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AIC1647
White LED Step-Up Converter in SOT23
FEATURES
1.2MHz Fixed Frequency Current-Mode PWM Operation. Efficiency Up to 84% at VIN=4.2V, 3LEDs, ILED=20mA Drives Up to 6LEDs in series Low Supply Current: 70A Matches LED Current Require Tiny Inductors and Capacitors Tiny SOT23-5 Package
DESCRIPTION
AIC1647 is a fixed frequency step-up DC/DC converter designed to drive white LEDs with a constant current to provide backlight in handheld devices. Series connection of the LEDs provides identical LED currents resulting in uniform brightness. This configuration eliminates the need for ballast resistors. Low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. AIC1647 is a step-up PWM converter, which
APPLICATIONS
Cellular Phones PDAs Digital Still Cameras Handheld Devices White LED Display Backlighting
includes an internal N-channel MOSFET switch for high efficiency. The high switching frequency, 1.2MHz, allows the use of tiny external components, saves the layout space and cost. AIC1647 is available in a space-saving, 5-lead SOT-23-5 package.
TYPICAL APPLICATION CIRCUIT
3.3~4.2V C1 1F
L 6.8H VIN SHDN GND FB SW
D1 C2 1F
BZV55-B12 11.8V~12.2V
90
VIN=4.2V
85
Efficiency (%)
80 75 70
D2 R1 1K RFB 4.7 20mA
VIN=3.0V
VIN=3.6V
AIC1647
L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ105KA, TAIYO YUDEN
3 LEDs, 6.8H
65
L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM
60 0 5
LED Current (mA)
10
15
20
Fig. 1 Li-Ion Powered Driver with Over Voltage Protection for Three White LEDs
Analog Integrations Corporation
Si-Soft Research Center 3A1, No.1, Li-Hsin Rd. I, Science Park, Hsinchu 300, Taiwan, R.O.C. TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw
DS-1647P-03 010405
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AIC1647
ORDERING INFORMATION
AIC1647XXXX PACKING TYPE TR: TAPE & REEL BG: BAG PACKAGE TYPE V: SOT-23-5 C: Commercial P: Lead Free Commercial Example: AIC1647CVTR in SOT-23-5 Package & Tape & Reel Packing Type
1 2 3
ORDER NUMBER AIC1647CV&PV (SOT-23-5)
PIN CONFIGURATION
FRONT VIEW
VIN
5
SHDN
4
SW GND FB
MARKING Part No. AIC1647
CV 1647
PV 1647P
ABSOLUTE MAXIMUM RATINGS
Input Voltage (VIN) SW Voltage FB Voltage
SHDN Voltage
6V 33V 6V 6V -40C to 85C 125C -65C to 150C 260C
Operating Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering, 10 sec)
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
TEST CIRCUIT
L1 VIN C1 1F 10H VIN SHDN GND FB AIC1647
L1: 976AS-100M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ224KG, TAIYO YUDEN
D1 C2 SW D2
BZV55-B12 11.8V~12.2V
0.22F
ILED R1 1K RFB 4.7
2
AIC1647
ELECTRICAL CHARACTERISTICS
(V SHDN =3V, VIN=3V, TA=25C, unless otherwise specified.) (Note 1)
PARAMETER Minimum Operating Voltage Maximum Operating Voltage SYMBOL VIN VIN Switching Supply Current IIN Non switching V SHDN = 0V ERROR AMPLIFIER Feedback Voltage FB Input Bias Current OSCILLATOR Switching Frequency Maximum Duty Cycle POWER SWITCH SW ON Resistance Switch Leakage Current CONTROL INPUT
SHDN Voltage High SHDN Voltage Low
TEST CONDITIONS
MIN 2.5
TYP
MAX
UNIT V
5.5 1 70 0.1 5 100 1.0
V mA A
VFB IFB VFB=95mV
85
95 1
105
mV nA
fOSC DC
0.8 85
1.2 90
1.6
MHz %
RDS(ON) ISW(OFF) VSW=33V
1.4 0.1
5 1
A
VIH VIL
ON OFF
1.5 0.3
V V
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).
