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AIC1648
Built-in OVP White LED Step-Up Converter
FEATURES
Built-In Open Circuit Protection Over Voltage Protection Efficiency Up to 84% at VIN=4.2V, 3LEDs, ILED=20mA 1.2MHz Fixed Switching Frequency Drives Up to 5LEDs in series Low Supply Current: 70A Matches LED Current Requires Tiny Inductor and Capacitors Tiny SOT-23-6 Package
DESCRIPTION
AIC1648 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 LEDs provides identical LED currents resulting in uniform brightness. This configuration eliminates the need of ballast resistors. The built-in open load protection prevents the damage resulting from an open circuit condition. Low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency.
APPLICATIONS
Cellular Phones PDAs DSCs Handheld Devices White LED Display Backlighting
AIC1648 is a step-up PWM converter, which includes an internal N-channel MOSFET switch for high efficiency. The high switching frequency, 1.2MHz, allows the use of tiny external components. AIC1648 is available in a space-saving, 6-lead SOT-23-6 package.
TYPICAL APPLICATION CIRCUIT
3.3~4.2V C1 1F L 6.8H VIN SW D1 C2 1F
90
VIN=4.2V
85
Efficiency (%)
80 75 70
SHDN OVP GND FB RFB 4.7 20mA
VIN=3.0V
VIN=3.6V
AIC1648 L1: 976AS-6R8M/D321F, 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 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-1648P-03 010405
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AIC1648
ORDERING INFORMATION
AIC1648XXXX PACKING TYPE TR: TAPE & REEL BG: BAG PACKAGE TYPE G: SOT-23-6 C: COMMERCIAL P: LEAD FREE COMMERCIAL Example: AIC1648CGTR in SOT-23-6 Package & Tape & Reel Packing Type
1 2 3
ORDER NUMBER AIC1648CG&PG (SOT-23-6)
PIN CONFIGURATION
FRONT VIEW
VIN OVP SHDN
6 5 4
SW GND FB
MARKING Part No. AIC1648
CG 1648
PG 1648P
ABSOLUTE MAXIMUM RATINGS
Input Voltage (VIN) SW Voltage FB Voltage
SHDN Voltage
6V 33V 6V 6V 34V -40C to 85C 125C -65C to 150C 260C
OVP Voltage 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 SW OVP FB RFB 4.7 ILED D1 C2 0.22F
AIC1648 L1: 976AS-100M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ224KG, TAIYO YUDEN
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AIC1648
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
OVER VOLTAGE PROTECTION OVP Input Resistance OVP Threshold ROVP VOVP 1V Hysteresis typical 0.6 22 1.2 27 1.8 32 M 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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AIC1648
TYPICAL PERFORMANCE CHARACTERISTICS
1.6
Switching Frequency (MHz)
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
50
100
150
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
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
3
4
5
6
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
20 40
3KHz
SHDN PIN PWM Duty (%)
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
00
Fig. 7
Dimming Control by Shutdown PIN
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AIC1648
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
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
5
10
15
20
85
90
VIN=4.2V
80 85
VIN=4.2V
Efficiency (%)
Efficiency (%)
80 75 70 65 60
75
VIN=3.6V VIN=3.0V
VIN=3.0V
VIN=3.6V
70
5 LEDs, 10H L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
0
3 LEDs, 6.8H L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1
0 5 10 15 20
65
60
LED Current (mA) Fig. 10 5 LEDs Efficiency vs. LED Current
5
10
15
20
LED Current (mA) Fig. 11 3 LEDs Efficiency vs. LED Current
VSHDN, 2V/div
VOUT, 100mV/div
VOUT, 2V/div
IINDUCTOR, 100mA/div
IINDUCTOR, 100mA/div
VSW , 10V/div
VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=20mA
Fig. 12
Start-Up from Shutdown
VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=10mA
Fig. 13
Operation Wave Form
