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AIC1896
1.4MHz SOT23 Current-Mode Step-Up DC/DC Converter
FEATURES
Fixed Frequency 1.4MHz Current-Mode PWM Operation. Adjustable Output Voltage up to 30V. Guaranteed 13V/ 200mA Output with 5V Input. 2.5V to 10V Input Range. Maximum 0.1A Shutdown Current. Programmable Soft-Start. Tiny Inductor and Capacitors are allowed. Space-Saving SOT-23-6 Package.
DESCRIPTION
AIC1896 is a current-mode pulse-width modulation (PWM), step-up DC/DC Converter. The built-in high voltage N-channel MOSFET allows AIC1896 for step-up applications with up to 30V output voltage, as well as for Single Ended Primary Inductance Converter (SEPIC) and other low-side switching DC/DC converter. The high switching frequency (1.4MHz) allows the use of small external components. The Soft-Start function is programmable with an external capacitor, which sets the input current ramp rate. The AIC1896 is available in a space-saving SOT-23-6 package.
APPLICATIONS
White LED Backlight. OLED Driver.
TYPICAL APPLICATION CIRCUIT
VIN 3.3V or 4.2V C1 4.7F AIC1896
6
L
D1
CH521S-30
C3 1F
86 84 82
ZD1
BZV55-B12 11.8V~12.2V
Efficiency (%)
80 78 76 74 72 70 68 2 4 6 8
IN
LX
1 3
VIN=4.2V VIN=3.3V
OFF ON
4
SHDN FB SS GND
5 2
R2 1K ILED R1
C2 0.033F
L: GTSK-51-150M (15H) L: GTSK-51-100M (10H)
10 12 14 16 18 20
LED Current (mA)
Fig. 1 Li-Ion Powered Driver for three white LEDs
Analog Integrations Corporation
4F, 9 Industry E. 9th Rd, Science-Based Industrial Park, Hsinchu, Taiwan TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw
DS-1896-01
041103
1
AIC1896
VIN 3.6V or 4.2V C1 4.7F
L
D1
CH521S-30
80
C3 1F
78 76 74 72 70 68 66 64 62 60 2 4 6 8
ZD1
BZV55-B24
AIC1896
6 OFF ON 4
23.5V~24.5V
Efficiency (%)
IN
LX
1 3
VIN=4.2V VIN=3.6V
SHDN FB SS GND
5 2
R2 1K R1 ILED
C2 0.033F
L: GTSK-51-150M (15H) L: GTSK-51-100M (10H)
10 12 14 16 18 20
LED Current (mA)
Fig. 2 Li-Ion Powered Driver for six white LEDs
ORDERING INFORMATION
AIC1896-CXXX PACKING TYPE TR: TAPE & REEL BG: BAG PACKAGE TYPE G: SOT-23-6 Example: AIC1896-CGTR in SOT-23-6 Package & Tape & Reel Packing Type PIN CONFIGURATION SOT-23-6 (CG) FRONT VIEW 1: LX 2: GND 3: FB 4: SHDN 5: SS 6: IN
6 5 4
1
2
3
SOT-23-6 Marking
Part No. Marking
AIC1896CG
1896
2
AIC1896
ABSOLUTE MAXIMUM RATINGS
LX to GND FB to GND IN, SHDN SS to GND LX Pin RMS Current Continuous Power Dissipation (TA = +70C) (Note 1) 6-Pin SOT23 (derate 9.1mW/C above +70C) Operating Temperature Range Junction Temperature Storage Temperature Range Lead Temperature (soldering, 10s) area and still air. 727mW -40C to +85C +150C -65C to +150C +300C -0.3V to +33V -0.3V to +6V -0.3V to +11V -0.3V to +6V 0.6A
Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper
3
AIC1896
ELECTRICAL CHARACTERISTICS
to 85C, Unless otherwise specified) PARAMETER
SYMBOL
(VIN=V SHDN =3V, FB=GND, SS=Open, TA=-40C
CONDITIONS
MIN
TYP
MAX UNITS
Input Supply Range Output Voltage Adjust Range VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current
ERROR AMPLIFIER
VIN VOUT UVLO VIN rising, 50mV hysteresis IIN VFB = 1.3V, not switching VFB = 1.0V, switching V SHDN = 0, TA = +25C V SHDN = 0 VFB IFB VFB = 1.24V 2.6V < VIN < 5.5V fOSC DC Io RDS(ON) ILX(OFF) VLX = 12V, TA = +25C VLX = 12V Refer to Fig. 18
2.5 2.2 0.1 1 0.01 0.01 1.205 1.23 21 0.05 1000 82 1400 86
10 30 0.2 5 0.5 10 1.255 80 0.20 1800
V V V mA A A V nA %/V KHz % A
