202113A.pdf

DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
General Description
Features
The AAT1401 is a step-up single channel LED driver with
an input voltage range of 2.7V to 5.5V. The wide input
voltage range, small solution size, advanced dimming
features and high efficiency is 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.
The high switching frequency supports ultra small, low
cost filtering components.
• Input Voltage Range: 2.7 to 5.5V
• Drives up to 28V with 6 Series LEDs at 31mA
• 1MHz Switching Frequency Allows Small External
Components
• Up to 85% Efficiency
• 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 the S2Cwire™ interface, and filtered PWM control.
The frequency range of the PWM dimming extends up to
100 kHz eliminating audible noise and suitable for CABC
(Content Adaptive Brightness Control) applications.
The device includes over-temperature protection and
programmable over-voltage protection and recovers
automatically when the faults are removed. The AAT1401
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 (DSC)
Mobile Handsets
Netbooks and Notebooks
Portable Media Players
White LED Drivers
Typical Application
Up to 6
WLEDs
D1
VIN:
2.7V–5.5V
L1 10μH
R1
IN
CIN
4.7µF
OVP
AAT1401
SC
PWM
2
CCOMP
56nF
LX
RSET
10k
EN/SET
PWM
COMP
RSET
R2
VOUT:
Up to 28V
at 31mA
COUT
0.1µF
50V
CS
GND PGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
1
DATA SHEET
AAT1401
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
D2
D3
CS
RSET
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 are mainly
related to the output capacitor valued. See the Capacitor Selection section in the Application Information section of this datasheet.
Connect to the cathode of the last diode of the LED string.
Connect a resistor to GND to set maximum LED current up to 31mA.
Feedback pin for over-voltage protection.
Pin Configuration
WLCSP10 1.1 x1.5
(Top View)
A1
A3
B1
B3
C1
C3
D1
2
A2
D2
D3
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
DATA SHEET
AAT1401
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 34
-0.3 to 28
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
TA
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
3
DATA SHEET
AAT1401
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)
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
28
700
1
2.3
650
85
1.0
V
V
µA
µA
mA
mΩ
%
MHz
4
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
1
%
V
mV
°C
°C
mV
mA
V
V
V
µs
ns
µs
µs
µs
µA
V
V
µA
1. The AAT1401 is guaranteed to meet performance specification over the –40°C to +85°C operating temperature range, and is assured by design, characterization and correlation with statistical process controls.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
DATA SHEET
AAT1401
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
0.06
0.04
0.02
3.9
4.3
4.7
RSET = 10KΩ
RSET = 15KΩ
RSET = 20KΩ
RSET = 25KΩ
RSET = 30KΩ
28
VIN = 2.7V
VIN = 3.0V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
2
4
6
8
24
20
16
12
8
4
0
10 12 14 16 18 20 22 24 26 28 30 32
Output Current (mA)
1
5
9
13
17
21
25
29
33
S2C Data
Sink Current Accuracy vs. Temperature
Sink Current Accuracy vs. Temperature
(VIN = 3.6V, RSET = 15kΩ)
(VIN = 3.6V, RSET = 10kΩ)
32.0
21.2
31.6
Current (mA)
22.0
20.4
19.6
18.8
18.0
-40
5.5
(VIN = 3.6V, L = 10µH)
32
0
5.1
LED Current Accuracy vs. S2C
Current (mA)
Efficiency (%)
3.5
Input Voltage (V)
(RSET = 10KΩ, L = 10µH, 6 LEDs)
Current (mA)
3.1
Efficiency vs. Output Current
90
85
80
75
70
65
60
55
50
45
40
35
30
85°C
25°C
-40°C
0.00
2.7
5.5
Input Voltage (V)
0.08
31.2
30.8
30.4
-15
10
35
Temperature (°C)
60
30.0
-40
85
-15
10
35
60
85
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
5
DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
Startup Time vs. CCOMP
LED Current Accuracy vs. Input Voltage
(6 WLEDs)
(VIN = 3.6V, RSET = 15KΩ)
21.2
15
12
20.4
tSU (ms)
Current (mA)
20.8
20.0
19.6
6
3
19.2
18.8
2.7
9
0
3.1
3.5
3.9
4.3
4.7
5.1
10
5.5
Input Voltage (V)
0.9
0.9
0.8
VEN(L) (V)
VEN(H) (V)
1.0
0.8
0.7
85°C
25°C
-40°C
0.6
0.5
3.9
4.3
4.7
5.1
50
60
70
80
0.6
85°C
25°C
-40°C
0.4
5.5
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
NMOS RDS(ON)N vs. Input Voltage
85°C
25°C
-40°C
RDS(ON) (mΩ)
900
800
700
600
500
400
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
6
4.7
5.1
100
0.7
0.5
Input Voltage (V)
1000
90
EN Input Low Threshold Voltage
vs. Input Voltage
1.0
3.5
40
CCOMP (nF)
1.1
3.1
30
EN Input High Threshold Voltage
vs. Input Voltage
2.7
20
5.5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
5.1
5.5
DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
PWM Input Low Threshold Voltage
vs. Input Voltage
1.1
1.0
1.0
0.9
0.9
0.8
VPWM(L) (V)
VPWM(H) (V)
PWM Input High Threshold Voltage
vs. Input Voltage
