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AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
FEATURES
! ! ! ! ! ! !
DESCRIPTION
The AIC1638 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, or 5V. The AIC1638 starts up from below 0.9V input with 1mA load. 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 the circuits operating in PSM mode. The PFM control circuit operating in 100KHz (max.) switching rate results in smaller passive components. The space saving SOT-89 and TO-92 packages make the AIC1638 an ideal choice of DC/DC converter for space conscious applications, like pagers, electronic cameras, and wireless microphones
Guaranteed Start-Up from below 0.9 V. High Efficiency. Low Quiescent Current. Few Number of External Components needed. Low Ripple and Low Noise. Fixed Output Voltage: 2.7V, 3.0V, 3.3V, and 5V. Space Saving SOT-89 and TO-92 Packages.
APPLICATIONS
! ! ! ! ! !
Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Suppliers. Portable Instruments.
TYPICAL APPLICATION CIRCUIT
VIN + C2 47F L1 88H D1 VOUT
SW
AIC1638-27 AIC1638-30 AIC1638-33 AIC1638-50 GND
VOUT + C1 22F
One Cell Step-Up DC/DC Converter
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
1
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
ORDERING INFORMATION
AIC1638- XXX
ORDER NUMBER
PACKAGE TYPE X: SOT-89 Z: TO-92 TEMPERATURE RANGE C: -20C+80C OUTPUT VOLTAGE 27: 2.7V 30: 3.0V 33: 3.3V 50: 5.0V
AIC1638-27CZ AIC1638-30CZ AIC1638-33CZ AIC1638-50CZ (TO-92) AIC1638-27CX AIC1638-30CX AIC1638-33CX AIC1638-50CX (SOT-89)
PIN CONFIGURATION
TOP VIEW 1: GND 2: VOUT 3: SW
1
2
3
TOP VIEW 1: GND 2: VOUT 3: SW
1 2 3
ABSOLUATE MAXIMUM RATINGS
Supply Voltage .....................................................................................12V ..............................................................................0.6A SW pin Voltage ............................................................................................12V SW pin Switch Current Power Dissipation .................................................................................500mW
Operating Temperature Range ..........................................................-20C to 80 C Storage Temperature Range ......................................................... -65C to 150 C Lead Temperature (Sordering 10 Sec.) .........................................................260C
TEST CIRCUIT
AIC1638 2.5V VOUT GND SW
100 FOUT
Oscillator Test Circuit
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
2
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage
(Ta=25C, IO=10mA, Unless otherwise specified)
SYMBOL
TEST CONDITIONS
VIN=1.8V VIN=1.8V VIN=2.0V VIN=3.0V
MIN.
2.633 2.925 3.218 4.875
TYP.
2.700 3.000 3.300 5.000
MAX.
2.767 3.075 3.382 5.125 8
UNIT
V
VOUT
Input Voltage Start-Up Voltage Min. Hold-on Voltage No-Load Input Current Supply Current IOUT=1mA, VIN:02V IOUT=1mA, VIN:20V IOUT=0mA VIN=VOUT x 0.95 Measurement of the IC input current
VIN VSTART VHOLD IIN IDD1 15 42 50 60 90 7 0.8
V V V A A
0.9 0.7
Supply Current
VIN=VOUT + 0.5V Measurement of the IC input current
IDD2
A
SW Leakage Current SW Switch-On Resistance
VSW =10V, VIN=VOUT + 0.5V VIN=VSW x 0.95, VSW =0.4V RON 1.3 1.2 1.1 1 65 75
0.5
A
Oscillator Duty Cycle
VIN=VOUT x 0.95 Measurement of the IC input current
DUTY
85
%
Max. Oscillator Freq.
