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SS6642G
3-Pin Simple Step-Up DC/DC Converter
FEATURES
A 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, 3.7V, 4.5V and 5V. Space-saving packages: SOT-23, SOT-89 and TO-92.
DESCRIPTION
The SS6642G 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, 3.7V, 4.5V or 5V. The SS6642G starts up from less than 0.9V input with 1mA load. A Pulse Frequency Modulation scheme optimizes performance for applications with light output loading and low input voltages. The output ripple and noise are lower when compared with circuits operating in PSM mode.
Pb-free, RoHS compliant.
APPLICATIONS
Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Suppliers. Portable Instruments.
The PFM control circuit operating at a 100KHz (max.) switching rate results in smaller passive components. The space saving SOT-23, SOT89 and TO-92 packages make the SS6642G an ideal choice for DC/DC converter for space conscious applications, such as pagers, electronic cameras, and wireless microphones.
TYPICAL APPLICATION CIRCUIT
VIN L1 100H D1 SS12 VOUT
SS6642-xxG + C1 SW 22F GND + VOUT C2 47F
One Cell Step-Up DC/DC Converter
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SS6642G
ORDERING INFORMATION
SS6642-XXXXXX Packing type TR: Tape and reel TB: Tube Package type GU: RoHS-compliant SOT-23 GX: RoHS-compliant SOT-89 GZ: RoHS-compliant TO-92
PIN CONFIGURATION
SOT-89 TOP VIEW 1: GND 2: VOUT 3: SW
1 2 3
Output voltage 27: 2.7V 30: 3.0V 33: 3.3V 37: 3.7V 45: 4.5V 50: 5.0V
TO-92 TOP VIEW 1: GND 2: VOUT 3: SW
1 2 3
SOT-23 TOP VIEW 1: GND 2: SW 3: VOUT 1
3
2
Example: SS6642-27GXTR 2.7V output version, in RoHS-compliant SOT-89 shipped on tape and reel.
SOT-23 MARKING
Part No. SS6642-27G SS6642-30G SS6642-33G SS6642-37G SS6642-45G SS6642-50G GU GM27P GM30P GM33P GM37P GM45P GM50P
SOT-89 MARKING
Part No. SS6642-27G SS6642-30G SS6642-33G SS6642-37G SS6642-45G SS6642-50G GX AM27P AM30P AM33P AM37P AM45P AM50P
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SS6642G
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 150C 260C
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
TEST CIRCUIT
VIN IIN L1 100H D1 SS12 VOUT
IS
SS6642 VOUT GND SW VSW
SS6642-xxG + C2 22F SW GND VOUT + C1 47F
VS
Fig. 1 Test Circuit 1
Fig. 2 Test Circuit 2
SS6642 100W VS VOUT GND SW FOSC
Fig. 3 Test Circuit 3
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SS6642G
ELECTRICAL CHARACTERISTICS
(Note1) PARAMETER TEST CONDITIONS
SS6642-27G SS6642-30G SS6642-33G Output Voltage SS6642-37G SS6642-45G SS6642-50G Start-Up Voltage Min. Hold-on Voltage No-Load Input Current VIN=1.8V VIN=1.8V VIN=2.0V V IN=2.0V VIN=3.0V VIN=3.0V 1 1 1 VSTART VHOLD IIN 15 42 50 60 65 2 IS1 70 90 A 1 VOUT
TEST CKT SYMBOL
(TA=25C, IOUT=10mA, unless otherwise specified)
MIN.
2.633 2.925 3.218 3.607 4.387 4.875
TYP.
2.700 3.000 3.300 3.700 4.500 5.000 0.8
MAX.
