Anachip AP1521WA White led step-up converter Datasheet

AP1521
White LED Step-Up Converter
„ Features
„ General Description
- Inherently Matched LED Current
- Drives Up to Four LEDs from a 3.2V Supply
- Drives Up to Six LEDs from a 5V Supply
- High Efficiency: 84% Typical
- Fast 1MHz Switching Frequency
- 36V Rugged Bipolar Switch
- Low Profile SOT23-5 Pb-Free Packaging
The AP1521 is a step-up DC/DC converter
specifically designed to drive white LEDs with a
constant current. The device can drive two, three or
four LEDs in series from a Li-Ion cell. Series
connection of the LEDs provides identical LED
currents resulting in uniform brightness and
eliminates the need for ballast resistors. The
AP1521 switches at 1MHz that allows the use of
tiny external components. A low 300mV feedback
voltage minimizes power loss in the current setting
resistor for better efficiency.
„ Applications
- Cellular Phones
- PDAs, Hand-held Computers
- Digital Cameras
- MP3 Players
- GPS Receivers
„ Pin Descriptions
„ Pin Assignments
Top View
VIN
SHDN
SW VSS
FB
Name
Description
SW
Switch Pin. Connect inductor/diode
here. Minimize trace area at this pin
to reduce EMI.
VSS
GND pin
FB
Feedback Pin. Reference voltage is
310mV. Connect cathode of lowest
LED and resistor here. Calculate
resistor value according to the
formula: RFB = 310mV / ILED
SHDN
Shutdown Pin. Tie to 1.5V or higher
to enable the device;0.4V or less to
disable the device.
VIN
Input Supply Pin. Must be locally
bypassed.
SOT23-5L
„ Ordering Information
AP1521 X X
Package
Packing
W: SOT23-5L
Blank : Tube
A : Taping
This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of
this product. No rights under any patent accompany the sale of the product.
Rev. 0.1 Apr. 27, 2004
1/8
AP1521
White LED Step-Up Converter
„ Block Diagram
1 SW
Comparator
Driver
A2
+
-
A1
R
S
Q1
Q
RC
+
CC
FB 3
310mV
+
VREF
1.25V
Σ
-
VIN 5
RAMP
Generator
2 GND
Shutdown
SHDN 4
1MHz
Oscillator
„ Absolute Maximum Ratings
Symbol
Parameter
Rating
Unit
VIN
VIN Pin Voltage
10
V
VSW
SW Voltage
36
V
VFB
Feedback Pin Voltage
10
V
VSHDN
TJ
TLEAD
TOPR
SHDN Pin Voltage
10
Maximum Junction Temperature
125
o
C
300
o
C
-40 to +85
o
C
Lead Temperature
Operating Temperature Range
V
o
TSTG
Storage Temperature Range
-40 to +125
C
Caution The absolute maximum ratings are rated values exceeding which the product could suffer physical
damage. These values must therefore not be exceeded under any condition.
Anachip Corp.
www.anachip.com.tw
Rev. 0.1
2/8
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Electrical Characteristics (Ta=25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.)
Symbol
VIN
VIN
VFB
IFB
Parameter
Minimum Operation Voltage
Maximum Operation Voltage
Feedback Pin Voltage
Feedback Pin Bias Current
Conditions
-
Supply Current
VSHDN = 0V
Min.
2.5
-280
10
--
Typ.
--310
45
1.9
Max.
-10
340
100
2.5
Unit
V
V
mV
nA
mA
--
0.1
1.0
µA
FSW
Switching frequency
0.75
1.0
1.25
MHz
Duty
ISW
VSAT
PWM Maximum Duty Cycle
Switch Current Limit
Switch VSAT
Switch Leakage Current
SHDN Pin Voltage High
SHDN Pin Voltage Low
SHDN Pin Bias Current
85
---1.5
---
90
320
350
0.01
--65
---5
-0.4
--
%
mA
mV
µA
V
V
µA
VSHDN
VSHDN
ISHDN
ISW = 250mA
VSW = 5V
Enable
Disable
„ Typical Application Circuit
L1
22uH
D1
C2
0.22uF
C1
1uF
LED1
15mA
LED2
SW
Vin
LED3
Vss
R1
20ohm
FB
SHDN
ON OFF
C1, C2: X5R or X7R Dielectric
D1: Central Semiconductor CMDSH-3
L1: MURATA LQH3C-220 or Equivalent
Figure 1.
