DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
General Description
Features
The AAT1402 is a step-up single channel LED driver with
an input voltage range of 2.7V to 5.5V. The wide input
voltage, small solution size, advanced dimming features
and high efficiency are suitable for LED backlight solutions
for single cell Li-ion based equipment. A precision high
voltage current sink maintains the maximum LED current
set by an external resistor from 10 to 31mA to drive 8
series connected LEDs. The high switching frequency supports ultra-small, low-cost filtering components.
• Input Voltage Range: 2.7 to 5.5V
• Drives up to 37V with 8 Series LEDs at 31mA
• 1MHz Switching Frequency Allows Small External
Components
• Up to 83% Efficiency with 10µH Inductor
• Dimming Control Options:
▪ 32 Steps - S2Cwire Single Wire Interface
▪ Filtered PWM
• Low Operating Current at 2.3mA
• Shutdown Current < 1µA
• Over-Voltage Protection for Open-LED Faults
• Over-Temperature Protection
• Ultra Small, Low Profile, 10-pin 1.55 x 1.15mm WLCSP
Package
Two dimming controls are available: 32 dimming steps
using S2Cwire and filtered PWM control. The frequency
range of the PWM dimming extends up to 100kHz, eliminating audible noise and making the AAT1402 suitable
for CABC (Content Adaptive Brightness Control) applications.
The AAT1402 includes over-temperature protection and
programmable over-voltage protection. The device is
available in a 10-pin wafer-level chip scale package
(WLCSP) and is rated over the -40°C to +85°C temperature range.
Applications
•
•
•
•
•
Digital Still Cameras (DSCs)
Mobile Handsets
Netbooks and Notebooks
Portable Media Players
White LED Drivers
Typical Application Circuit
Up to 8
WLEDs
D1
VIN
2.7V–5.5V
L1 10μH
R1
LX
IN
CIN
4.7µF
OVP
AAT1402
SC
PWM
2
COUT
0.1µF
R2
EN/SET
PWM
COMP
RSET
CCOMP
56nF
VOUT
Up to 37V
at 31mA
RSET
10k
CS
GND PGND
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1
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Pin Descriptions
Pin #
Symbol
A1
LX
A2
A3
B1
B3
C1
IN
EN/SET
PGND
PWM
GND
C3
COMP
D1
CS
D2
RSET
D3
OVP
Function
Switching node of boost converter. Connect an inductor between LX and input supply (VIN); Schottky rectifier anode is connected between LX pin while cathode is connected to output capacitor.
Supply input for the IC. Connect a 4.7µF, 6.3V/10V ceramic capacitor from this pin to GND.
Enable on/off control and S2Cwire interface input.
Power ground pin.
Input PWM pin. Pull high to disable the PWM dimming feature.
Ground pin.
Compensation pin. Connect a capacitor from this pin to GND. Compensation components vary with L and C
values used. See table in applications section.
Connect to the cathode of the last diode of the LEDs string.
Connect a resistor to GND to set maximum LED current. Drive this input with a resistor connected to an
analog voltage to dim the LED.
Feedback pin for over-voltage protection.
Pin Configuration
WLCSP-10
(1.1 x 1.5mm)
(Top View)
A1
A3
B1
B3
C1
C3
D1
2
A2
D2
D3
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Absolute Maximum Ratings1
Symbol
Description
VIN
VLX
VCS
VEN/SET,VPWM, VRSET,
VCOMP, VOVP
IN to GND, PGND
LX to GND, PGND
SINK to GND, PGND
EN/SET, PWM, RSET, COMP, OVP to GND/PGND
Value
Units
-0.3 to 6.0
-0.3 to 44
-0.3 to 35
V
V
V
-0.3 to IN +0.3
V
Value
Units
Thermal Information2
Symbol
ΘJA
PD
TJ
TLEAD
Description
Thermal Resistance
Maximum Power Dissipation
Maximum Junction Operating Temperature
Maximum Soldering Temperature (at leads, 10 sec)
122
820
-40 to +155
300
C/W
mW
O
O
C
Recommended Operating Conditions
Symbol
VIN
VOUT
L1
FPWM-F
TAMB
Description
Input Supply Voltage
Boosted Output Voltage
Inductor Value
Input Filtered PWM Frequency
Ambient Temperature Range
Min
2.7
VIN + 3V
4.7
100
- 40
Typ
Max
Units
10
5.5
VOUT3
22
100,000
85
V
V
μH
Hz
˚C
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. Check Electrical Characteristics.