Feedback Regulation Set Point FB Input Bias Current Line Regulation
OSCILLATOR
Frequency Maximum Duty Cycle
POWER SWITCH
Steady State Output Current On-Resistance Leakage Current
SOFT-START
1 0.1
1.4 1 10 100
A
Reset Switch Resistance Charge Current
CONTROL INPUT
VSS = 1.2V VIL VIH I SHDN V SHDN , VIN = 2.5V to 10V V SHDN , VIN = 2.5V to 10V V SHDN = 3V V SHDN = 0
1.5
4
7.0 0.3
A V V
Input Low Voltage Input High Voltage
SHDN Input Current
1.0 25 0.01 50 0.1
A
4
AIC1896
TYPICAL PERFORMANCE CHARACTERISTICS
1.50
1.50
Switching Frequency (MHz)
1.45
TA=25C Frequency (MHz)
VIN=3.6V
1.45
1.40
1.35
1.40
1.30
1.35
1.25
1.20 -40 -20 0 20 40 60 80 100
1.30
2
3
4
5
6
7
8
9
10
11
Temperature (C) Fig. 3 Switching Frequency vs. Temperature
1.7 1.6
Supply Voltage (V) Fig. 4 Frequency vs. Supply Voltage
5.50
VIN=3.6V Output Voltage (V)
2 3 4 5 6 7 8 9 10 11
1.5
5.25
RDS(ON) ()
1.4 1.3 1.2 1.1 1.0 0.9 0.8
5.00
4.75
4.50 1
Supply Voltage (V) Fig. 5 RDSON vs. Supply Voltage
12.5
2.4
Output Current (mA) Fig. 6 Load Regulation
10
100
VIN=3.6V Output Voltage (V)
Supply Current (mA)
12.0
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8
FB=1.0V SHDN=1.0V
11.5
11.0
10.5
0.6
1
10
100
Output Current (mA) Fig. 7 Load Regulation
2
3
4
5
6
7
8
9
10
11
Supply Voltage (V) Fig. 8 Load Regulation
5
AIC1896
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
90
90 85
VIN=4.2V VIN=2.7V VIN=2.5V VIN=3.6V VIN=3.3V
Supply Current (A)
85
Efficiency (%)
80
FB=1.3V SHDN=1.0V
80 75 70 65 60 0
75
70
VOUT=5.0V
65 2 3 4 5 6 7 8 9 10 11
100
200
300
400
500
600
Supply Voltage (V) Fig. 9 Non-Switching Current
Output Current (mA) Fig. 10 Efficiency vs. Output Current
90
VLX
85
VIN=5.0V VIN=4.2V
Efficiency (%)
80
VIN=3.6V
75 70
VOUT
VIN=3.3V VOUT=12V
ILX
65 60 0 50 100 150 200
Output Current (mA) Fig. 11 Efficiency vs. Output Current
Fig. 12 Operation Wave Form (VIN=3V;VOUT=5V;L1=10H;R1=36K;R2=12K; C3=39pF;IOUT=200mA)
6
AIC1896
TYPICAL PERFORMANCE CHARACTERISTICS
(Continued)
SHDN
VSW
VOUT
VOUT ILX
ILX
Fig. 13 Operation Wave Form (VIN=5V; VOUT=12V, L1=22H; R1=105K; R2=12K;C3=1nF;IOUT=200mA)
Fig. 14 Start-Up from Shutdown (VIN=3.3V ;VOUT=13V ;RLOAD=300)
VOUT
VOUT
ILX
ILX
Fig. 15 Load Step Response (VIN=3.3V; VOUT=5V; IOUT=5mA to 200mA)
Fig. 16 Load Step Response (VIN=5V ; VOUT=12V ; IOUT=5mA to 150mA)
7
AIC1896
TYPICAL PERFORMANCE CHARACTERISTICS
1.25 800
(Continued)
Maximum Output Current (mA)
700 600 500 VOUT=5V 400 300 200 100
VOUT=13V VOUT=9V VOUT=15V
Feedback Voltage (V)
1.24
1.23
1.22
1.21
VIN=3.6V
1.20 -50
-25
0
25
50
75
100
2
3
4
5
6
7
8
9
10
Temperature (C)
Supply Voltage (V)
Fig. 17 Feedback Pin Voltage
Fig. 18 Maximum Output current vs. Supply Voltage
L1 VIN 2.5V to 10V + C1 10F/16V
D1 VOUT SS14 + R1 C4 10F C5 1F
U1 AIC1896
6 4
C3
1 3
IN SHDN SS
5
LX FB GND
2
SHDN C2 0.033F
R2
Fig. 19. Test circuit of figure 9~18.
8
AIC1896
BLOCK DIAGRAM
V IN PW M/P F M C ontrol R4 R3 + FB Q1 1 Q2 8 R1 RC CC 1.4M H z O scillator x1 + x20 LX E rror A m p PW M C om parator
+ -
I9 S oft- Start 4A SS
C ontrol Logic
D river
SHDN
R2
S lope C om pensation C urrent A m p x 5
RS GND
PIN DESCRIPTIONS
PIN 1: LX Power Switching Connection. Connect LX to inductor and output rectifier. Keep the distance between the components as close to LX as possible. Ground. Feedback Input. Connect a resistive voltage-divider from the output to FB to set the output voltage.
