AAT2868 - Skyworks Solutions, Inc.

DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
General Description
Features
The AAT2868 is a low-noise, constant-frequency charge
pump DC/DC converter that uses a dual-mode load switch
(1x) and fractional (1.5x) conversion to maximize efficiency for white LED Content Adaptive Brightness Control
(CABC) applications. The AAT2868 is capable of driving 4
white LEDs at a total 124mA from a 2.7V to 5.5V input.
The current sinks may be operated individually or in parallel for driving higher-current LEDs. A low external parts
count (two 1µF flying capacitors and two small 1µF capacitors at IN and OUTCP) makes the AAT2868 ideally suited
for small battery-powered applications. The AAT2868 also
includes two 150mA low dropout (LDO) linear regulators
as additional power supplies for display and related camera power. The LDO voltage is also programmable.
• 2.7V to 5.5V Supply Voltage Range
• Charge Pump for LED Driver
▪ Dual Mode 1x/1.5x
▪ Drives Up to 4 LEDs with up to 31mA each
▪ Linear LED Output Control Options
•Maximum LED Current Set by AS2Cwire
Interface, 32 Steps
•PWM Interface Dimming from 100% to 1% Duty
Cycle with Frequency up to 100kHz
•0.9MHz Constant Frequency
•Automatic Soft-Start Limits Inrush Current
• Dual 150mA LDOs
▪ Enable and Output Voltage Set by AS2Cwire
Sixteen Combinations of 5 Output Voltages:
1.2V, 1.5V, 1.8V, 2.8V, and 3.0V
Integrated
Discharge Resistor when Disabled
▪
• < 1.0µA in Shutdown
• Short-Circuit Protection
• Small Application Circuit
• -40°C to 85°C Temperature Range
• RoHS Compliant, Halogen-Free TQFN3.0x2.2-18
Package
Skyworks’ Advanced Simple Serial Control™ (AS2Cwire™)
serial digital input is used to enable, disable and set the
maximum LED current to one of 32 levels for the LEDs.
The current ranges from 31mA to 0.4mA. An external
PWM input is adopted to dim the LED current from 100%
to 1% of the maximum LED current by varying the PWM
duty cycle with frequencies up to 100kHz. To eliminate
flicker or noise associated with PWM control, the input
PWM signal is filtered to provide a steady state output
current.
Applications
• Camera Phones
• Digital Still Cameras (DSC)
• LED Photo Flash/Torch
• MP3 Players
• PDAs and Notebook PCs
•Smartphones
Each output of the AAT2868 is equipped with built-in
protection for short-circuit and auto-disable for load
short-circuit conditions. The soft-start circuitry prevents
excessive inrush current at charge pump start-up and
mode transitions.
The AAT2868 is available in the Pb-free, space-saving
TQFN3.0x2.2-18L package, and operates over the -40°C
to 85°C ambient temperature range.
Typical Application
VIN
2.7~5.5V
C1
1µF
CIN
2.2µF
AS2Cwire
PWM
CF
56nF
C1+
C2+
C1C2IN
OUTCP
INLDO
AAT2868
EN/SET
PWM
FCAP
GND
D1
D2
D3
D4
LDOA
LDOB
AGND
C2
1µF
WLEDs
COUT
1µF
D1
D2
D3
D4
LDOA
LDOB
CLDOB
2.2µF
CLDOA
2.2µF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
1
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Pin Descriptions
Pin #
Symbol
Function
1
C1+
I
2
LDOB
O
3
LDOA
O
4
5
PWM
AGND
I
AG
6
INLDO
P
7
8
9
10
11
12
13
IN
GND
FCAP
D1
D2
D3
D4
P
PG
I
I
I
I
I
14
EN/SET
I
15
16
17
18
EP
C2C2+
OUTCP
C1-
I
I
O
I
Description
Flying capacitor C1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
LDOB output. Four output voltages can be programmed via the AS2Cwire interface: 1.2V, 1.5V,
1.8V and 2.5V. The default output voltage is 2.8V.