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3
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Electrical Characteristics1
VIN = 3.6V, CIN = 4.7µF, COUT = 0.1µF, L = 10µH, RSET = 10KΩ, TA = -40°C to 85°C unless otherwise noted. Typical values
are at TA = 25°C.
Symbol
VIN
VOUT
IQ
ISHDN
IQSW
RDS(ON)N
η
Fosc
TSS
DMAX
VOVP-T
VOVPH
TSD
THYS
VCS
ICS(ACC)
VRSET
EN/SET
VEN/SET (L)
VEN/SET (H)
tEN/SET(LOW)
tEN/SET(HI_MIN)
tEN/SET(HIMAX)
tEN/SET(OFF)
tEN/SET(LAT)
IEN/SET (LK)
PWM
VPWM(L)
VPWM(H)
IPWM(LK)
4
Description
Input Voltage Range
Maximum Output Voltage
Quiescent Supply Current
Input Shutdown Current
Input Switching Current
NMOS On-Resistance
Maximum Efficiency
Switching Frequency
Soft-Start Time
Maximum Duty Cycle
OUT Over-Voltage Protection Threshold
Over-Voltage Protection Hysteresis
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Current Sink Voltage
Current Sink Accuracy
RSET Voltage
EN/SET
EN/SET
EN/SET Input Low Time
EN/SET Minimum High Time
EN/SET Maximum High Time
EN/SET Input Off Timeout
EN/SET Latch Timeout
EN Input Leakage
Logic Threshold Low
Logic Threshold High
PWM Input Leakage
Conditions
Min
Typ
Max
Units
5.5
37
700
1
2.3
650
83
1
V
V
µA
µA
mA
mΩ
%
MHz
5
ms
2.7
VENSET = VIN
VENSET = 0V
VENSET = VIN
TA = 25°C
IOUT = 31mA
TA = 25°C
VENSET = VIN to 95% of output regulation,
CCOMP = 56nF
VOVP rising
IOUT = 31mA
RSET = 10KΩ
RSET = 10KΩ
VIN = 2.7V to 5.5V
VIN = 2.7V to 5.5V
430
94.0
1.1
27.9
1.2
75
155
15
500
31.0
1.206
1.3
34.1
0.4
1.4
0.3
100
VENSET = 5V, VIN = 5V
-1
VPWM = 5V, VIN = 5V
1.4
-1
75
75
500
500
1
0.4
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1
%
V
mV
°C
°C
mV
mA
V
V
V
µs
ns
µs
µs
µs
µA
V
V
µA
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
Quiescent Current vs. Input Voltage
Shutdown Current vs. Input Voltage
0.10
Shutdown Current (µA)
Quiescent Current (µA)
500
480
460
440
420
85°C
25°C
-40°C
400
380
2.7
3.1
3.5
3.9
4.3
4.7
5.1
85°C
25°C
-40°C
0.08
0.06
0.04
0.02
0.00
5.5
2.7
3.1
3.5
Input Voltage (V)
VIN = 2.7V
VIN = 3.0V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
4
8
12
16
20
24
28
24
20
16
12
8
4
0
32
1
5
9
13
Output Current (mA)
17
21
25
29
33
S2C Data
Startup Time vs. CCOMP
LED Current Accuracy vs. Input Voltage
(VIN = 3.6V; ILED = 31mA; 8 LEDs)
(VIN = 3.6V, RSET = 15KΩ)
12
20.8
10
20.4
8
tSS (ms)
21.2
20.0
19.6
6
4
2
19.2
18.8
2.7
5.5
RSET = 10KΩ
RSET = 15KΩ
RSET = 20KΩ
RSET = 25KΩ
RSET = 30KΩ
28
0
5.1
(VIN = 3.6V, L = 10µH)
32
Current (mA)
Efficiency (%)
4.7
LED Current Accuracy vs. S2C
(RSET = 10KΩ, L = 10µH, 8 LEDs)
Current (mA)
4.3
Input Voltage (V)
Efficiency vs. Output Current
90
85
80
75
70
65
60
55
50
45
40
35
30
3.9
0
3.0
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
10
20
30
40
50
60
70
80
90
100
CCOMP (nF)
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
LED Current Accuracy vs. Temperature
LED Current Accuracy vs. Temperature
(VIN = 3.6V, RSET = 15kΩ)
31.8
20.8
31.4
20.4
Current (mA)
Current (mA)
(VIN = 3.6V, RSET = 10kΩ)
31.0
30.6
19.6
19.2
30.2
29.8
-40
-15
10
35
60
18.8
-40
85
Temperature (°C)
-40°C
25°C
85°C
0.9
0.9
0.8
VEN(L) (V)
1.0
0.8
0.7
85°C
25°C
-40°C
0.6
0.5
3.5
3.9
4.3
4.7
5.1
85
-40°C
25°C
85°C
0.7
0.6
85°C