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AIC1648
TYPICAL PERFORMANCE CHARACTERISTICS
11.0 10.5
25
(Continued)
Output Voltage (V)
10.0 9.5 9.0 8.5 8.0 7.5 7.0 -40 -20
LED Current (mA)
20
15
3 LEDs ILED=20mA 6 Samples' Temperature Data
0 20 40 60 80 100
VIN=4.2V
10 V =3.6V IN
VIN=3.3V
5
VIN=2.5V 4 LEDs
Temperature (C) Fig. 14 Output voltage vs. temperature
0 -80
Temperature (C) Fig. 15 LED Current vs. Temperature
-60
-40
-20
0
20
40
60
80
100
BLOCK DIAGRAM
Over Voltage Comparator 27V
+
PWM/PFM Control
SHDN
OVP
-
SW VIN
95mV VREF Control Logic
+
Driver
M1 *
Error AMP
PWM Comparator
+
FB
Slope Compensation
1.2MHz Oscillator
RC* CC
*
+ Current AMP. -
RS* GND
Internal Soft Start
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AIC1648
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 to obtain LED current according to the formula: RFB = 95mV/ILED PIN 6: VIN PIN 4: SHDN - Shutdown pin. Tie to higher than 1.5V to enable device, 0.3V or less to disable device. PIN 5: OVP - Overvoltage protection. When VOUT is greater than 27V, the internal MOSFET turns off. - Power input pin. Bypass VIN to GND with a capacitor sitting as close to VIN as possible.
PIN 2: GND PIN 3: FB
APPLICATION INFORMATION
Inductor Selection
A 10H inductor is recommended for most AIC1648 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). and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of AIC1648. An Schottky diode rated at 100mA to 200mA is sufficient for most AIC1648 applications.
LED Current Control
LED current is controlled by feedback resistor (RFB in Figure 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
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AIC1648 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 AIC1648 applications.
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. AIC1648 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. Connect builtin OVP (Over Voltage Protection) pin to output terminal to prevent the damage resulting from an open circuit condition.
Diode Selection
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC1648 applications. The forward voltage drop of an 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
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AIC1648
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 AIC1648 are shown in Figure 16 and Figure 17. One, as Figure 16, uses PWM signal to drive SHDN pin directly for dimming control. The other, as Figure 17, 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
D1 C2 1F
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 18. With a VDC ranging from 0V to 5V, the selection of resistors in Figure 18 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 19.
L VIN C1 1F PWM 10H VIN SW
RB521S-30
SHDN OVP GND FB RFB 4.7
AIC1648
Fig. 16 Dimming Control with a PWM Signal
L VIN C1 1F 10H VIN SW
RB521S-30
D1 C2 1F
SHDN OVP GND FB PWM R2 51K
AIC1648
R1 1K
RFB 4.7
Fig. 17 Dimming Control Using a PWM Signal
8
AIC1648
L VIN C1 1F 10H VIN SW
RB521S-30
D1 C2 1F
SHDN OVP GND FB VDC 0~5V AIC1648 R2 51K R1 1K RFB 4.7
Fig. 18 Dimming Control Using a DC Voltage
L VIN C1 1F 10H
RB521S-30
D1 C2 1F
VIN
SW
SHDN OVP GND FB AIC1648 R3 5.1K R1 1K R2 51K C3 0.1F RFB 4.7
PWM
Fig. 19 Dimming Control Using a Filter PWM Signal
APPLICATION EXAMPLE
3.0~4.2V C1 1F L 10H VIN SW
RB521S-30
D1 C2 1F
SHDN OVP GND FB AIC1648 RFB 4.7 R1 4.7 20mA
Fig. 20 Six White LEDs Application in Li-Ion Battery
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AIC1648
PHYSICAL DIMENSIONS (unit: mm)
SOT-23-6
D
S Y M B O L
SOT-26 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
E
A2 b c
A
A
e e1
SEE VIEW B
D E E1
b A2
WITH PLATING
e e1
A
c
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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