VIN=VOUT x 0.95 Measurement of the IC input current
FOSC
80
105
130
KHz
Efficiency
85
%
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
3
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS
Capacitor (C1) : 47 F (Tantalum Type) Diode (D1) : 1N5819 Schottky Type
AIC1638-27 Load Regulation (L=100H CD54)
2.8 85
AIC1638-27 Efficiency (L=100H CD54)
2.7
80
Output voltage (V)
VIN=1.2V
2.5
Efficiency (%)
2.6
VIN=1.5V
VIN=1.8V
VIN=2.0V
75
70
VIN=1.8V
VIN=2.0V
2.4
65
VIN=1.5V VIN=0.9V
60
2.3
VIN=0.9V
2.2 0 55 20 40 60 80 100 120 140 160 180 0 20 40 60
VIN=1.2V
80 100 120 140 160 180
Output Current (mA)
Output current (mA)
AIC1638-27 Load Regulation (L=47H CD54)
2.8
AIC1638-27 Efficiency
85 80
(L=47H CD54)
2.7
75
Output voltage (V)
2.6
Efficiency (%)
VIN=1.2V
2.5
VIN=1.5V
VIN=1.8V
VIN=2.0V
70 65 60
VIN=2.0V VIN=1.8V
2.4
VIN=1.2V VIN=0.9V
VIN=1.5V
55
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)
Output current (mA)
AIC1638-27 Start-Up & Hold-ON Voltage (L=47H)
1.0 0.9 0.8
1.0 0.9
AIC1638-27 Start-Up & Hold-ON Voltage (L=100H)
Start up
0.8
Start up
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)
Input Voltage (V)
0.7
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)
Output Current (mA)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
4
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-27 Output Voltage vs Temperature
2.78 2.76
AIC1638-27 Switching Frequency vs Temperature
160 140
Output Voltage Vout (V)
2.74 2.72 2.70 2.68 2.66 2.64 2.62 -40
No Load
Switching Frequency (kHz)
120 100 80 60 40 20 -40
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-27 Maximum Duty Cycle vs Temperature
82 80 1.8 1.6
AIC1638-27 SW On Resistance vs Temperature
Maximum Duty Cycle (%)
SW Turn On Resistance ()
78 76 74 72 70 68 66 -40
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-27 Supply Current vs Temperature
52 48
AIC1638-30 Load Regulation (L=100H, CD54)
3.1 3.0 2.9
2.0V 1.5V 1.8V
Supply Current IDD1 (uA)
44 40 36 32 28 24 20 -40
Output voltage VOUT(V)
2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 0 10
1.2V VIN=0.9V
20 30 40 50 60 70 80 90 100 110 120 130 140
-20
0
20
40
60
80
100
Temperature (C)
Output Current (mA)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
5
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-30 Efficiency (L=100H, CD54)
85 80
AIC1638-30 Load Regulation (L=47H CD54)
3.1 3.0 2.9
Output Voltage (V)
Efficiency (%)
75 70 65 60
2.8 2.7 2.6 2.5 2.4 2.3
VIN=1.2V
VIN=1.5V
VIN=1.8V
VIN=2.0V
1.8V
2.0V
1.5V
55 50
VIN=0.9V
0 20 40 60
1.2V
80 100 120 140 160 180
VIN=0.9V
0 20 40 60 80 100 120 140 160 180 200 220
2.2
Output Current (mA)
Output Current (mA)
85 80 75
AIC1638-30 Efficiency (L=47H CD54)
1.0 0.9 0.8
AIC1638-30 Start-up & Hold-on Voltage (L=100H)
Start up
Input Voltage (V)
0.7 0.6 0.5 0.4 0.3 0.2 0.1
Efficiency (%)
70 65
Hold on
VIN=2.0V
60 55
VIN=1.8V VIN=1.5V VIN=1.2V
50 75 100 125 150 175 200 225
VIN=0.9V
50 0 25
0.0 0 2 4 6 8 10 12 14 16 18 20
Output Current (mA)
Output Current (mA)
AIC1638-30 Start-up & Hold-on Voltage (L=47uH)
1.0 0.9 0.8 3.06
AIC1638-30 Output Voltage vs Temperature
Start up
3.04
Output Voltage Vout (V)
No Load
3.02 3.00 2.98 2.96 2.94 2.92 2.90 -40
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
Hold on
-20
0
20
40
60
80
100
Output Current (mA)
Temperature (C)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
6
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-30 Switching Frequency vs Temperature
160
AIC1638-30 Maximum Duty Cycle vs Temperature
82
Switching Frequency (kHz)
Maximum Duty Cycle (%)
140 120 100 80 60 40 20 0 -40
80 78 76 74 72 70 68 66 -40
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-30 SW On Resistance vs Temperature
1.8 1.6
52 48
AIC1638-30 Supply Current vs Temperature
SW Turn On Resistance ()
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40
Supply Current IDD1 (A)
-20 0 20 40 60 80 100
44 40 36 32 28 24 20 -40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-33 Load Regulation (L=100H, CD54)
3.4 3.3 3.2 90
AIC1638-33 Efficiency (L=100H, CD54)
VIN=2.0V
85 80
Output Voltage (V)
Efficiency (%)
3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 0 25
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)
Output Current (mA)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
7
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-33 Load Regulation (L=47H, CD54)
3.4 3.3 3.2 90 85 80
AIC1638-33 Efficiency (L=47H,CD54)
Output Voltage (V)
3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 0 25
VIN=1.5V
Efficiency (%)
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
Output Current (mA)
Output Current (mA)
AIC1638-33 Start-up & Hold-on Voltage (L=100H)
1.1 1.0 3.50 3.45
AIC1638-33 Output Voltage vs Temperature
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
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