25°C
-40°C
0.4
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
PWM Input High Threshold Voltage
vs. Input Voltage
PWM Input Low Threshold Voltage
vs. Input Voltage
1.1
1.0
85°C
25°C
-40°C
1.0
0.9
0.9
VPWM(L) (V)
VPWM(H) (V)
60
0.5
Input Voltage (V)
0.8
0.7
0.6
0.8
0.7
0.6
85°C
25°C
-40°C
0.5
0.5
0.4
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
6
35
EN Input Low Threshold Voltage
vs. Input Voltage
1.0
3.1
10
Temperature (°C)
1.1
2.7
-15
EN Input High Threshold Voltage
vs. Input Voltage
VEN(H) (V)
20.0
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
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5.1
5.5
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
OVP Low Threshold Voltage vs. Input Voltage
1.22
1.13
1.20
1.11
VOVP(L) (V)
VOVP(H) (V)
OVP High Threshold Voltage vs. Input Voltage
1.18
1.16
85°C
25°C
-40°C
1.14
1.12
2.7
3.1
1.09
1.07
1.05
1.03
3.5
3.9
4.3
4.7
5.1
5.5
2.7
85°C
25°C
-40°C
3.0
Input Voltage (V)
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
NMOS RDS(ON)N vs. Input Voltage
1000
Startup Waveform
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 10KΩ, 8 WLEDs)
85°C
25°C
-40°C
900
RDS(ON) (mΩ)
3.5
EN
(5V/div)
800
0
VOUT
(20V/div) 0
IIN
0
(200mA/div)
700
600
ILED
(20mA/div)
500
400
2.7
3.1
3.5
3.9
4.3
4.7
5.1
Input Voltage (V)
0
5.5
Time (2ms/div)
Turn Off
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 10KΩ, 8 WLEDs)
EN
(5V/div)
0
VOUT
(20V/div)
IIN
(200mA/div)
0
ILED
(20mA/div)
0
0
Time (100µs/div)
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7
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
Operation Waveform
Operation Waveform with 50kHz PWM Control
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 15KΩ, 8 WLEDs)
VLX
(20V/div)
IINDUCTOR
(500mA/div)
VOUT (AC)
(500mV/div)
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,CCOMP = 56nF,
RSET = 10KΩ, PWM = 50kHz, 50% Duty Cycle, 8 WLEDs)
VLX
(20V/div)
0
IINDUCTOR
(500mA/div) 0
VOUT (AC)
0
(500mV/div)
0
0
ILED
(20mA/div)
ILED
(20mA/div)
0
Time (1µs/div)
LED Current Transition by PWM
0
ILED
(20mA/div)
0
0
ILED
(20mA/div)
Time (400µs/div)
0
Time (400µs/div)
LED Current Transient by S2Cwire
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10KΩ, S2Cwire Data 1 to 16, 8 LEDs)
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10KΩ, S2Cwire Data 16 to 1, 8 LEDs)
EN/SET
(5V/div) 0
VOUT
(20V/div)
0
0
0
IIN
(200mA/div)
ILED 0
(20mA/div)
ILED
(20mA/div)
0
Time (400µs/div)
8
0
LED Current Transient by S2Cwire
IIN
(200mA/div)
LED Current Transition by PWM
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10kΩ, PWM = 10KHz, 15mA to 31mA, 8 LEDs)
IIN
(200mA/div)
0
EN/SET
(5V/div)
VOUT
(20V/div)
Time (1µs/div)
PWM
(5V/div) 0
VOUT
(20V/div)
0
IIN
(200mA/div)
0
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10KΩ, PWM = 10KHz, 31mA to 15mA, 8 LEDs)
PWM
(5V/div)
VOUT
(20V/div)
0
0
0
Time (400µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Functional Block Diagram
LX
PGND
IN
Control
OVP
OVP
OSC
REF
COMP
RSET
CS
EN/SET
Interface
PWM
GND
Functional Description
Soft Start / Enable
The AAT1402 is a high frequency current mode controlled
step-up (boost) converter LED driver. The device utilizes