SHDN with a slew rate of 0.1V/s or greater. Do not leave SHDN unconnected. SHDN draws up to 50A.
PIN 5: SS
-
PIN 2: GND PIN 3: FB -
Soft-Start Input. Connect a soft-start capacitor from SS to GND in order to soft-start the converter. Leave SS open to disable the soft-start function. Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a capacitor sitting as close to IN as possible.
PIN 6: IN
-
PIN 4: SHDN - Shutdown Input. Drive SHDN low to turn off the converter. To automatically start the converter, connect SHDN to IN. Drive
9
AIC1896
APPLICATION INFORMATION
Inductor Selection
A 15H inductor is recommended for most AIC1896 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.4MHz and low DCR (copper wire resistance). R1 = 1.23V/ILED (1) accurate LED current, precision resistors are preferred (1% recommended). The formula for R1 selection are shown below.
Open-Circuit Protection Capacitor Selection
The small size of ceramic capacitors makes them ideal for AIC1896 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. A 4.7F input capacitor and a 1F output capacitor are sufficient for most AIC1896 applications. 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. AIC1896 will then switch to a high duty cycle resulting in a high output voltage, which may cause SW pin voltage to exceed its maximum 30V rating. A zener diode can be used at the output to limit the voltage on SW pin (Fig. 20). 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.
Diode Selection
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC1896 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 1.4MHz switching frequency of AIC1896. A Schottky diode rated at 100mA to 200mA is sufficient for most AIC1896 applications.
Dimming Control
There are three different types 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 using the control signal. The LEDs operate at either zero or full current, The average LED current changes with the duty cycle of the PWM signal. Typically, a 1kHz to 10kHz PWM signal is used. PWM dimming with the AIC1896 can be accomplished two different ways (see Fig. 21). The
SHDN pin can be driven directly or a resistor can
be added to drive the FB pin. If the SHDN pin is used, increasing the duty cycle will increase the LED brightness. If the FB pin is used, increasing the duty cycle will decrease the brightness. Using this method, the LEDs are dimmed using FB and turned off completely using SHDN .
LED Current Control
LED current is controlled by feedback resistor (R1 in Fig. 1). The feedback reference is 1.23V. The LED current is 1.23V/R1. In order to have
10
AIC1896
2. Using a DC Voltage
For some applications, the preferred method of brightness control uses a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Fig. 22. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 should make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias
VIN 3V to 4.2V C1 4.7F U1
6 4
current. For VDC range from 0V to 5V, the selection of resistors in Fig. 22 gives dimming control of LED current from 20mA to 0mA.
3. Using a Filtered PWM Signal
The 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 Fig. 23.
L1 10H
D1 CH521S-30 ZD1
BZV55-B20
C3 1F
AIC1896 LX FB GND
5 2 1 3
19.6V~20.4V
IN SHDN SS
OFF
ON
R2 1K R1 62
IOUT=ILED=20mA
C2 0.033F
Fig. 20 White LED Driver with Open-Circuit Protection
AIC1896 IN PWM SHDN SS LX FB GND
ZD1 IN R2 1K R1 62 OFF ON
AIC1896 LX FB GND
ZD1
SHDN SS
R2 1K R1 R3 30K 62
C2 0.033F
C2 0.033F
PWM
(a) Fig. 21 Dimming Control Using a PWM Signal
(b)
11
AIC1896
AIC1896
AIC1896 IN SHDN OFF ON SS LX FB GND R3 C2 0.033F 3.3K R2 1K R1 68 20mA~0mA ZD1
ZD1
IN SHDN OFF ON SS
LX FB GND R3 3.3K R4 4K C1 0.1F R2 1K R1 68
C2 0.033F
VDC 0V~5V
PWM
Fig. 22 Dimming Control Using a DC Voltage
Fig. 23 Dimming Control Using a Filtered PWM Signal
APPLICATION EXAMPLES
VIN 3V to 4.2V C1 4.7F L1 10H
CH521S-30
D1 C3 1F
ZD1
BZV55-B24
U1 AIC1896
6
23.5V~24.5V 1 3
IN SHDN SS
5
LX FB GND
2
OFF ON
4
R2 1K IOUT=ILED=20mA R1 62 R3 62
C2 0.033F
Fig. 24 Li-Ion Powered Driver for eight White LEDs with Open-Circuit Protection
12
AIC1896
PHYSICAL DIMENSIONS
SOT-23-6 (unit: mm)
D C L HE
SYMBOL A A1 A2 b C
MIN 1.00 -- 0.70 0.35 0.10 2.70 1.60 2.60 0.37 1
MAX 1.30 0.10 0.90 0.50 0.25 3.10 2.00 3.00 -- 9
e
1
D E e
A2
A A1 b
1.90 (TYP)
H L
1
13

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