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AIC1647
TYPICAL PERFORMANCE CHARACTERISTICS
1.6
Switching Frequency (MHz)
0 50 100 150
95.0
Feedback Voltage (mV)
94.5 94.0 93.5 93.0 92.5 92.0 -50
1.4
1.2
1.0
0.8
0.6
Temperature (C) Fig. 2 Feedback Voltage vs. Temperature
0.4 -50
Fig. 3
Temperature (C) Switching Frequency vs. Temperature
0
50
100
150
70
1.6
FB=GND
60
FB=VIN
50
Supply Current (mA)
Non-Switching
Supply Current (A)
1.4
1.2
1.0
40
0.8
0.6
6
Switching
2 3 4 5 6
30
2
Supply Voltage (V) Fig. 4 Supply Current vs. Supply Voltage
3
4
5
Fig. 5
Supply Voltage (V) Supply Current vs. Supply Voltage
1.4
100
1.3
ILED_DUTY / ILEDMAX (%)
80
VIN=3.6V; L=10H CIN=1F, COUT=0.22F 3LEDs
RDSON ()
1.2
60
1.1
100Hz & 200Hz
40
1.0
500Hz
20
0.9
1KHz 2KHz
0 20 40
3KHz
60 80 100
0.8 2.5
3.0
Supply Voltage (V) Fig. 6 RDS-ON vs. Supply Voltage
3.5
4.0
4.5
5.0
5.5
6.0
0
SHDN PIN PWM Duty (%)
Fig. 7
Dimming Control by Shutdown PIN
4
AIC1647
TYPICAL PERFORMANCE CHARACTERISTICS
90 90
(Continued)
85
VIN=4.2V VIN=3.0V
VIN=4.2V
85
Efficiency (%)
Efficiency (%)
80
80
VIN=3.6V
75
75
VIN=3.6V VIN=3.0V 4 LEDs, 10H L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
0 5 10 15 20
70 65
3 LEDs, 10H L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
70
65
60 0
60
LED Current (mA) Fig. 8 3 LEDs Efficiency vs. LED Current
5
10
15
20
Fig. 9
LED Current (mA) 4 LEDs Efficiency vs. LED Current
85
80
VIN=4.2V
80 75
VIN=4.2V
Efficiency (%)
Efficiency (%)
75
VIN=3.6V VIN=3.0V
VIN=3.6V
70
70
5 LEDs, 10H L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
0 5 10 15 20
VIN=3.0V 6 LEDs, 10H
65
65
L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
60
60
LED Current (mA) Fig. 10 5 LEDs Efficiency vs. LED Current
0
Fig. 11
LED Current (mA) 6 LEDs Efficiency vs. LED Current
5
10
15
90
80
VIN=4.2V
85 75
6 LEDs, 6.8H L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
VIN=4.2V
Efficiency (%)
80 75 70 65 60
Efficiency (%)
VIN=3.0V
VIN=3.6V
70
VIN=3.6V
3 LEDs, 6.8H L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
0
65
VIN=3.0V
LED Current (mA) Fig. 12 3 LEDs Efficiency vs. LED Current
5
10
15
20
60
0
Fig. 13
LED Current (mA) 6 LEDs Efficiency vs. LED Current
5
10
15
5
AIC1647
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
VSHDN, 2V/div VSHDN, 2V/div VOUT, 2V/div
IINDUCTOR, 100mA/div
IINDUCTOR, 100mA/div
VOUT, 20V/div
VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=20mA
VIN=3.6V; 6 LEDs; L1=10F; COUT=0.22F; ILED=10mA
Fig. 14
Start-Up from Shutdown
Fig. 15
Start-Up from Shutdown
11.0
VOUT, 100mV/div
10.5
Output Voltage (V)
10.0 9.5 9.0 8.5 8.0 7.5 7.0 -40 -20
IINDUCTOR, 100mA/div
3 LEDs ILED=20mA 6 Samples' Temperature Data
0 20 40 60 80 100
VSW , 10V/div
VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=10mA
Fig. 16
Operation Wave Form
Temperature (C) Fig. 17 Output voltage vs. temperature
25
LED Current (mA)
20
15
VIN=4.2V
10 V =3.6V IN 5
VIN=3.3V VIN=2.5V
4 LEDs
-20 0 20 40 60 80 100
0 -80
Temperature (C) Fig. 18 LED Current vs. Temperature
-60
-40
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AIC1647
BLOCK DIAGRAM
95mV VREF SHDN PWM/PFM Control SW
+
VIN
+
Error AMP. PWM Comparator Slope -
FB
RC CC
Control Logic
Driver
M1
Internal Soft Start
1.2MHz Compensation Oscillator Current AMP
+ -
RS GND
PIN DESCRIPTIONS
PIN 1: SW - Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. - Ground Pin. Tie directly to local ground plane. - Feedback Pin. Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB = 95mV/ILED PIN 4: SHDN - Shutdown pin. Tie to higher than 1.5V to enable device, 0.3V or less to disable device. PIN 5: VIN - Power input pin. Bypass VIN to GND with a capacitor sitting as close to VIN as possible.
PIN 2: GND PIN 3: FB
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AIC1647
APPLICATION INFORMATION
Inductor Selection
A 10H inductor is recommended for most AIC1647 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance).