a single current sink to regulate the LED current by controlling the output voltage. The wide voltage range is
suitable for single cell Li-ion / Li-polymer battery applications. The internal current sink is programmed by an
external resistor to a current from 10mA to 31mA. The
minimum output voltage must be greater than the input
voltage. The AAT1402 is capable of driving up to 8 series
connected LEDs with currents up to 31mA.
The AAT1402 is enabled by EN/SET pulled to high after
power on with a certain delay time. Soft start limits the
current surge seen at the input and eliminates output
voltage overshoot. When ENSET is pulled low the
AAT1402 enters a low-power, non-switching state. The
total input current during shutdown is less than 1μA. The
external Schottky diode makes VOUT equal to the level of
VIN during shutdown. The diode consumes a small
amount of additional input current depending on the OVP
resistor divider value.
The over-voltage protection function protects the boost
converter from open circuit LED string faults. The overtemperature function protects the converter if an overtemperature fault occurs. The AAT1402 will recover to
normal operation automatically when the OVP or OTP
fault is removed.
Over-Temperature Protection
Thermal protection disables the AAT1402 when internal
dissipation becomes excessive. Thermal protection disables the power MOSFET. The junction over-temperature
threshold is 155°C with 15°C of temperature hysteresis.
The output voltage automatically recovers when the
over-temperature fault condition is removed.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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9
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Over-Voltage Protection
S2Cwire™ Serial Interface
Over-voltage protection prevents damage to the AAT1402
LX pin during open-circuit or high output voltage conditions. An over-voltage event is defined as a condition
where the voltage on the OVP pin exceeds the over-voltage protection threshold (VOVP-T). When VOVP has reached
the threshold limit, the converter stop switching and the
output voltage decays. Switching resumes when the lower
hysteresis limit of VOVP is reached, thereby maintaining an
average output voltage between the upper and lower OVP
thresholds.
The LED current magnitude can be controlled by the EN/
SET pin using the S2Cwire interface. The interface records
rising edges of the EN/SET pin and decodes them into 32
individual current level settings. Code 1 is full scale
(maximum LED current), and Code 32 is 2% of the full
scale. The modulo 32 interface wraps states back to state
1 after the 32nd clock. The counter can be clocked at
speeds up to 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the IC and
initially sets the output LED current to full scale after
500µs tLAT. Once the final clock cycle is input for the
desired brightness level, the EN/SET pin should be held
high to maintain the device output current at the programmed level. The device is disabled 500μs after the
EN/SET pin enters a logic low state. The EN/SET timing
is designed to accommodate a wide range of data rates
from 20kHz to 1MHz.