2.767 3.075 3.382 3.792 4.613 5.125 0.9 0.7
UNIT
V
IOUT=1mA, VIN:02V IOUT=1mA, VIN:20V IOUT=0mA SS6642-27G SS6642-30G SS6642-33G SS6642-37G SS6642-45G SS6642-50G VS=VOUT x 0.95 Measurement of the IC input current (VOUT pin) SS6642-27G SS6642-30G SS6642-33G SS6642-37G
V V A
Supply Current
7 7 7 7 2 IS2 7 7 A
Supply Current
SS6642-45G SS6642-50G VS=VOUT + 0.5V Measurement of the IC input current (VOUT pin)
SW Leakage Current
VSW=6V, VS=VOUT + 0.5V
2
0.5
A
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SS6642G
ELECTRICAL CHARACTERISTICS
PARAMETER TEST CONDITIONS
SS6642-27G SS6642-30G SS6642-33G SW Switch-On Resistance SS6642-37G SS6642-45G SS6642-50G VS=VOUT x 0.95, VSW=0.4V VS=VOUT x 0.95 Oscillator Duty Cycle Measurement of the SW pin waveform VS=VOUT x 0.95 Max. Oscillator Freq. Efficiency Measurement of the SW pin waveform 3 1 FOSC 80 105 85 130 KHz % 3 DUTY 65 75 85 % 2 RON
(Continued)
TEST CKT
SYMBOL
MIN.
TYP.
2.2 2.1 2.0 2.0 1.9 1.9
MAX.
UNIT
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
Test circuit refer to typical application circuit Capacitor (C2) : 47 F (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 SS6642-27 Load Regulation (L=100H CD54)
Output current (mA) Fig. 5 SS6642-27 Efficiency (L=100H CD54)
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
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
SS6642-27 Load Regulation (L=47H CD54)
Fig. 7
Output current (mA) SS6642-27 Efficiency (L=47H CD54)
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
Fig. 8
Output Current (mA) SS6642-27 Start-Up & Hold-ON Voltage (L=47H CD54)
Output Current (mA) Fig. 9 SS6642-27 Start-Up & Hold-ON Voltage (L=100H CD54)
2.80 2.78 160
Switching Frequency (kHz)
2.76
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 SS6642-27 Output Voltage vs. Temperature
Temperature (C) Fig. 11 SS6642-27 Switching Frequency vs. Temperature
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
80
(Continued)
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
Temperature (C) Fig. 12 SS6642-27 Maximum Duty Cycle vs. Temperature
Temperature (C) Fig. 13 SS6642-27 SW Turn ON Resistance vs. Temperature
45 40 35 30 25 20 15 10
3.1 3.0 2.9
VIN=2.0V VIN=1.8V
Output voltage VOUT(V)
Supply Current (A)
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 SS6642-27 Supply Current vs. Temperature
Output Current (mA)
Fig. 15 SS6642-30 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 SS6642-30 Efficiency (L=100H, CD54)
Fig. 17 SS6642-30 Load Regulation (L=47H CD54)
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TYPICAL PERFORMANCE CHARACTERISTICS
85 80 75
(Continued)
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
SS6642-30 Efficiency (L=47H CD54)
Fig. 19
Output Current (mA) SS6642-30 Start-up & Hold-on Voltage (L=100H CD54)
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 SS6642-30 Start-up & Hold-on Voltage (L=47H CD54)
Temperature (C) Fig. 21 SS6642-30 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
Temperature (C) Fig. 22 SS6642-30 Switching Frequency vs. Temperature
Temperature (C) Fig. 23 SS6642-30 Maximum Duty Cycle vs. Temperature
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
45 40 35 30 25 20 15 10 5 -40
(Continued)
1.8 1.6
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
-20
0
20
40
60
80
100
Fig. 24
Temperature (C) SS6642-30 SW Turn ON Resistance vs. Temperature
Temperature (C) Fig. 25 SS6642-30 Supply Current vs. Temperature