Open-Circuit Protection
In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the feedback voltage will be zero. AIC1647 will then switch to a high duty cycle resulting in a high output voltage, which may cause SW pin voltage to exceed its maximum 33V rating. A zener diode can be used at the output to limit the voltage on SW pin (Figure 1). The zener voltage should be larger than the maximum forward voltage of the LED string. The current rating of the zener should be larger than 0.1mA.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AIC1647 applications. X5R and X7R types are recommended because they retain their capacitance over wider ranges of voltage and temperature than other types, such as Y5V or Z5U. 1F input capacitor with 1F output capacitor are sufficient for most AIC1647 applications.
Dimming Control
There are three different ways of dimming control circuits as follows: 1. Using a PWM Signal PWM brightness control provides the widest dimming range by pulsing the LEDs on and off at full and zero current, respectively. The change of average LED current depends on the duty cycle of the PWM signal. Typically, a 0.1kHz to 1kHz PWM signal is used. Two applications of PWM dimming with AIC1647 are shown in Figure 19 and Figure 20. One, as Figure 19, uses PWM signal to drive SHDN pin directly for dimming control. The other, as Figure 20, employs PWM signal going through a resistor to drive FB pin. If the SHDN pin is used, the increase of duty cycle results in LED brightness enhancement. If the FB pin is used, on the contrary, the increase of duty cycle will decrease its brightness. In this application, LEDs are dimmed by FB pin and turned off completely by SHDN . 2. Using a DC Voltage For some applications, the preferred method of a dimming control uses a variable DC voltage to adjust LED current. The dimming control using a DC voltage is shown in Figure 21. Cautiously selecting R1 and R2 is essential so that the current from the variable DC source is much smaller than the LED current and much larger
Diode Selection
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC1647 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of AIC1647. An Schottky diode rated at 100mA to 200mA is sufficient for most AIC1647 applications.
LED Current Control
LED current is controlled by feedback resistor (RFB in Fig. 1). The feedback reference voltage is 95mV. The LED current is 95mV/ RFB. In order to have accurate LED current, precision resistors are preferred (1% recommended). The formula for RFB selection is shown below. RFB = 95mV/ILED
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AIC1647
than the FB pin bias current. With a VDC ranging from 0V to 5V, the selection of resistors in Figure 21 results in dimming control of LED current from 20mA to 0mA, respectively. 3. Using a Filtered PWM Signal Filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. The circuit is shown in Figure 22.
D1 RB512S-30 C2 SW D2
BZV55-B12 11.8V~12.2V
L1 VIN C1 1F PWM 10H VIN SHDN GND FB AIC1647
1F
20mA R1 1K RFB 4.7
Fig. 19 Dimming Control Using a PWM Signal with Open-Circuit Protection
L1 VIN C1 1F 10H VIN SHDN GND FB PWM AIC1647 SW
D1
RB512S-30 C2 D2 1F
BZV55-B12 11.8V~12.2V
20mA R1 1K RFB 4.7
R2 51K
Fig. 20 Dimming Control Using a PWM Signal
9
AIC1647
L1 VIN C1 1F 10H VIN SHDN GND FB 0~5VDC R2 51K R1 1K RFB 4.7 AIC1647 SW D2
BZV55-B12 11.8V~12.2V
D1
RB512S-30 C2 1F
20mA
Fig. 21 Dimming Control Using a DC Voltage
L1 VIN C1 1F 10H VIN SHDN GND FB AIC1647 R3 PWM 5.1K SW
D1
RB512S-30 C2 D2 1F
BZV55-B12 11.8V~12.2V
20mA R1 1K RFB 4.7
R2 51K
C3 0.1F
Fig. 22 Dimming Control Using a Filter PWM Signal
APPLICATION EXAMPLE
VIN C1 1F L 10H VIN SHDN GND FB AIC1647 20mA R2 1K RFB R1 SW
RB521S-30
D1 C2 1F
4.7
4.7
Fig. 23 Six white LEDs application in Li-Ion Battery
10
AIC1647
PHYSICAL DIMENSIONS (unit: mm)
SOT-23-5
D
S Y M B O L
SOT-25 MILLIMETERS 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 8 0.60 MAX. 1.45 0.15 1.30 0.50 0.22 3.00 3.00 1.70
A
E1
A1 A2 b
E
A
A
e e1
SEE VIEW B
c D E
b A2
WITH PLATING
E1 e
A
c
e1
BASE METAL SECTION A-A
L L1
A1
0.25 L L1 VIEW B
GAUGE PLANE SEATING PLANE
Note:
Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
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