0.8
0.7
85°C
25°C
-40°C
0.6
0.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
0.6
85°C
25°C
-40°C
0.5
0.4
5.5
Input Voltage (V)
2.7
3.1
1.25
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
OVP Low Threshold Voltage vs. Input Voltage
85°C
25°C
-40°C
1.23
1.20
85°C
25°C
-40°C
1.16
VOVP(L) (V)
1.21
1.19
1.17
1.12
1.08
1.04
1.15
1.00
2.7
3.1
3.5
3.9
4.3
4.7
5.1
Input Voltage (V)
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Startup Waveform
Turn Off
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 10KΩ, 6 LEDs)
EN
(5V/div)
3.5
OVP High Threshold Voltage vs. Input Voltage
VOVP(H) (V)
0.7
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 10KΩ, 6 LEDs)
EN 0
(5V/div)
0
VOUT
(10V/div) 0
IIN
0
(100mA/div)
VOUT 0
(20V/div)
IIN
0
(200mA/div)
ILED
(20mA/div) 0
ILED
(20mA/div)
Time (2ms/div)
0
Time (100µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
7
DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Typical Characteristics
Operation Waveform
Operation Waveform
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF,
CCOMP = 56nF, RSET = 10KΩ, 6 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, 6 WLEDs)
VLX
(20V/div)
0
IINDUCTOR
(500mA/div)
0
0
0
VOUT (AC)
(50mV/div) 0
0
ILED
(20mA/div) 0
ILED
(20mA/div)
0
Time (1µs/div)
LED Current Transient
LED Current Transition
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ,
PWM = 10KHz, Duty Cycle = 100% to 50%, 31mA to 15mA)
PWM
(5V/div)
VOUT
(20V/div)
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF, RSET = 10KΩ,
PWM = 10KHz, Duty Cycle = 50% to 100%, 31mA to 15mA)
PWM
(5V/div)
VOUT
(10V/div)
0
IIN
(200mA/div)
0
ILED
(20mA/div)
0
IIN
(100mA/div)
ILED
(20mA/div)
0
Time (1ms/div)
ILED
(20mA/div)
0
0
Time (1ms/div)
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10KΩ, S2Cwire Data 16 to 1)
EN/SET
(5V/div)
VOUT
(20V/div)
0
0
0
0
IIN
(200mA/div)
0
ILED
(20mA/div)
0
0
0
Time (1ms/div)
8
0
LED Current Transient by S2Cwire
(VIN = 3.6V; CIN = 4.7μF, COUT = 0.1μF, CCOMP = 56nF,
RSET = 10KΩ, S2Cwire Data 1 to 16)
IIN
(200mA/div)
0
LED Current Transient by S2Cwire
EN/SET
(5V/div)
VOUT
(20V/div)
Time (1µs/div)
Time (1ms/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
DATA SHEET
AAT1401
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 AAT1401 is a small size, high efficiency, current mode
controlled step-up converter LED driver for up to 6 white
LEDs. It is available with up to 28V output voltage to allow
up to 6 series connected LEDs to be driven with currents
up to 31mA. The device uses a single current sink to
regulate the LED current by controlling the output voltage. The maximum LED current is programmed by an
external resistor with range from 10mA to 31mA. The LED
current dimming is controlled via one of two options,
using either the S2Cwire 32-step single-wire interface or
PWM control.
The AAT1401 is enabled by EN/SET pulled to high after
power on with a certain delay time. Internal soft start
circuitry limits the input inrush current and eliminates
output voltage overshoot. When ENSET is pulled low the
AAT1401 enters a low-power, non-switching state. The
total input current during shutdown is less than 1μA. An
external diode limits VOUT 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 is designed to protect the boost converter during the fault of the open
circuit of the LED string. The over-temperature function
is targeted to protect the converter if an over-temperature fault occurs. The AAT1401 will recover to normal
operation automatically when the OVP or OTP fault is
removed.
Over-Temperature Protection
Thermal protection disables the AAT1401 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 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
9
DATA SHEET
AAT1401
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 AAT1401's
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 stops 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 • [email protected] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
DATA SHEET
AAT1401
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
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
4
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 AAT1401 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
varying 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
AAT1401
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 AAT1401 can drive up to 6 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 3.6nF.
CCOM >
COUT · 30 · VOUT
0.1 · 30 · 24
(nF) =
(nF) = 3.6nF
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
24
24
24
24
24
24
2.3
23
3.6
36
7.2
72
Inductor Selection
Inductor value, saturation current and DCR is most important parameter in selecting an inductor for AAT1401.