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
0 25 50 75 100
VIN=1.5V
VIN=0.9V
50 75 100 125 150 175 200
55 50
125
150
175
200
Output Current (mA) Fig. 26 SS6642-33 Load Regulation (L=100H, CD54) Fig. 27
Output Current (mA) SS6642-33 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
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
50 45 40 0
25
50
75
100
125
150
175
200
225
250
Output Current (mA) Fig. 28 SS6642-33 Load Regulation (L=47H, CD54)
Output Current (mA) Fig. 29 SS6642-33 Efficiency (L=47H,CD54)
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
1.1 1.0
3.50 3.45
(Continued)
0.8
Output Voltage Vout (V)
0.9
Start up
3.40 3.35 3.30 3.25 3.20 3.15 3.10 3.05
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 20
No Load
Hold on
3.00 -40
-20
0
20
40
60
80
100
Output Current (mA) Fig. 30 SS6642-33 Start-up & Hold-on Voltage (L=100H CD54)
Temperature (C) Fig. 31 SS6642-33 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
60
72
40 -40
-20
70 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 32 SS6642-33 Switching Frequency vs. Temperature
Fig. 33
Temperature (C) SS6642-33 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
Fig. 34
Temperature (C) SS6642-33 SW Turn ON Resistance vs. Temperature
Temperature (C) Fig. 35 SS6642-33 Supply Current vs. Temperature
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4
0
(Continued)
90 85 80
Output Voltage (V)
VIN=1.2V VIN=1.8V
VIN=2.5V
75
Efficiency (%)
VIN =2.0V
70 65 60 55 50
VIN =2.5V VIN=1.2V VIN=1.8V VIN=0.9V
VIN=2.0V
VIN =0.9V
25 50 75 100 125 150 175 200 225 250 275
45 40 0 25 50 75 100 125 150 175 200 225 250
Output Current (mA) Fig. 36 SS6642-37 Load Regulation (L=100H)
Output Current (mA) Fig. 37 SS6642-37 Efficiency (100H)
3.8 3.7 3.6 3.5 3.4
90 85 80
Output Voltage (V)
3.2 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 0 25
VIN=1.8V
Efficiency (%)
3.3
VIN=2.5V VIN=2.0V
75 70 65 60 55 50
VIN=2.5V
VIN=1.8V VIN=0.9V VIN=1.2V
VIN=2.0V
VIN=1.2V
VIN=0.9V
50 75 100 125 150 175 200 225 250 275
45 40 0 25 50 75 100 125 150 175 200 225 250 275
Output Current (mA) Fig. 38 SS6642-37 Load Regulation (L=47H)
Output Current (mA) Fig. 39 SS6642-37 Efficiency (47H)
1.6 1.4 1.2
4.00 3.95 3.90 3.85
Input Voltage (V)
Start up
1.0 0.8 0.6 0.4 0.2 0.0
Output Voltage (V)
3.80 3.75 3.70 3.65 3.60 3.55 3.50 3.45
No Load
Hold on
0
5
10
15
20
3.40 -40
-20
0
20
40
60
80
100
Output Current (mA) Fig. 40 SS6642-37 Start-up & Hold-on Voltage (L=100H)
Temperature (C) Fig. 41 SS6642-37 Output Voltage vs. Temperature
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TYPICAL PERFORMANCE CHARACTERISTICS
80 160
(Continued)
Switching Frequency (KHz)
140 120 100 80 60 40 -40
Maximum Duty Cycle (%)
-20 0 20 40 60 80 100
78
76
74
72
70 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 42 SS6642-37 Switching Frequency vs. Temperature
Temperature (C) Fig. 43 SS6642-37 Maximum Duty Cycle vs Temperature
4.6 4.4 4.2
90 85 80
Output Voltage (V)
4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 0 50 100 150 200 250 300
VIN=1.5V VIN=2.0V
Efficiency (%)
VIN=3.0V
75 70
VIN=3.0V
VIN=0.9V
VIN=1.2V
65 60 55 50
VIN=0.9V VIN=1.2V VIN=2.0V VIN=1.5V
350
400
0
50
100
150
200
250
300
350
400
Output Current (mA) Fig. 44 SS6642-45 Load Regulation (L=100H)
Output Current (mA) Fig. 45 SS6642-45 Efficiency (L=100H)
4.6 4.4 4.2
1.6 1.4 1.2
Output Voltage (V)
3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 0 50