LED Current Setting
The maximum LED current is determined by the RSET
resistor value. With a fixed 1.2V voltage on RSET, the LED
maximum current is a linear ratio to the current flowing
through RSET.
ILED =
VSET
· 258
RSET
After the first rising edge of EN/SET, the boost converter
is enabled and reaches full capacity after the soft-start
time. Exact counts of clock pulses for the desired current
level should be entered on the EN/SET pin with a single
burst of clocks. The counter refreshes each time a new
clock input to the EN/SET pin is detected. A constant current is maintained as long as EN/SET remains in a logic
high state. To save power, the boost converter is switched
off after EN/SET has remained in the low state for at least
the tOFF timeout period as shown in Figure 1.
The LED dimming is controlled via one of two options,
either using the 32-step S2Cwire single-wire interface via
the EN/SET pin or PWM control with varied duty cycle up
to 100kHz frequency. 32 S2Cwire rising-edge steps set the
LED current from 100% to 2% percentage of the maximum LED current value when PWM control is disabled by
pulling the PWM pin high. S2Cwire can also be used to set
maximum LED current along with a PWM signal to dim the
LED lighting from 100% to 1% of duty cycle.
S2Cwire Serial Interface Timing
THI
TLO
TOFF
T LAT
EN/SET
1
Data Reg
2
n-1
n ≤ 32
0
n
0
Figure 1: S2Cwire Timing Diagram.
10
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Application Information
Figure 2 illustrates the LED current value at different
S2Cwire code settings when RSET is 15kΩ with a maximum LED current of 20mA.
The maximum LED current is determined by value of the
external resistor RSET from 10mA to 31mA. The value of
RSET is determined by the voltage of RSET and the LED
current, and can be calculated by:
V · 258
RSET = SET
ILED
22
20
18
16
ILED (mA)
LED Current Setting
14
12
10
8
6
4
Maximum LED Current (mA)
RSET (kΩ)
31
20
15
12
10
10
15
20
25
30
Table 1: Examples of Standard 1% RSET Values for
Setting Maximum LED Current Levels.
LED current dimming is controlled either via the S2Cwire
single-wire interface through the EN/SET pin in 32 steps
or via PWM control with varied duty cycle up to 100kHz
frequency. The S2Cwire interface programs the LED current from the maximum LED current set by RSET to 2%
of the maximum LED current as shown in Table 2.
S2Cwire
Data
LED Current
(% IMAX)
S2Cwire
Data
LED Current
(% IMAX)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
100
97
94
90
87
84
81
77
74
71
68
65
61
58
55
52
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
48
45
42
39
35
32
29
26
23
19
16
13
10
6
3
2
2
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
ILED (mA)
Figure 2: S2Cwire Dimming Control
at Maximum LED Current (20mA max).
Filtered PWM Dimming
The AAT1402 provides a PWM input as an additional
means of providing dimming control for CABC applications. The LED current reduces percentage linearly as
the duty cycle decreasing. Frequencies of up to 100kHz
can be applied. To avoid output flicker and noise, the
input control PWM frequency is filtered by the low pass
filter composed of the error amplifier and the external
compensation capacitor.
Figure 3 shows the LED current dimming controlled by
yarying the PWM duty cycle at RSET = 15kΩ.
20
18
16
14
ILED (mA)
Where VSET = 1.2V. Table 1 lists examples of standard 1%
metal film RSET values for different maximum LED current
requirements.
12
10
8
6
4
2
0
100
90
80
70
60
50
40
30
20
10
0
PWM Duty Cycle (%)
Figure 3: Filtered PWM Dimming Duty Cycle vs.
Maximum LED Current (20mA max).
Table 2: S2Cwire Dimming Control
Current Settings.
