHz. The SW on-resistance is typically 1 to 1.5 to minimize switching losses. When the output voltage drops, the error comparator enables the 100KHz oscillator that turns the MOSFET on for about 7.5s and off for 2.5s. Turning on the MOSFET allows inductor current to ramp up, storing energy in a magnetic field. When The MOSFET turns off, inductor current is forced through the diode to the output capacitor and load. As the stored energy is depleted, the current ramps down until the diode turns off. At this point, the inductor may ring due to residual energy and stray capacitance. The output capacitor stores charge when the current flowing through the diode is high, and releases it when current is low, thereby maintaining a steady voltage across the load. As the load increases, the output capacitor discharges faster and the error comparator initiates cycles sooner, increasing the switching frequency. The maximum duty cycle ensures adequate time for energy transfer to the output during the second half of each cycle. Depending on the circuit, PFM converters operate in either discontinuous mode or continuous conduction mode. Continuous conduction mode means that the inductor current does not ramp to zero during each cycle.
VIN
IIN SW
ID
IOUT VOUT
+ EXT Isw Ico
SS6638G
VEXT
IIN
IPK
ISW
Charge Co. ID TDIS Discharge Co. IOUT
VSW
t
Discontinuous Conduction Mode
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SS6638G
VEXT
fsw =
IIN
IPK IV
x TON (VOUT + VD - VSW ) VIN - VSW x )] [1 + ( 2 VOUT + VD - VSW 1 VOUT + VD - VIN TON VOUT + VD - VSW
1
(VOUT + VD - VIN)
ISW
where Vsw = switch drop and is proportional to output current.
ID IOUT
INDUCTOR SELECTION To operate as an efficient energy transfer element, the inductor must fulfill three requirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst-case condition of minimum input voltage and switch ON time. Second, the inductance must also be high enough so the maximum current rating of the SS6638 and inductor are not exceeded at the other worst-case condition of maximum input voltage and ON time. Lastly, the inductor must have sufficiently low DC resistance so excessive power is not lost as heat in the windings. Unfortunately this is inversely related to physical size. Minimum and maximum input voltage, output voltage and output current must be established before an inductor can be selected. In discontinuous mode operation, at the end of the switch ON time, peak current and energy in the inductor build according to
Ron + Rs Vin Ton) IPK = 1 - exp( - L Ron + Rs x VIN (TON) 1 - 2 L VIN TON L
VSW
t
Continuous Conduction Mode
At the boundary between continuous and discontinuous mode, output current (IOB) is determined by
VIN 1 VIN TON(1 - x ) IOB = VOUT + VD 2 L
where VD is the diode drop, x = (RON+Rs)Ton/L. RON= Switch turn on resistance, Rs= Inductor DC resistance TON = Switch ON time In the discontinuous frequency (Fsw) is
Fsw =
mode,
the
switching
2(L)(VOUT + VD - VIN)(IOUT) (1 + x ) VIN 2 x TON 2
In the continuous mode, the switching frequency is
(Simple losses equation),
where x=(RON+RS)TON/L
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SS6638G
EL = 1 L x IPK 2 2
VOUT + VD - VSW x IPK = - IOUT + VIN - VSW 2 x VIN - VSW TON 1 - 2L 2
Power required from the inductor per cycle must be equal or greater than
PL/FSW = (VOUT + VD - VIN)(IOUT)( 1 FSW )
Valley current (Iv) is
VIN - VSW VOUT + VD - VSW x Iv = - IOUT - x VIN - VSW 2 2L x TON 1 - 2
in order for the converter to regulate the output. When loading is over IOB, PFM converter operates in continuous mode. Inductor peak current can be derived from Table 1 Indicates resistance and height for each coil. Inductance Power Inductor Type ( H ) 22 Coilcraft SMT Type (www.coilcraft.com) DS1608 47 100 DO3316 Sumida SMT Type CD54 Hold Hold SMT Type PM54 SMT Type PM75 22 47 47 100 47 100 33
Resistance () 0.10 0.18 0.38 0.08 0.14 0.25 0.50 0.25 0.50 0.11
Rated Current (A) 0.7 0.5 0.3 2.7 1.8 0.7 0.5 0.7 0.5 1.2
Height (mm) 2.9
5.2 4.5 4.5 5.0
CAPACITOR SELECTION
A poor choice for an output capacitor can result in poor efficiency and high output ripple. Ordinary aluminum electrolytics, while inexpensive, may have unacceptably poor ESR and ESL. There are low ESR aluminum capacitors for switch mode DC-DC converters which work much better than general proposetypes. Tantalum capacitors provide still better performance but are more expensive. OS-CON capacitors have extremely low ESR in a small size. If capacitance is reduced, output ripple will increase. Most of the input supply is provided by the input bypass capacitor; the capacitor voltage rating
should be at least 1.25 times greater than the maximum input voltage.
DIODE SELECTION
Speed, forward drop, and leakage current are the three main considerations in selecting a rectifier diode. Best performance is obtained with a Schottky rectifier diode, such as the 1N5818, or the SS13 and B0530W in surface mount packages. For lower output power a 1N4148 can be used although efficiency and start-up voltage will suffer substantially.
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SS6638G
COMPONENT POWER DISSIPATION
Operating in discontinuous mode, power loss in the winding resistance of inductor can be approximated to
PD L = 2 TON VOUT + VD (POUT ) (Rs ) 3 L VOUT
VD = Diode drop. The power dissipated due to the switch loss is
PDsw = 2 TON VOUT + VD - VIN (POUT ) (RON) 3 L VOUT
The power dissipated in the rectifier diode is
VD PDD = (POUT) VOUT
where POUT=VOUT xIOUT ; Rs=Inductor DC R;
PHYSICAL DIMENSIONS (unit: mm)
SOT-23-3 (GU)
D
SYMBOL A
0.25
MIN 0.95 0.05 0.90 0.30 0.08 2.80 2.60 1.50 0.95 BSC 1.90 BSC 0.30 0.60 REF 0
MAX 1.45 0.15 1.30 0.50 0.22 3.00 3.00 1.70
A1 A2 b c D E E1
E1 e e1
E
c L L1
A2
A A1 b
e e1 L L1
0.60
8
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SS6638G
PHYSICAL DIMENSIONS (unit: mm) (Continued)
SOT-89-3 (GX)
D D1 C A
SYMBOL A B B1 C
MIN 1.40 0.44 0.36 0.35 4.40 1.50 2.29 1.50 BSC 3.00 BSC 3.94 0.89
MAX 1.60 0.56 0.48 0.44 4.60 1.83 2.60
H E
D D1 E
L e e1 B B1
e e1 H L
4.25 1.20
TO-92 (GZ)
SYMBOL A
A D
MIN 4.32 0.36 4.45 3.18 2.42 1.15 3.43 12.70 2.03
MAX 5.33 0.47 5.20 4.19 2.66 1.39 2.66
b D E e
b S E
e1 j L S
L
j
e1 e
Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties.
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