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AIC1841/2 High Efficiency 1.5X charge Pump For White LEDs Backlighting
FEATURES
1MHz Switching Frequency 2.7V to 5.5V Input Voltage Range Low Shutdown Current: 1A Regulated 20mA Full-Scale Output Current 32-Position Linear Scale with Digital Control High Accuracy Brightness Matching 33% Less Input Current Than Doubler Charge Pump No Inductors Required Build-in Soft-Start Current Limit and Over Temperature Protection 12-Pin (AIC1841) and 16-Pin (AIC1842) QFN Package
GENERAL DESCRIPTION
The AIC1841 and AIC1842 provide 4 and 6 LED current source outputs with regulated constant current for uniform intensity. The AIC1841/2 is the low noise, constant frequency charge pump DC/DC converter that uses 1.5X conversion to increase efficiency in white LED applications. The devices can be used to produce current levels up to 20mA for each output from a 2.7V to 5.5V input. Low external parts counts (two 1 F flying capacitors and two small bypass capacitors at VIN, and OUT) make the AIC1841/2 ideal for small, battery-powered applications. EN/SET interface is used to enable, disable and set the LED current for a 32 level logic scale LED brightness control. Built-in current limiting, with thermal shutdown provide protection to the
APPLICATIONS
Cellular Phones PDAs Digital Still Cameras Handheld Devices White LED Backlighting
AIC1841/2 against fault conditions. Automatic softstart circuitry prevents excessive inrush current during start-up. 1MHz high switching frequency is enable to use tiny external components. The AIC1841 is available in a 12-pin thin QFN package, and the AIC1842 is available in a spacesaving 16-pin QFN package.
Analog Integrations Corporation
3A1, No.1 Li-Hsin Rd. I, Science Park, Hsinchu 300, Taiwan TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw
DS-1842P-02 041707
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AIC1841/2
TYPICAL APPLICATION CIRCUIT
VIN 2.7V~5.5V
4 CFLY1 1uF 5 10
C1+ C1VIN OUT EN/SET GND AIC1841
C2+ C2D1 D2 D3 D4
7 8 12 1 2 3
CFLY2 1uF LED1 LED2 LED3 LED4
Cin 1uF
6 Cout 1uF 11 9
VIN 2.7V~5.5V
6 CFLY1 1uF 7 14
C1+ C1VIN OUT EN/SET GND NC NC AIC1842
C2+ C2D1 D2 D3 D4 D5 D6
10 11 16 1 2 3 4 5
C FLY2 1uF LED1 LED2 LED3 LED4 LED5 LED6
Cin 1uF
9 Cout 1uF 15 12 8 13
2
AIC1841/2
ORDERING INFORMATION
AIC1841/2XXXXX PACKING TYPE TR: TAPE & REEL BG: BAG PACKAGE TYPE HD: QFN-12 (3x3x0.9mm) HF: QFN-16 (3x3x0.9mm) HJ: QFN-16 (4x4x0.9mm) G: Green Package PIN CONFIGURATION
EN/SET
QFN-12 (only for AIC1841) TOP VIEW
VIN 9 GND (GND) 8 C27 C2+ 4 C1+ 5 C1EN/SET 6 OUT VIN 7 C1NC 12 GND (GND) 11 C210 C2+ 9 OUT 5 D6 6 C1+ 8 NC D1 D2 1 D3 2 D4 3 D2 1 D3 2 D4 3 D5 4
12 11 10
Example: AIC1841GHDTR in Green QFN-12 (3x3x0.9mm) Package and Tape & Reel Packing Type AIC1842GHFTR in Green QFN-16 (3x3x0.9mm) Package and Tape & Reel Packing Type
QFN-16 (only for AIC1842) TOP VIEW
D1
16 15 14 13
ABSOLUTE MAXIMUM RATINGS