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11
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Capacitor Selection
A compensation capacitor CCOM is used for step-up converter loop compensation, soft startup time control, and
PWM digital signal filtering. Loop compensation requires
matching values for CCOM, COUT, ILED, and VOUT:
COUT
ILED
<
CCOM 30 · 10-6 · VOUT
The AAT1402 can drive up to 8 white LEDs with forward
voltages up to 4V each. In a worst case with VF of 4V, a
COUT value of 0.1µF, and LED maximum current of 20mA,
the value of CCOM should be higher than 4.8nF.
CCOM >
COUT · 30 · VOUT
0.1 · 30 · 32
(nF) =
(nF) = 4.8nF
ILED
20
A higher value for CCOM lengthens the soft startup time.
The relationship between CCOM and startup time is almost
linear, with startup time x 105 magnification of CCOM; thus
56nF CCOM leads to a soft startup time of 5.6ms. Table 3
gives several examples of minimum CCOM values at different COUT and ILED and the step-up converter's operation
stable. Values of 56nF for CCOM and 0.1µF for COUT are
suitable in most cases.
COUT (µF)
VOUT (V)
CCOM_MIN (nF)
31
31
20
20
10
10
0.1
1
0.1
1
0.1
1
32
32
32
32
32
32
3.2
32
4.8
48
9.6
96
Inductor Selection
Inductor value, saturation current and DCR is most important parameter in selecting an inductor for AAT1402.
The suitable inductance range for the AAT1402 is 4.7µH
to 22µH. Higher inductance lowers the step-up converter's RMS current value. Together with lower DCR value
of the inductor, it makes the total inductor power loss
become much lower. Considering inductor size and cost,
10µH inductance is most suitable. Figure 4 illustrates
AAT1402 efficiency at different inductance with similar
DCR value.
Efficiency (%)
ILED (mA)
Multi-layer ceramic (MLC) capacitors provide small size
and adequate capacitance, low parasitic equivalent series
resistance (ESR) and equivalent series inductance (ESL),
and are well suited for use as input, output and compensation capacitors in the AAT1402 step-up converter LED
driver application. MLC capacitors of type X7R or X5R are
recommended to ensure good capacitance stability over
the full operating temperature range. A 4.7µF/6.3V input
capacitor is recommended and a 0.1µF/50V output capacitor is suitable as noted above. Table 4 lists some recommended capacitors for use with the AAT1402.
Table 3: Minimum CCOM Values vs. ILED and COUT
(Step-Up Converter Operation Stable).
90
85
80
75
70
65
60
55
50
45
40
35
30
4.7µH
10µH
22µH
0
4
8
12
16
20
24
28
32
Output Current (mA)
Figure 4: AAT1402 Efficiency at Different
Inductance with Similar DCR (VIN = 3.6V).
Manufacturer
Part Number
Value (µF)
Voltage (V)
Temperature Range
Case Size
Murata
GRM188R60J475K
GRM188R71H104KA93
4.7
0.1
6.3
50
X5R
X7R
0603
0603
Table 4: Examples of AAT1402 Input and Output Capacitor Selection.
12
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Considering the inductor copper loss, the inductor DCR
value together with the RMS current value flowing
through the inductor leads to inductor conduction loss
and also affects total efficiency. Larger DCR leads to
larger conduction loss and decreases total efficiency. The
inductor conduction loss can be estimated as shown in
the equation:
PL_LOSS = I2L_RMS · DCR
1
= · (I2L_MAX + I2L_MIN + IL_MAX · IL_MIN) · DCR
3
Efficiency (%)
IL_MAX and IL_MIN are the inductor peak current and minimum current. Figure 5 shows DCR effects on efficiency
with a 10µH inductor.