LDOA output. Four output voltages can be programmed via the AS2Cwire interface: 1.5V, 1.8V,
2.5V, and 3.0V. The default output voltage is 1.8V.
Connect a PWM signal up to 100kHz or tie to GND if PWM is not used.
Analog ground connection.
Input power supply pin to LDOs. Connect this pin to IN. A 1µF capacitor is recommended for
bypass use from this pin to ground.
Input power supply pin. Connect a 1µF bypass capacitor from this pin to ground.
Ground connection.
PWM filter capacitor. Connect a 56nF capacitor to ground. If PWM is not used, leave open.
LED driver current sink D1. Connect LED cathode to this pin. If not used, tie to OUTCP.
LED driver current sink D2. Connect LED cathode to this pin. If not used, tie to OUTCP.
LED driver current sink D3. Connect LED cathode to this pin. If not used, tie to OUTCP.
LED driver current sink D4. Connect LED cathode to this pin. If not used, tie to OUTCP.
Charge pump enable/set. When in the low state, AAT2868 is powered down, and consumes less
than 1µA. When EN/SET jumps from low to high, the charge pump is active and 20mA LED current each are set. The two LDOs remain inactive until data 3 is written to address 4 through the
AS2Cwire interface. This pin should not be left floating.
Flying capacitor C2 negative terminal. Connect a 1µF capacitor between C1+ and C1-.
Flying capacitor C2 positive terminal. Connect a 1µF capacitor between C2+ and C2-.
Charge pump output. Connect a 1µF bypass capacitor between this pin and ground.
Flying capacitor C1 negative terminal. Connect a 1µF capacitor between C2+ and C2-.
Exposed pad. Connect to ground directly beneath the package.
Pin Configurations
TQFN3.0 x 2.2-18
(Top View)
C1+
LDOB
LDOA
PWM
1
2
3
4
AGND
INLDO
IN
GND
FCAP
5
18
6
17
7
16
8
15
9
14
C1OUTCP
C2+
C2EN/SET
13
12
11
10
D4
D3
D2
D1
2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Absolute Maximum Ratings1
Symbol
VIN
VEN
VEN(MAX), VPWM (MAX)
IOUT
TJ
TLEAD
Description
Input Voltage
EN to GND Voltage
Maximum EN or PWM to Input Voltage or GND
Maximum DC Output Current (continuous)2
Maximum Junction Operating temperature
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to 6.0
VIN + 0.3
470
-40 to 150
300
V
V
V
mA
Value
Units
O
C
Thermal Information3
Symbol
θJA
θJC
PD
Description
Thermal Resistance from Junction to Ambient
Thermal Resistance from Junction to Case
Maximum Power Dissipation
66
39
1.5
O
O
C/W
C/W
W
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. Based on long-term current density limitation.
3. Mounted on an FR4 board.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
3
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Electrical Characteristics1
VIN = 3.6V; CIN = 1µF; COUT = 1µF; CFLY = 1µF; CFLT = 56nF; TA = -40°C to 85°C, unless otherwise noted. Typical values
are TA = 25°C.