VIN, VOUT, EN/SET to GND ...........................................................................................................6.0V Thermal Resistance JA (C/W) ................................................................................................. 48C/W Operating Temperature Range ........................................................................................ -40C to 85C Junction Temperature ...................................................................................................................125C Storage Temperature Range ......................................................................................... -65C to 150C Lead Temperature (Soldering 10s) ...............................................................................................260C Thermal Resistance Junction to Ambient, RJA (Assume no ambient airflow, no heatsink) QFN-12/16 (3x3X0.9mm) QFN-16 (4x4X0.9mm) Thermal Resistance Junction to Case, RJC QFN-12/16 (3x3X0.9mm) QFN-16 (4x4X0.9mm) 8C /W 8C /W 48C /W 43C /W
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
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AIC1841/2
ELECTRICAL CHARACTERISTICS
(VIN=3.6V, EN/SET = IN, CIN = C1 = C2 = COUT = 1F, TA=25C, Unless otherwise specified.) (Note1) PARAMETER
Operating Voltage Undervoltage-Lockout Threshold Undervoltage-Lockout Hysteresis Operating Current Shutdown Current Output Current Output Current Line Regulation LED to LED Current Matching (Note2) Soft-Start Time Switching Frequency Enable Threshold Low Enable Threshold High EN/SET Low Time Minimum EN/SET High Time EN/SET Off Timeout EN/SET Input Leakage Thermal Shutdown Threshold Thermal Shutdown Hysteresis VIN = 5.5V -1 150 25 VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V 1.4 0.3 50 300 500 1 75 0.75 3.0V VIN 5.5V, AIC1841 3.2V VIN 5.5V, AIC1842 AIC1841 AIC1842 3 4 400 1 1.25 0.5 7 % 8 s MHz V V s ns s A C C Active, No Load Current EN = 0 18 -2 20 VIN falling
TEST CONDITIONS
MIN.
2.7 2.25
TYP.
MAX.
5.5
UNITS
V V mV
2.45 120 1
2.60
2 1 22 2
mA A mA %/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). Note 2: Current matching define: (ILED1-ILED2) / (ILED1+ILED2), between any two outputs
4
AIC1841/2
TYPICAL PERFORMANCE CHARACTERISTICS
VEN Vo VD IIN
Vin=3.6V
VEN Vo VD
IIN
Vin=3.6V
Fig1: Enable Transient Response
Fig2: Shutdown Timeout
VIN Vo
VIN Vo
VD
VD
Fig3: 80mA load at Vin=3.0V
Fig4: 100mA load at Vin=3.0V
VIN Vo
VIN Vo
VD
VD
Fig5: 80mA load at Vin=3.6V
Fig6: 120mA load at Vin=3.6V
5
AIC1841/2
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
V IN Vo V IN Vo
VD
VD
Fig7: 80mA load at Vin=4.2V
Fig8: 120mA load at Vin=4.2V
EN/SET
EN/SET
IDIODE
IDIODE
Fig9: EN/SET Pin 10kHz Clock Transient
Fig10: EN/SET Pin 100kHz Clock Transient
1.50
EN/SET
Quiescent Current (mA)
1.25
IDIODE
1.00
0.75
0.50 3.0 3.5 4.0 4.5 5.0 5.5
Fig11: EN/SET Pin 1MHz Clock Transient
Input Voltage (V)
Fig12: Quiescent vs. Supply Voltage
6
AIC1841/2
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
1.5
1.250
Quiescent Current (mA)
Quiescent Current (mA)
1.4
1.225
1.3
1.200
1.2
T = 25 OC T = -40 C
O
1.175
1.1
T = 85 OC
1.150
1.0 0.9 3.0 3.5 4.0 4.5 5.0 5.5
1.125
1.100 -40
-20
0
20
40
o
60
80
100
Input Voltage (V) Fig13: Quiescent Current vs. Input Voltage
0.5
1.10
Temperature ( C) Fig14: Quiescent Current vs. Temperature
Shutdown Current (A)
0.4
Normalized LED current
0
1.05
0.3
1.00
0.2
0.1
0.95
0.0 -40
-20
20
40
o
60
80
100
0.90 -40
-20
0
20
40
o
60
80
100
Temperature ( C) Fig15: Shutdown Current vs. Temperature
1.20
1.20
Temperature ( o C) Fig16: Normalized LED Current vs. Temperature