86
82
78
74
70
66
62
58
54
50
46
42
38
34
DC input current:
IIN =
VOUT · ILED
VIN · η
Inductor peak-to-peak current ripple:
IL_PP =
VIN · (VOUT - VIN)
VOUT · L · f
Inductor peak current:
IL_PEAK = IIN +
IL_PP VOUT · ILED VIN · (VOUT - VIN)
=
+
2
VIN · η
2 · VOUT · L · f
For example, for a white LED with 3.2V VF and 20mA
current at 81% efficiency with VIN less than 3.6V, the
inductor peak current is
IL_PEAK =
3.2 · 8 · 0.02
3.6 · (3.2 · 8 - 3.6)
+
= 330mA
3.6 · 0.81
2 · 3.2 · 8 · 10µ · 1M
Table 5 gives some examples of recommended inductors
for use with the AAT1402.
10µH DCR 235mΩ 3.2x3.2x1.55mm
10µH DCR164mΩ 4.0x4.0x2.0mm
10µH DCR 36mΩ 8.3x8.3x3.0mm
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32
ILED (mA)
Figure 5: Inductor DCR Effects on
Total Efficiency with 10µH at 3.6V VIN.
Inductor saturation current is also a key parameter in
selecting an inductor. For the step-up converter, the
peak inductor current is the DC input current plus half
the inductor peak-to-peak current ripple.
Manufacturer
Sumida
Murata
Coilcraft
Coiltronics
OVP Setting
Over-voltage protection is designed to protect the stepup converter from a LED string open fault. The OVP
threshold is 1.2V. For 8 white LEDs with VF up to 4V, the
resistor divider values for R1 and R2 can be calculated by:
R1 =
VOUT
- 1 · R2
VOVP_TH
Higher resistor divider values decrease the power loss
on the resistors. The total resistor value for 32V VOUT
should be less than 3.2MΩ for better noise immunity.
Values of 1.2MΩ for resistor R1 and 47kΩ for resistor R2
are recommended.
Part Number
Inductance
(µH)
Maximum DC ISAT
Current (mA)
DCR
(mΩ, typ)
Size (mm)
LxWxH
Type
CDRH3D18-100
CDRH3D23-220
LQH44PN100MP0L
LQH44PN220MP0L
EPL2014-103MLC
LPS4012-223MLC
SD18-100-R
10
22
10
22
10
22
10
900
550
1150
800
600
790
982
164
219
160
370
440
600
158
4.0x4.0x2.0
3.9x3.9x2.5
4.0x4.0x1.65
4.0x4.0x1.65
2.1x2.2x1.0
4.1x4.1x1.2
5.8x5.8x1.8
Shielded
Shielded
Non-shielded
Non-shielded
Shielded
Shielded
Shielded
Table 5: Example of AAT1402 Inductor Selection.
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13
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Rectifier Diode Selection
An external rectifier diode is required for the non-synchronous step-up converter. A low VF Schottky diode is
recommended. The diode voltage rating should be higher
than the OVP voltage. For an AAT1402 driving 8 white
LEDs with up to 4V forward voltage, the diode voltage
rating should be higher than 32V. Select a diode with DC
rated current equal to the input current to allow an adequate margin for safe use.
Manufacturer
Diodes
TSC
Printed Circuit Board
Layout Recommendations
For best performance of the AAT1402, the following
guidelines should be followed when designing the PCB
layout:
1. Make the power trace as short and wide as possible,
including the input/output power lines and switching
node, etc.
2. Make sure the ground bump connected to the printed circuit board with large copper area for better
thermal dissipation.
3. Put the input and output capacitor close to the IC as
close as possible to get the best filter result.
Part
Number
Maximum
DC Blocking
Voltage VR
(V)
Maximum
DC Forward
Current IF
(mA)
Non-repetitive
Peak Forward
Surge Current
IFSM (A)
Forward
Voltage
VF (V)
SDM20U40
40
250
1.0
0.37@20mA
DFLS160
60
1000
5.0
0.5@1A
SS15L
SS14L
50
40
1100
1100
30
30
0.51@0.5A
0.51@0.5A
Case
SOD523
PowerDI
123
Sub SMA
Sub SMA
Size WxLxH
(mm)
0.9x1.7x0.65
1.93x3.0x1.0
1.9x3.8x1.43
1.9x3.8x1.43
Table 5: Example of Typical Rectifier Diodes.