Input Voltage (V)
4.0
VIN=3.0V VIN=1.5V VIN=2.0V
Start up
1.0 0.8 0.6 0.4 0.2 0.0
Hold on
VIN=0.9V
VIN=1.2V
100
150
200
250
300
350
400
0
5
10
15
20
Output Current (mA) Fig. 46 SS6642-45 Load Regulation (L=100H)
Output Current (mA) Fig. 47 SS6642-45 Start-up & Hold-On Voltage (L=100H)
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0
(Continued)
90 80
Supply Current (A)
40 60 80 100
Output Voltage (V)
70 60 50 40 30 20 10
No Load
-40
-20
0
20
-40
-20
0
20
40
60
80
100
Temperature (C) Fig. 48 SS6642-45 Output Voltage vs. Temperature
Temperature (C) Fig. 49 SS6642-45 Supply Current vs. Temperature
80 160
Switching Frequency (kHz)
140
120
Maximum Duty Cycle (%)
78
76
100
74
80
60
72
40 -40
-20
0
20
40
60
80
100
70 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 50 SS6642-45 Switching Frequency vs. Temperature
Temperature (C) Fig. 51 SS6642-45 Maximum Duty Cycle vs. Temperature
1.8 1.6
5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 -40 -20 0 20 40 60 80 100 0 50 100 150 200 250 300 350 400
SW Turn ON Resistance ()
Output Voltage (V)
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
VIN=2.0V
VIN=3.0V
VIN=1.5V VIN=1.2V VIN=0.9V
Temperature (C) Fig. 52 SS6642-45 SW Turn ON Resistance vs. Temperature
Output Current (mA) Fig. 53 SS6642-50 Load Regulation ( L=100H CD54)
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TYPICAL PERFORMANCE CHARACTERISTICS
100 90 5.5 5.0
(Continued)
Output Voltage (V)
80
4.5 4.0 3.5 3.0 2.5 2.0 1.5 0
Efficiency (%)
70 60 50 40 30 20
VIN=2.0V
VIN=3.0V
VIN=2.0V VIN=0.9V VIN=1.5V VIN=1.2V
VIN=3.0V
VIN=1.5V VIN=1.2V VIN=0.9V
0
50
100
150
200
250
300
350
400
50
100
150
200
250
300
350
400
Fig. 54
Output Current (mA) SS6642-50 Efficiency (L=100H CD54)
Output Current (mA) Fig. 55 SS6642-50 Load Regulation (L=47H CD54)
90 85 80 1.4 1.8 1.6
Input Voltage (V)
Efficiency (%)
75 70 65 60 55 50 45 0
1.2 1.0 0.8 0.6 0.4 0.2
VIN=3.0V VIN=2.0V VIN=0.9V VIN=1.5V VIN=1.2V
100 150 200 250 300 350 400
Start up Hold on
50
0.0
0
2
4
6
8
10
12
14
16
18
20
Output Current (mA) Fig. 56 SS6642-50 Efficiency (L=47H CD54)
Output Current (mA)
Fig. 57 SS6642-50 Start-up & Hold-on Voltage (L=100H CD50)
5.3 5.2 160
Output Voltage VOUT (V)
5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 -40 -20 0 20 40 60 80 100
Switching Frequency (kHz)
140
No Load
120
100
80
60
Temperature (C) Fig. 58 SS6642-50 Output Voltage vs. Temperature
40 -40
-20
0
20
40
60
80
100
Temperature (C) Fig. 59 SS6642-50 Switching Frequency vs. Temperature
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SS6642G
TYPICAL PERFORMANCE CHARACTERISTICS
80
(Continued)
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 ()
-20
0
20
40
60
80
100
0.0
-40
-20
0
20
40
60
80
100
Temperature (C) Fig. 60 SS6642-50 Maximum Duty Cycle vs. Temperature
Temperature (C) Fig. 61 SS6642-50 SW Turn ON Resistance vs. Temperature
100 90 80
VOUT 50mV/div
Supply Current IDD1 (A)
70 60 50 40 30 20 10 -40
10mA Load Step 50mA/div
-20
0
20
40
60
80
100
Temperature (C) Fig. 62 SS6642-50 Supply Current vs. Temperature
Fig. 63 Load Transient Response (L1=100H, C2=47F, VIN=2V)
VOUT 20mv/div
VIN 0.5V/div
Fig. 64 Line Transient Response (L1=100H, C2=47F)
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SS6642G
BLOCK DIAGRAM
VOUT 1M
1.25V REF.
SW
+
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 regulator output. PIN 3 : SW -Drain of the internal N-channel MOSFET switch.