1.15
1.15
Frequency (MHz)
1.10
T = 25 OC T = -40 OC T = 85 OC
Frequency (MHz)
1.10
1.05
1.05
1.00
1.00
0.95
0.95
0.90
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Fig17: Frequency vs. Input Voltage
0.90 -40
-20
0
20
40
o
60
80
100
Temperature ( C) Fig18: Frequency vs. Temperature
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AIC1841/2
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
120
Output Current (mA)
Output Current (mA)
100
Vin > 3.4V Vin = 3.2V Vin = 3.0V
80 70 60 50 40 30 20 10 0
Vin > 3.2V Vin = 3.0V Vin = 2.7V
80
60
Vin = 2.7V
40
20
0
0
4
8
12
16
20
24
28
32
0
4
8
12
16
20
24
28
32
Digital Code Fig19: 32 Levels Current Setting with 6 LEDs
100
90
Digital Code Fig20: 32 Levels Current Setting with 4 LEDs
Vin = 3.0V
90
2 LEDs (40mA)
Vin = 3.6V Vin = 3.9V
85
Efficiency (%)
Efficiency (%)
Vin = 2.7V Vin = 3.3V
80
80
75
VF = 3.75V
Vin = 4.2V
70
70
Vin = 5.0V
60
65
VF = 3.45V
3.2 3.4 3.6
VF = 3.6V
0
20
40
60
80
100
120
60 3.0
3.8
4.0
4.2
LED Current (mA)
Fig21: Efficiency vs. Supply Current
90 90
Supply Voltage (V) Fig22: Efficiency vs. Supply Voltage
4 LEDs (80mA)
85 85
6 LEDs (120mA)
Efficiency (%)
75
VF = 3.75V
Efficiency (%)
80
80
75
VF = 3.75V
70
70
65
VF = 3.45V
VF = 3.6V
65
VF = 3.45V
VF = 3.6V
60 3.0
3.2
3.4
3.6
3.8
4.0
4.2
60 3.0
3.2
3.4
3.6
3.8
4.0
4.2
Supply Voltage (V) Fig23: Efficiency vs. Supply Current
Supply Voltage (V) Fig24: Efficiency vs. Supply Voltage
8
AIC1841/2
BLOCK DIAGRAM
C1
1uF
C2
1uF
C1P
C1N
C2P
C2N
OSC
1.5X CHARGE PUMP
VOUT COUT
1uF
VIN CIN
1uF
UVLO
SS
OTP
OCP
OVP EN/SET EN & BIAS REFERENCE
CURRENT CONTROLLER
COUNTER
ILED1
ILED2
ILED3
ILED4
ILED5
ILED6
GND
D1
D2
D3
D4
D5
D6
LED1
LED2
LED3
LED4
LED5
LED6
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AIC1841/2
PIN DESCRIPTIONS
D1: D2: D3: D4: D5: D6: Current source output. Current source output. Current source output. Current source output. Current source output. (AIC1842 only) Current source output. (AIC1842 only) OUT: Charge pump output. For the best performance, OUT should bypass a 1F (min.) low ESR ceramic capacitor with the shortest distance to ground. GND: Ground. Connect GND as close as possible to system ground and to the ground of the input bypass capacitor. VIN: Input supply voltage. Bypass a 1uF (min.) low ESR ceramic capacitor to GND as close to device as possible. The input voltage range is 2.7V to 5.5V. EN/SET: Enable and current set pin.
C1+: Flying capacitor 1 positive terminal. C1-: Flying capacitor 1 negative terminal. C2+: Flying capacitor 2 positive terminal. C2-: NC: Flying capacitor 2 negative terminal. No connect. (AIC1842 only)
APPLICATION INFORMATION
Operation The AIC1841/2 is a high efficiency 1.5X charge pumps intended for WLED backlighting. This kind of converter uses capacitors to store and transfer energy. Since the capacitors can't change to the voltage level abruptly, the voltage ratio of VOUT to VIN is limited. Capacitive voltage conversion is obtained by switching a capacitor periodically. Refer to Fig. 25, during the "on" state of internal clock, Q1, Q4 and Q7 are closed, which charges CFLY1 and CFLY2 to 1/2VIN level. During the "off" state, Q2, Q3, Q5 and Q6 are closed. The output voltage is VIN plus VCFLY, that is, 1.5VIN.