Anachip Corp.
www.anachip.com.tw
Rev. 0.1
3/8
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Applications Information
Capacitor Selection
The small size of ceramic capacitors makes them
ideal for AP1521 applications. X5R and X7R types
are recommended because they retain their
capacitance over wider voltage and temperature
ranges than other types such as Y5V or Z5U. A
1µF input capacitor and a 0.22µF output capacitor
are sufficient for most AP1521 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. The AP1521 will
then switch at a high duty cycle resulting in a high
output voltage, which may cause the SW pin
voltage to exceed its maximum 36V rating. A
zener diode can be used at the output to limit the
voltage on the SW pin (Figure 2). 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.
Inductor Selection
A 22µH inductor is recommended for most AP1521
applications.
Although small size and high
efficiency are major concerns, the inductor should
have low core losses at 1MHz and low DCR
(copper wire resistance).
L
22uH
V IN
D
COUT
0.22uF
C IN
1uF
Diode Selection
Schottky diodes, with their low forward voltage drop
and fast reverse recovery, are the ideal choices for
AP1521 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 1MHz switching frequency of the
AP1521. A Schottky diode rated at 100mA to
200mA is sufficient for most AP1521 applications.
VIN
SW
AP1521
SHDN
FB
R2
1k
R1
15Ω
GND
Figure 2. LED Driver with Open-Circuit Protection
Dimming Control
There are four different types of dimming control
circuits:
1. Using a PWM Signal to SHDN Pin
With the PWM signal applied to the SHDN pin,
the AP1521 is turned on or off by the PWM signal.
The LEDs operate at either zero or full current.
The average LED current increases proportionally
with the duty cycle of the PWM signal. A 0% duty
cycle will turn off the AP1521 and corresponds to
zero LED current. A 100% duty cycle corresponds
to full current. The typical frequency range of the
PWM signal is 1kHz to 10kHz. The magnitude of
the PWM signal should be higher than the minimum
LED Current Control
The LED current is controlled by the feedback
resistor (R1 in Figure 1). The feedback reference
is 310mV. The LED current is 310mV/R1. In
order to have accurate LED current, precision
resistors are preferred (1% is recommended). The
formula and table for R1 selection are shown below.
R1 = 310mV/ILED
(See Table 1)
SHDN voltage.
Table 1. R1 Resistor Value Selection
ILED (mA)
R1 (Ω)
5
62
10
31
12
25.8
15
20.7
20
15.5
AP1521
SHDN
PWM
Anachip Corp.
www.anachip.com.tw
Rev. 0.1
4/8
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Applications Information (Continued)
2. Using a DC Voltage
For some applications, the preferred method of
brightness control is a variable DC voltage to adjust
the LED current. The dimming control using a DC
voltage is shown in Figure 3. 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
will make the current from the variable DC source
much smaller than the LED current and much larger
than the FB pin bias current. For VDC range from
0V to 2V, the selection of resistors in Figure 3 gives
dimming control of LED current from 0mA to 15mA.
4. Using a Logic Signal
For applications that need to adjust the LED current
in discrete steps, a logic signal can be used as
shown in Figure 5. R1 sets the minimum LED
current (when the NMOS is off). RSET sets how
much the LED current increases when the NMOS is
turned on.
Start-up and Inrush Current
To achieve minimum start-up delay, no internal
soft-start circuit is included in AP1521. When first
turned on without an external soft-start circuit,
inrush current is about 200mA. If soft-start is
desired, the recommended circuit and the
waveforms are shown in Figure 6.
If both
soft-start and dimming are used, a 10kHz PWM
signal on SHDN is not recommended. Use a lower
frequency or implement dimming through the FB pin
as shown in Figures 3, 4 or 5.
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 Figure 4.
VDC
AP1521
AP1521
FB
FB
R3
90k
R2
5k
RSET
Logic
Signal
R1
15Ω
Figure 3. Dimming Control Using a DC Voltage
Figure 5. Dimming Control Using a Logic Signal
D1
2.2nF
AP1521
FB
PWM
10k
R3
90k
0.1uF
R1
AP1521
FB
R2
5k
D2
R2
1k
5k
R1
15Ω
COUT
R1
15Ω
D2:MMBT
Figure 6. Recommended Soft-Startup Circuit
Figure 4. Dimming Control Using a Filtered PWM
Signal
Anachip Corp.