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SS6642G
APPLICATION INFORMATION
GENERAL DESCRIPTION The SS6642G PFM (pulse frequency modulation) controller IC combines a switch-mode regulator, Nchannel power MOSFET, precision voltage reference, and voltage detector in a single monolithic device. It offers extremely low quiescient 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 controllers transfer a discrete amount of energy per cycle and regulate the output voltage by modulating the switching frequency with a constant turn-on time. Switching frequency depends on load, input voltage, and inductor value, and it can range up to 100KHz. The SW on-resistance is typically 1.9 to 2.2 to minimize switch losses. When the output voltage drops, the error comparator enables the 100kHz oscillator that turns on the MOSFET for around 7.5us and off for 2.5us. 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 the 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, a PFM controller can operate in either discontinuous mode or continuous conduction mode. Continuous conduction mode means that the inductor current does not ramp down to zero during each cycle.
VIN IIN SW + EXT Isw Ico VOUT
ID
IOUT
VEXT
IIN
IPK
ISW
Charge Co. ID TDIS Discharge Co. IOUT
VSW
t
Discontinuous Conduction Mode
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SS6642G
VEXT
In the continuous mode, the switching frequency is
fSW = 1 (VOUT + VD - VIN) TON (VOUT + VD - VSW ) x VIN - VSW * [1 + ( )] 2 VOUT + VD - VSW 1 VOUT + VD - VIN TON VOUT + VD - VSW
IIN
IPK
ISW
where Vsw = switch drop and is proportional to output current.
IOUT
ID
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 that the maximum current rating of the SS6642 and the inductor are not exceeded at the other worstcase 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 in advance and then the 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 IPK = * TON) * 1 - exp( - L RON + Rs x VIN * (TON) * 1 - 2 L VIN TON L
VSW
t
Continuous Conduction Mode
Continuous Conduction Mode
At the boundary between continuous and discontinuous modes, output current (IOB) is determined by
VIN 1 VIN IOB = * TON * (1 - x ) * * VOUT 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 mode, the switching frequency (Fsw) is Fsw =
2 * (L) * (VOUT + VD - VIN) * (IOUT) VIN 2 x TON 2 (1 + x )
(simple loss equation),
TON L
where x = (RON + RS ) *
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SS6642G
EL =
1 L x Ipk 2 2
The power supplied by the inductor per cycle must be equal to or greater than
PL/fSW = (VOUT + VD - VIN) * (IOUT) * ( 1 ) fsw
When loading is over IOB, the PFM controller operates in continuous mode. Inductor peak current can be derived from
x VOUT+ VD - VSW x VIN- VSW IPK = - * IOUT+ * TON * 1- VIN- VSW 2 2L 2
in order for the converter to regulate the output.
Valley current (Iv) is
VOUT+ VD - VSW x VIN- VSW x IV = - * IOUT- * TON* 1- 2L 2 VIN- VSW 2
Table 1 Indicates resistance and height for each coil. Power Inductor Type Inductance ( H ) 22 Coilcraft SMT Type (www.coilcraft.com) DO3316 Sumida SMT Type CD54 Hold SMT Type PM54 Hold SMT Type PM75 DS1608 47 100 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 5.2 4.5 4.5 5.0 2.9 Height (mm)
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 types. Tantalum capacitors provide still better performance but are more expensive. OSCON capacitors have extremely low ESR and small size. If capacitance is reduced, output ripple will increase.
Most of the input supply is applied to the input bypass capacitor, so 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 Schottky rectifier diodes such as the 1N5819. SSC also has Schottkies for surface-mount. For lower output power a 1N4148 can be used, although efficiency and start-up voltage will suffer substantially.
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SS6642G
Component Power Dissipation Operating in discontinuous mode, power loss in the winding resistance of the inductor can be approximated to
PD L = 2 TON VOUT + VF * (POUT ) * (RD ) * 3 L VOUT
The power dissipated in the MOSFET switch 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 * IOUT; RS=Inductor DC R; VD = Diode drop.
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SS6642G
PHYSICAL DIMENSIONS
(unit: mm)
All package options are Pb-free, RoHS compliant.
SOT-23 (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
SOT-89 (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
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SS6642G
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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