VIN CIN Q1 Q3 Q6 Q2 CFLY1 Q4 Q5 CFLY2 Q7 VOUT COUT
The AIC1841/2 only requires one 1F ceramic capacitor for CIN, one 1F ceramic capacitor for COUT and two 1uF ceramic capacitors for the charge pump flying capacitors. Efficiency The efficiency of AIC1841/2 for ideal 1.5X charge pump can be simply defined as: xI P V V xI V = OUT = OUT OUT = OUT OUT = OUT PIN VIN x IIN VIN x 1.5I OUT 1.5VIN The actual efficiency will decrease as the result from internal switching loss. WLED Current Level Setting The AIC1841/2 D1 to D4/D6 are constant current outputs which source up to 20mA respectively to drive four or six WLEDs. The LED current is set via serial interface by the EN/SET pin, which is based on a digital sacle. The interface records rising edges of the EN/SET pin, and counts them into 32 current level settings where each code is 0.625mA greater than previous code. Code 1 is
Fig. 25 The circuit of 1.5X charge pump
10
AIC1841/2
the lowest current scale, 0.625mA, and Code 32 is full scale, 20mA. The LED current appears linear with each increasing code. The first rising edge enables the device and sets the LED output current to the lowest setting level, 0.625mA. After
20 18 16 14 12
32nd clock, the LED output returns to state 1. The EN/SET pin has to remain high to keep the LED output current to programmed level when the final clock is input.
ILED(mA)
10 8 6 4 2 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
Digital Code
Code 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
WLED Current 0.625 1.250 1.875 2.500 3.125 3.750 4.375 5.000 5.625 6.250 6.875 7.500 8.125 8.750 9.375 10.000
Code 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
WLED Current 10.625 11.250 11.875 12.500 13.125 13.750 14.375 15.000 15.625 16.250 16.875 17.500 18.125 18.750 19.375 20.000
EN/SET Interface The EN/SET timing is as the diagram shown below. The first rising edge enables the device and sets the LED output current to the lowest setting level. The AIC1841/2 reaches full capaciity after typically 400us soft start time. During the soft start period, multiple clock pulses may be inserted, they will be missed cause the counter of EN/SET interface will work after soft start time. The 2
nd
pulse should be later than 1 pulse for a soft start time to maintain a correct LED output current level. The counter can be clocked up to 1MHz, so the intermediate scales are not visible.The EN/SET has to hold high to keep the output LED current to programmed level when the final clock is input. When the EN/SET keeps a low for the tSHDN timeout period or longer, the AIC1841/2 is shutdown.
st
EN
t (LO) 0.3us to 75us 10 11
t (HI) >50ns 12
. . . .
29
30
31
32 t (SHDN) 300us
t (SOFT-START) 400us I(LED) SHDN 1BIT 2 3
4
5
6
7
8
9
1
2
3
4 SHDN
Current Setting Diagram
11
AIC1841/2
Open-Circuit Protection In any cases of open output circuit, the LEDs are disconnected from the circuit or the LEDs are failed, etc., the output voltage will limit approximately to 5V. Thermal Protection When the temperature of device exceeds To reduce noise and ripple, low ESR ceramic capacitor is recommended for CIN and COUT. The value of COUT determines the amount of output ripple voltage. An output capacitor with larger value results in smaller ripple. CFLY is critical for the charge pump which affects turn on time. The larger CFLY is, the higher output current obtains. However, large CIN and COUT are required when large CFLY applies. The ratio of CIN (as well as COUT) to CFLY should be approximately 1:1 to 10:1.
approximately 150C, the thermal protection will shut the switching down and the temperature will reduce afterwards. Once the temperature drops below approximately 125C, the charge pump switching circuit will re-start. Even though all six outputs shorted to ground at maximum 120mA, the die temperature will not increase sufficiently to enable the thermal protection resulting from its low thermal resistance.