Symbol
Description
Conditions
Input Power Supply
VIN
Input Voltage Range
VOUT(MAX)
Maximum Output Voltage
Icc
Operating Current
ISHDN(MAX)
Shutdown Current
Charge Pump Section
IOUT(MAX)
Maximum Output Current
fosc
Oscillator Frequency
tSS
Charge Pump Setup Time
VIN_(TH)
Charge Pump Mode Hysteresis
Min
Typ
Max
Units
5.5
V
V
2.7
1x Mode, No Load Current, CP enabled
1.5x Mode, ID1 = FS, excluding ID1, VD2 = VD3 =
VD4 = IN
EN = 0
5.5
0.5
1
2
4
1.0
VF = 3.6V
1.5x to 1x Transition, ID1 = ID2 = ID3 = ID4 =
31mA
mA
µA
124
0.9
100
mA
MHz
µs
300
mV
LED Current Sink Outputs
IDX
ISINK Current Accuracy2
Current Marching Between Any Two
Current Sinks3
VD_(TH)
Charge Pump Mode Transition
AS2Cwire Control and EN/SET Control
VEN/SET (L)
EN/SET
VEN/SET (H)
EN/SET
ILEAK
EN/SET Input Leakage
tEN/SET(LOW)
EN/SET Input Low Time
tEN/SET(HI_MIN) EN/SET Minimum High Time
tEN/SET(HI_MAX) EN/SET Maximum High Time
tEN/SET(OFF)
EN/SET Input Off Timeout4
tEN/SET(LAT)
EN/SET Latch Timeout5
PWM Control
VPWM(L)
PWM Input Low Threshold Voltage
VPWM(H)
PWM High Threshold Voltage
TPWM(ON)
PWM Turn On Delay
FPWM(MIN)
PWM Minimum Input Control Frequency
FPWM(MAX)
PWM Maximum Input Control Frequency
FPWM(MIN)
PWM Minimum Duty Cycle
IDX(MATCH)
Data 32 and PWM = 100%, TA = 25°C
Data 1-3, TA = 25°C
VF; D1:D4 = 3.6V
-10
+10
±15
-5
1x to 1.5x Mode, ID1 = ID2 = ID3 = ID4 = 31mA
%
+5
120
1.4
-1
0.3
250
mV
0.4
V
V
mA
µs
ns
µs
µs
µs
1
75
50
75
500
500
0.4
1.4
500
100
100
FPWM = 50kHz full scale
1
V
V
µs
Hz
kHz
%
1. The AAT2868 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
2. Determined by the average of all active channels.
3. Current matching is defined as the deviation of any sink current from the average of all active channels.
4. The EN/SET pin must remain logic low (less than VIL) for longer than 500μs to guarantee the off timeout.
5. The EN/SET pin must remain logic high (greater than VIH) for longer than 500μs to guarantee the latch timeout.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Electrical Characteristics (continued)1
VIN = 3.6V; CIN = 1µF; COUT = 1µF; CFLY = 1µF; CFLT = 56nF; TA = -40°C to 85°C, unless otherwise noted. Typical values
are TA = 25°C.
Symbol
Description
Linear Regulators
ΔVOUT[A/B]/
LDOA, LDOB Output Voltage Tolerance
VOUT[A/B]
IOUT[A/B](MAX) LDOA, LDOB Maximum Load Current
VOUT[A/B](DO) LDOA, LDOB2
∆VOUT/
Line Regulation
VOUT*∆VIN
PSRR[A/B]
LDOA, LDOB Power Supply Rejection Ratio
ROUT_(DCHG)
LDOA, LDOB Auto-Discharge Resistance
Thermal
TSD
TJ Thermal Shutdown Threshold
THYS
TJ Thermal Shutdown Hysteresis
Conditions
Min
IOUT = 1mA to 150mA; TA = 25°C
IOUT = 1mA to 150mA; TA = -40°C to +85°C
-2
-3.0
200
Typ
Max
Units
2
3.0
%
%
mA
mV
VOUT[A/B] ≥ 3.0V; IOUT = 150mA
100
150
VIN = (VOUT[A/B] + 1V) to 5V
0.09
%/V
IOUT[A/B] = 10mA, 1kHz
50
720
dB
Ω
140
20
°C
°C
1. The AAT2868 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
2.VDO[A/B] is defined as VIN – LDO[A/B] when LDO[A/B] is 98% of nominal.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