No Load
Hold on
60
80
100
Output Current (mA)
Temperature (C)
AIC1638-33 Switching Frequency vs Temperature
150 140 82 80
AIC1638-33 Maximum Duty Cycle vs Temperature
Switching Frequency (kHz)
130 120 110 100 90 80 70 60 50 -40 -20 0 20 40 60 80 100
Maximum Duty Cycle (%)
78 76 74 72 70 68 66 -40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
8
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-33 SW On Resistance vs Temperature
1.8 60 56
AIC1638-33 Supply Current vs Temperature
SW Turn On Resistance ()
1.6
Supply Current IDD1 (A)
-20 0 20 40 60 80 100
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40
52 48 44 40 36 32 28 24 -40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-50 Load Regulation ( L=100H,CD54)
5.5 5.0 100 90
AIC1638-50 Efficiency (L=100H,CD54)
Output Voltage (V)
4.5 4.0 3.5 3.0
Efficiency (%)
VIN=2.0V
VIN=3.0V
80 70 60
VIN=2.0V VIN=0.9V
VIN=3.0V
VIN=1.5V
50 40
VIN=1.5V VIN=1.2V
VIN=1.2V
2.5 2.0 1.5
VIN=0.9V
30 20
0
50
100
150
200
250
300
350
400
0
50
100
150
200
250
300
350
400
Output Current (mA)
Output Current (mA)
AIC1638-50 Load Regulation (L=47H,CD54)
5.5 5.0 90 85 80
AIC1638-50 Efficiency (L=47H,CD54)
Output Voltage (V)
4.5
VIN=2.0V
4.0 3.5 3.0
Efficiency (%)
VIN=3.0V
75 70 65 60 55 50 45
VIN=3.0V
VIN=1.5V VIN=1.2V
VIN=2.0V VIN=0.9V VIN=1.5V VIN=1.2V
100 150 200 250 300 350 400
2.5
VIN=0.9V
2.0 1.5
0
50
100
150
200
250
300
350
400
0
50
Output Current (mA)
Output Current (mA)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
9
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
AIC1638-50 Start-up & Hold-on Voltage (L=100H)
1.8 1.6 5.3 5.2
AIC1638-50 Output Voltage vs Temperature
Output Voltage Vout (V)
1.4
5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 -40
No Load
Input Voltage (V)
1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 2 4 6 8 10 12 14 16 18 20
Start up
Hold on
-20
0
20
40
60
80
100
Output Current (mA)
AIC1638-50 Switching Frequency vs Temperature
150 82 80
Temperature (C)
AIC1638-50 Maximum Duty Cycle vs Temperature
Switching Frequency (kHz)
Maximum Duty Cycle (%)
-20 0 20 40 60 80 100
140 130 120 110 100 90 80 70 60 -40
78 76 74 72 70 68 66 64 -40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
AIC1638-50 SW On Resistance vs Temperature
1.6 100 90
AIC1638-50 Supply Current vs Temperature
SW Turn On Resistance ()
1.4
Supply Current IDD1 A)
-20 0 20 40 60 80 100
80 70 60 50 40 30 20 10 -40
1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
10
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
"
TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED)
VOUT
VOUT 50mV/div
20mv/div
VIN
Load Step 50mA/div
0.5V/div
Load Transient Response (L=100H, Co=47F, VIN=2V)
Line Transient Response
BLOCK DIAGRAM
SW
VOUT 1M
1.25V REF.
+
Enable GND
OSC, 100KHz
PIN DESCRIPTIONS
PIN1 : GND PIN2 : VOUT - Ground. Must be low impedance; sorder directly to ground plane. - IC supply pin. Connect VOUT to the regulator output. PIN3 : SW - Internal drain of N-MOSFET switch.
APPLICATION INFORMATION
GENERAL DESCRIPTION
AIC1638 PFM (pulse frequency modulation) controller ICs combine a switch mode regulator, N-channel power MOSFET, precision voltage reference, and voltage detector in a single monolithic device. They offer both extreme low quiescent current, high efficiency, and very low gate threshold voltage to ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
ensure start-up with low battery voltage ( 0.8V typ.). Designed to maximize battery life in portable products, and minimize switching losses by only switching as needed service the load. PFM controllers transfer a discrete amount of energy per cycle and regulate the output voltage by modulating switching frequency with the constant www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
11
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
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 to 1.5 to minimize switch losses. When the output voltage drops, the error comparator enables 100KHz oscillator that turns on the MOSFET around 7.5us and 2.5s off time. Turning on the MOSFET allows inductor current to ramp up, storing energy in a magnetic field. When MOSFET turns off that force inductor current through diode to the output capacitor and load. As the stored energy is depleted, the current ramp down until the diode turns off. At this point, inductor may ring due to residual energy and stray capacitance. The output capacitor stores charge when current flowing through the diode is high, and release 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 ensure adequate time for energy transfer to output during the second half each cycle. Depending on circuit, PFM controller can 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 + EXT Isw Ico VOUT
VEXT
IIN
IPK
ISW
ID
Charge Co. IOUT TDIS Discharge Co.