The suitable inductance range for the AAT1401 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
AAT1401 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 AAT1401 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 AAT1401.
Table 3: Minimum CCOM Values vs. ILED and COUT
(Step-Up Converter Operation Stable).
90
86
82
78
74
70
66
62
58
54
50
46
42
38
34
30
4.7µH
10µH
22µH
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32
ILED (mA)
Figure 4: AAT1401 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 AAT1401 Input and Output Capacitor Selection.
12
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DATA SHEET
AAT1401
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:
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.
90
86
82
78
74
70
66
62
58
54
50
46
42
38
34
30
VOUT · ILED
VIN · η
Inductor peak-to-peak current ripple:
IL_PP =
VIN · (VOUT - VIN)
VOUT · L · f
Inductor peak current:
PL_LOSS = I2L_RMS · DCR
=
DC input current: IIN =
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 82% efficiency, the inductor peak current is
IL_PEAK =
3.2 · 6 · 0.02
3.6 · (3.2 · 6 - 3.6)
+
= 276mA
3.6 · 0.82
2 · 3.2 · 6 · 10µ · 1M
Table 5 gives some examples of recommended inductors
for use with the AAT1401.
OVP Setting
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
Over-voltage protection is designed to protect the step-up
converter from a LED string open fault. The OVP threshold
is 1.2V. For 6 white LEDs with VF up to 4V, the resistor
divider values for R1 and R2 can be calculated by:
ILED (mA)
R1 =
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
VOUT
- 1 · R2
VOVP_TH
Higher resistor divider values decrease the power loss on
the resistors. The total resistor value for 24V VOUT should
be less than 2.4MΩ for better noise immunity. Values of
1MΩ for resistor R1 and 51kΩ 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 AAT1401 Inductor Selection.
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13
DATA SHEET
AAT1401
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 AAT1401 driving 6 white
LEDs with up to 4V forward voltage, the diode voltage
rating should be higher than 24V. Select a diode with DC
rated current equal to the input current to allow an adequate margin for safe use.
Manufacturer
Diodes
Central
TSC
Printed Circuit Board
Layout Recommendations
For best performance of the AAT1401, 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)
Case
Size WxLxH
(mm)
SDM20U40
SD103BW
CMDSH2-3
SS13L
SS14L
40
30
30
30
40
250
350
200
1100
1100
1.0
1.5
1.0
30
30
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
SOD523
SOD123
SDD323
Sub SMA
Sub SMA
0.9x1.7x0.65
1.7x3.85x1.35
1.35x2.6x1.0
1.9x3.8x1.43
1.9x3.8x1.43
Table 6: Example of Typical Rectifier Diode.
14
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Schematic and Layout
DS1
SDM20U40
L1 10µH
R1
1M
U1
AAT1401IUQ
J1
VIN
DC+
CIN
4.7µF
DC-
A2
A1
LX
D1
R2
51k
D3
OVP
PWM
D2
A3
EN/SET
B3 PWM
VIN
R3
51k
AAT1401
White LED
Driver
IN
J2
D3
C3
COMP
D2
RSET
CCOM
56nF
D4
C1
GND
B1 PGND
RSET
15k
COUT
0.1μF/50V
D1
CS
D6
D5
R4
51k
V_MCU
S2Cwire/PWM
Microcontroller
PWM
EN/SET
S2C
R7 R8 R9
1k 1k 1k
U2
1
2
3
4
UP
PIC12F675
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
C1
0.1µF
8
7
R6 51k
6
5
R5
1k
LED1
Red
VMCU
DOWN
3
2
1
J3
CYCLE
Figure 6: AAT1401 Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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15
DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Figure 7: AAT1401 Evaluation Board
Top Side Layout.
Figure 8: AAT1401 Evaluation Board
Top Side Layout (detail).
Figure 9: AAT1401 Evaluation Board Bottom Side Layout.
16
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Component
Part Number
Description
Manufacturer
U1
U2
R1
R2, R3, R4, R6
RSET
R5, R7, R8, R9
CIN
COUT
C1
CCOM
D1, D2, D3,
D4, D5, D6
DS1
L1
LED1
CYCLE, UP, DOWN
AAT1401
PIC12F675
RC0603FR-071ML
RC0603FR-0751KL
RC0603FR-0715KL
RC0603FR-071KL
GRM188R60J475K
GRM188R71H104K
GRM188R71C104K
GRM188R71C563K
High Efficiency Serial LED Driver for 6 White LEDs
8-Pin Flash-Based 8-Bit CMOS Microcontroller
Res 1MΩ 1/10W 1% 0603 SMD
Res 51KΩ 1/10W 1% 0603 SMD
Res 15KΩ 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 0.056μF 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 7: AAT1401 Evaluation Board Bill of Materials (BOM).
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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17
DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Ordering Information
Package
Maximum # of LEDs
Interface
Marking1
Part Number (Tape and Reel)2
WLCSP-10
6
S2C, Filtered PWM
F4YY
AAT1401IUQ-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
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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19