www.anachip.com.tw
Rev. 0.1
5/8
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Typical Performance Characteristics
Li-lon to Two White LEDs
D
CIN
1uF
COUT
1uF
VDC
Dimming
VIN
Efficiency (%)
VIN
3V To 5V
L
22uH
SW
90k
5k
AP1521
SHDN
FB
R1
4Ω
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603ZD105
D: CENTRAL CMDSH2-3
L: MURATA LQH3C220
85
83
81
79
77
75
73
71
69
67
AP1521 Efficiency(%) v.s. LED
Current (mA)
Vin=4.2V
Vin=3.6V
Vin=5V
0
10
20
30
LED Current (mA)
40
50
Li-lon to Three White LEDs
D
CIN
1uF
COUT
0.22uF
VDC
Dimming
VIN
Efficiency (%)
VIN
3V To 5V
L
22uH
SW
90k
5k
AP1521
SHDN
FB
R1
4Ω
GND
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
85
83
81
79
77
75
73
71
69
67
AP1521 Efficiency(%) v.s. LED
Current (mA)
Vin=4.2V
Vin=5V
Vin=3.6V
0
10
20
30
40
LED Current (mA)
50
60
Li-lon to Four White LEDs
D
CIN
1uF
COUT
0.22uF
VDC
Dimming
VIN
SW
AP1521
SHDN
FB
GND
AP1521 Efficiency(%) v.s. LED
Current (mA)
Efficiency (%)
VIN
3V To 5V
L
22uH
90k
5k
R1
4Ω
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
85
83
81
79
77
75
73
71
69
67
Vin=5V
Vin=4.2V
Vin=3.6V
0
10
20
30
40
50
LED Current (mA)
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Rev. 0.1
6/8
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Typical Performance Characteristics (Continued)
Li-lon to Five White LEDs
D
CIN
1uF
COUT
0.22uF
VDC
Dimming
VIN
SW
90k
5k
AP1521
SHDN
FB
R1
6.8Ω
GND
AP1521 Efficiency(%) v.s. LED
Current (mA)
Efficiency (%)
VIN
3.3V To 5V
L
22uH
84
81
78
75
72
69
66
63
60
57
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
Vin=5V
Vin=3.6V
0
10
20
Vin=4.2V
30
LED Current (mA)
40
50
Li-lon to Six White LEDs
D
CIN
1uF
COUT
0.22uF
VDC
Dimming
VIN
SW
90k
5k
AP1521
SHDN
FB
R1
6.8Ω
GND
AP1521 Efficiency(%) v.s. LED
Current (mA)
Efficiency (%)
VIN
3.6V To 5V
L
22uH
84
81
78
75
72
69
66
63
60
57
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
Vin=5V
Vin=4.2V
Vin=3.6V
0
10
20
30
LED Current (mA)
40
50
Step up DC-DC Regulator
VOUT
4.8V
D
CIN
1uF
COUT
0.22uF
15K
VIN
SW
AP1521
FB
SHDN
GND
1K
90
Efficiency (%)
VIN
2.5V~3.3V
L
22uH
AP1521 Efficiency(%) v.s. Load
Current (mA)@Vout=4.8V
85
Vin=3.3V
Vin=2.5V
80
75
70
65
60
0
CIN: TAIYO YUDEN JMK107BJ105
COUT: AVX 0603YD224
D: CENTRAL CMDSH-3
L: MURATA LQH3C220
Anachip Corp.
www.anachip.com.tw
10
20
30
Load Current (mA)
Rev. 0.1
7/8
40
50
Apr. 27, 2004
AP1521
White LED Step-Up Converter
„ Marking Information
4
7
5
XX Y M
Identification code
(See Appendix)
1
2
Appendix
Part
Number
AP1521
Month: A~L
Package
SOT23-5
Identification
Code
FZ
Year: 0-9
3
„ Package Information
Package Type: SOT23-5L
D
e1
θ 1(4x)
5
4
E1
E
A
0.10 C
5x
A2
Seating Plane
A1
1
2
θ 2(4x)
3
b
e
With
Plating
b1
C
C1
Gauge Plane
0.25 mm
θ
Base
Metal
L
b
Symbol
A
A1
A2
b
b1
c
c1
D
E
E1
L
L1
e
e1
θ
θ1
θ2
L1
Dimensions In Millimeters
Min.
Nom.
Max.
1.05
1.20
1.35
0.05
0.10
0.15
1.00
1.10
1.20
0.25
0.55
0.25
0.40
0.45
0.08
0.20
0.08
0.11
0.15
2.70
2.85
3.00
2.60
2.80
3.00
1.50
1.60
1.70
0.35
0.45
0.55
0.60 Ref.
0.95 Bsc.
1.90 Bsc.
o
o
o
5
10
0
o
o
o
3
5
7
8o
10o
6o
Anachip Corp.
www.anachip.com.tw
Dimensions In Inches
Min.
Nom.
Max.
0.041
0.047
0.053
0.002
0.004
0.006
0.039
0.043
0.047
0.010
0.022
0.010
0.016
0.018
0.003
0.008
0.003
0.004
0.006
0.106
0.112
0.118
0.102
0.110
0.118
0.059
0.063
0.067
0.014
0.018
0.022
0.024 Ref.
0.037 Bsc.
0.075 Bsc.
o
o
o
0
5
10
o
o
o
3
5
7
6o
8o
10o
Rev. 0.1
8/8
Apr. 27, 2004
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