14
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
DS1
SDM20U40
L1
10μH
R1
1.2M
U1
AAT1402IUQ
J1
VIN
DC+
A2
CIN
4.7μF
DC -
LX
OVP
PWM
A1
D1
R2
47k
D3
D2
A3
EN/SET
B3
PWM
VIN
R3
51k
AAT1402
White LED
Driver
IN
J2
D3
D4
C3
COMP
D2
RSET
CCOM
D5
C1
GND
B1 PGND
56nF
RSET
15k
COUT
0.1μF /50V
CS
D1
D8
D7
D6
R4
51k
V_MCU
PWM
EN/SET
S2Cwire / PWM
Microcontroller
S2C
R7 R8 R9
1k 1k 1k
UP
U2
VDD
GP5
GP4
GP3
PIC12F675
VSS
GP0
GP1
GP2
C1
R5
0.1μF 1k
8
7
6
5
R6 51k
LED1
Red
VMCU
1
2
3
DOWN
1
2
3
4
J3
CYCLE
Figure 6: AAT1402 Evaluation Board Schematic.
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15
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Figure 7: AAT1402 Evaluation Board
Layout Top Layer.
Figure 8: AAT1402 Evaluation Board
Layout Top Layer (detail).
Figure 9: AAT1402 Evaluation Board Layout Bottom Layer.
16
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Component
Part Number
Description
Manufacturer
U1
U2
R1
R2
RSET
R3, R4, R6
R5, R7, R8, R9
CIN
COUT
C1
CCOM
D1, D2, D3, D4,
D5, D6, D7, D8
DS1
L1
LED1
CYCLE, UP, DOWN
AAT1402IUQ
PIC12F675
RC0603FR-071M2L
RC0603FR-0747KL
RC0603FR-0715KL
RC0603FR-0751KL
RC0603FR-071KL
GRM188R60J475K
GRM188R71H104K
GRM188R71C104K
GRM188R71C563K
High Efficiency Serial LED Driver for 8 White LEDs
8-Pin Flash-Based 8-Bit CMOS Microcontrollers
Res 1.2MΩ 1/10W 1% 0603 SMD
Res 47kΩ 1/10W 1% 0603 SMD
Res 15kΩ 1/10W 1% 0603 SMD
Res 51kΩ 1/10W 1% 0603 SMD
Res 1kΩ 1/10W 1% 0603 SMD
Cap Ceramic 4.7μF 0603 X5R 6.3V 10%
Cap Ceramic 0.1μF 0603 X7R 50V 10%
Cap Ceramic 0.1μF 0603 X7R 16V 10%
Cap Ceramic 0.05μF 0603 X7R 16V 10%
Skyworks
Microchip
RS-0805UW
20mA White LED 0805
Realstar
SDM20U40
CDRH3D18-100NC
0805KRCT
6*6*5
Surface Mount Schottky Barrier Diode
Power Inductor 10μH 0.9A SMD
Red LED 0805
12V 50mA Pushbutton
Diodes
Sumida
HB
E-LT
Yageo
Murata
Table 6: AAT1402 Evaluation Board Bill of Materials (BOM).
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17
DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Ordering Information
Package
Maximum # of LEDs
Interface
Marking
Part Number (Tape and Reel)
WLCSP-10
8
S2Cwire, Filtered PWM
H4YY
AAT1402IUQ-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
WLCSP-10
1.145 ± 0.035
ø 0.2 (Ref.)
Pin A1 indication
0.800 BSC
0.300
0.100
0.300
1.545 ± 0.035
Line_2
0.400 BSC
1.200 BSC
0.200 BSC
Line_1
0.100
Bottom View
Top View
0.380 ± 0.025
0.200 ± 0.025
0.070 ± 0.035
0.650 ± 0.085
0.265 ± 0.015
Side View
End View
All dimensions in millimeters.
1. YY = date code.
2. Sample stock is generally held on part numbers listed in BOLD.
18
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DATA SHEET
AAT1402
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
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Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.
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