VSW
t
Discontinuous Conduction Mode
VEXT
ID
IOUT
IIN
IPK IV
ISW
ID IOUT
VSW
t
Continuous Conduction Mode
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
12
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
At the boundary between continuous and discontinuous mode, output current (IOB) is determined by VIN 1 VIN IOB = TON(1- x ) 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 mode, the switching frequency (fsw) is fsw = 2(L)(VOUT + VD - VIN)(IOUT) (1+ x VIN 2 x TON 2
Ron + Rs Vin IPK = Ton) 1 - exp( - L Ron + Rs x VIN (TON)1 - 2 L VIN (Simple losses equation), TON L where x=(RON+RS)TON/L 1 EL = L x Ipk2 2 Power required from the inductor per cycle must be equal or greater than 1 PL/fSW = (VOUT + VD - VIN)(IOUT)( ) fSW in order for the converter to regulate the output. When loading is over IOB, PFM controller operates in continuous mode. Inductor peak current can be derived from VOUT + VD - VSW x - IOUT + IPK = VIN - VSW 2 x VIN - VSW TON1 - 2L 2 Valley current (Iv) is VOUT + VD - VSW x VIN - VSW Iv = - IOUT - x 2L 2 VIN - VSW x TON1- 2
In the continuous mode, the switching frequency is fsw = 1 TON (VOUT + VD - VSW)
(VOUT + VD - VIN) [1+ x (
VIN - VSW )] 2 VOUT + VD - VSW
1 VOUT + VD - VIN TON VOUT + VD - VSW
where Vsw = switch drop and proportion to output current.
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 maximum current rating of AIC1638 and inductor are not exceed 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. But unfortunately this is inversely related to physical size. Minimum and Maximum input voltage, output voltage and output current must be established before and 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
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
13
AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
Table 1 Indicates resistance and height for each coil. Inductance ( H ) 22 DS1608 Coilcraft SMT Type (www.coilcraft.com) DO3316 47 Sumida SMT Type CD54 47 100 47 100 33 0.14 0.25 0.50 0.25 0.50 0.11 1.8 0.7 0.5 0.7 0.5 1.2 4.5 47 100 22 Resistance () 0.10 0.18 0.38 0.08 Rated Current (A) 0.7 0.5 0.3 2.7 5.2 2.9 Height (mm)
Power Inductor Type
Hold Hold
SMT Type PM54 SMT Type PM75
4.5 5.0
CAPACITOR SELECTION
A poor choice for a output capacitor can result in poor efficiency and high output ripple. Ordinary aluminum electrolytic, 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 propose unit. Tantalum capacitors provide still better performance at 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 supplied by the input bypass capacitor, the capacitor voltage rating should be at least 1.25 times greater than a maximum input voltage.
DIODE SELECTION
Speed, forward drop, and leakage current are the three main consideration in selecting a rectifier diode. Best performance is obtained with Schottky rectifier diode such 1N5819. Motorola makes MBR0530 in surface mount. For lower output power a 1N4148 can be used although efficiency and start-up voltage will suffer substantially.
COMPONENT POWER DISSIPATION
Operating in discontinuous mode, power loss in the winding resistance of inductor can be approximate equal to PDL = 2 TON VOUT + VD (Rs ) (POUT ) 3 L VOUT
where POUT=VOUT * IOUT ; Rs=Inductor DC R;
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
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AIC1638
3-PIN ONE-CELL STEP-UP DC/DC CONVERTER
SPEC NO: DS-1638-00 03/01/00
VD = Diode drop. The power dissipated in a switch loss is PDsw = 2 TON VOUT + VD - VIN (RON) (POUT ) 3 L VOUT
The power dissipated in rectifier diode is VD PDD = (POUT) VOUT
PHYSICAL DIMENSION
! SOT-89 (unit: mm)
D D1 C A
SYMBOL A B C D
MIN 1.40 0.36 0.35 4.40 1.62 2.29
MAX 1.60 0.48 0.44 4.60 1.83 2.60 1.50 (TYP.) 3.00 (TYP.)
H E
D1 E e
L e e1 B
e1 H L 3.94 0.89
4.25 1.20
SOT-89 MARKING Part No. AIC1638-27 AIC1638-30 AIC1638-33 AIC1638-50 Marking AN27 AN30 AN33 AN50
! TO-92 (unit: mm)
A L C E
SYMBOL A C
MIN 4.32
MAX 5.33 0.38 (TYP.)
e1 D
D E e1 L
4.40 3.17 1.27 (TYP.) 12.7
5.20 4.20
-
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
15

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