Layout Considerations
Due to the switching frequency and high transient current of AIC1841/2, careful consideration of PCB layout is necessary. The CIN should be connected as close to the IC as possible. The ground of CIN and COUT should be placed as close as possible. To achieve the best performance of AIC1841/2, minimize the distance between every two components and also minimize every connection length with a maximum trace width. Make sure each device connects to immediate ground plane.
Capacitor Selection
Four external capacitors, CIN, COUT, CFLY1, and CFLY2, determine AIC1841/2 performances. Optimum performance can be obtained by using low ESR ceramic capacitors. A 1uF ceramic capacitor for all four capacitors is recommended for genernal application.
Application Example
. When using the AIC1841/2 to drive fewer than four/six LEDs, keep current output float. The
D1 D2 D3 D4 D5 D6 C1+ CFLY1 1uF C1AIC1842 EN/SET VIN NC GND C2C2+ OUT NC Cout 1uF CFLY2 1uF EN/SET Vbattery Cin 1uF
corresponding LED current still enables.
12
AIC1841/2
.Any combination of output may be connected in parallel to deliver a single power output to drive a LED module. The maximum output current is the sum of parallel-connected
LED Module
current source. This feature is useful to drive pre-wire LED backlight modules, which is connected in parallel structure circuit.
U1 D1 D2 D3 D4 D5 D6 C1+ CFLY1 1uF C1AIC1842 EN/SET VIN NC GND C2C2+ OUT NC Cout 1uF CFLY2 1uF EN/SET Vbattery Cin 1uF
Enable
Display backlight
U1 D1 D2 D3 EN/SET VIN NC GND C2C2+ OUT NC Cout 1uF CFLY2 1uF EN/SET Vbattery Cin 1uF
Enable
Keypad backlight
D4 D5 D6
CFLY1 1uF
C1+ C1AIC1842
13
AIC1841/2
PHYSICAL DIMENSIONS (unit: mm)
QFN 12L - 3x3x0.9-0.5mm
D
12 11
D2 11
12
1 2
1
INDEX AREA (D/2*E/2)
e
b
A1
A3
A
S Y M B O L
QFN 12L-3x3x0.9-0.5mm MILLIMETERS MIN. 0.80 0.00 0.20 REF 0.18 2.90 1.50 2.90 1.50 0.45 0.35 0 0.30 3.10 1.80 3.10 1.80 0.55 0.45 12 MAX. 1.00 0.05
A A1 A3
Note : 1. Refer to JEDEC MO-220 VEED-3. 2. All dimensions are in millimeters, is in degrees.
b D D2 E E2 e L
E2
2
E
L
14
AIC1841/2
QFN 16L - 3x3x0.9-0.65mm
D D2 L
1 2 1
INDEX AREA (D/2*E/2)
e
b
A1
A3
A
S Y M B O L
QFN 16L-3x3x0.9-0.5mm MILLIMETERS MIN. 0.80 0.00 0.20 REF 0.18 2.90 1.05 2.90 1.05 0.50 BSC 0.30 0 0.55 14 0.30 3.10 1.80 3.10 1.80 MAX. 1.00 0.05
A A1 A3
Note: 1. Refer to JEDEC MO-220 VEED-4,6,7 2. All dimensions are in millimeters, is in degrees.
b D D2 E E2 e L
E2
2
E
15
AIC1841/2
QFN 16L - 4x4x0.9-0.65mm
D D2 L
1 2 1
INDEX AREA (D/2*E/2)
e
b
A1
A3
A
S Y M B O L
QFN 16L-4x4x0.9-0.65mm MILLIMETERS MIN. 0.80 0.00 0.20 REF 0.25 3.90 2.20 3.90 2.20 0.65 BSC 0.30 0 0.65 14 0.35 4.10 2.80 4.10 2.80 MAX. 1.00 0.05
A A1 A3
Note: 1. Refer to JEDEC MO-220 VGGC-2,3,4 2. All dimensions are in millimeters, is in degrees.
b D D2 E E2 e L
E2
2
E
16
AIC1841/2
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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