5
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
CP Operating Current vs. Input Voltage
CP Operating Current vs. Input Voltage
(1.5x Mode)
0.6
3.0
0.5
2.5
0.4
2.0
IQ (mA)
IQ (mA)
(1x Mode)
0.3
0.2
85°C
25°C
-40°C
0.1
0.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
1.5
1.0
0.0
2.7
5.5
Input Voltage (V)
ISD (µA)
Input Current (A)
4.7
5.1
5.5
VIN = 3.6V
VIN = 5.5V
0.08
0.06
0.04
0.02
40
3.1
3.5
3.9
4.3
4.7
5.1
0.00
-40
5.5
-15
10
35
60
85
Temperature (°C)
LDO Operating Current vs. Input Voltage
LDO Operating Current vs. Input Voltage
0.25
0.25
0.20
0.20
0.15
0.15
(LDOA Only)
IOP (mA)
(LDOA + LDOB)
IOP (mA)
4.3
0.10
80
Input Voltage (V)
0.10
85°C
25°C
-40°C
0.05
0.00
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
6
3.9
Shutdown Current vs. Temperature
120
0
2.7
3.5
VF = 3.3V, ILED = 31mA
VF = 3.2V, ILED = 20mA
VF = 3.1V, ILED = 10mA
VF = 2.9V, ILED = 5mA
160
3.1
Input Voltage (V)
CP Input Current vs. Input Voltage
200
85°C
25°C
-40°C
0.5
4.7
5.1
0.10
85°C
25°C
-40°C
0.05
0.00
2.7
5.5
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
5.1
5.5
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
Frequency vs. Temperature
CP Efficiency vs. Input Voltage
100
80
Frequency (KHz)
90
Efficiency (%)
950
VF = 3.3V, ILED = 31mA
VF = 3.2V, ILED = 20mA
VF = 3.1V, ILED = 10mA
VF = 2.9V, ILED = 5mA
70
60
50
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
910
890
870
850
-40
5.5
Input Voltage (V)
930
32.5
85
(VIN = 3.6V; VF = 3.3V; 0.5mA/ch)
0.50
D1
D2
D3
D4
0.46
Current (mA)
30.9
60
CP Current Matching vs. Temperature
D1
D2
D3
D4
31.7
35
Temperature (°C)
(VIN = 3.6V; VF = 3.3V; 31mA/ch)
Current (mA)
10
CP Current Matching vs. Temperature
30.1
29.3
0.42
0.38
0.34
28.5
-40
-15
10
35
60
0.30
-40
85
Temperature (°C)
1.0
1.8
0.2
-0.2
-0.6
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
60
85
(VOUT = 1.2V)
Output Error (%)
0.6
35
LDO Load Regulation vs. Output Current
85°C
25°C
-40°C
3.1
10
Temperature (°C)
(VOUT = 1.2V)
-1.0
2.7
-15
LDO Line Regulation vs. Input Voltage
Output Error (%)
-15
0.6
0.0
-0.6
-1.2
-1.8
0.1
5.5
85°C
25°C
-40°C
1.2
1
10
100
1000
Load Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
7
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
EN Input Low Threshold Voltage
vs. Input Voltage
1.2
1.2
1.0
1.0
VEN(L) (V)
VEN(H) (V)
EN Input High Threshold Voltage
vs. Input Voltage
0.8
0.6
-40°C
25°C
85°C
0.4
0.2
2.7
3.1
3.5
3.9
4.3
4.7
5.1
0.8
0.6
0.2
2.7
5.5
Input Voltage (V)
1.0
VPWM(L) (V)
VPWM(H) (V)
1.0
0.8
0.6
-40°C
25°C
85°C
0.4
3.9
4.3
4.7
5.1
5.1
5.5
0.6
-40°C
25°C
85°C
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
EN/SET Input Off Time vs. Input Voltage
320
360
tEN/SET(OFF) (µs)
280
tEN/SET(LAT) (µs)
4.7
0.8
0.2
2.7
5.5
EN/SET Input Latch Time vs. Input Voltage
240
200
85°C
25°C
-40°C
160
3.1
3.5
3.9
4.3
Input Voltage (V)
8
4.3
0.4
Input Voltage (V)
120
2.7
3.9
PWM Input Low Threshold Voltage
vs. Input Voltage
1.2
3.5
3.5
Input Voltage (V)
1.2
3.1
3.1
PWM Input High Threshold Voltage
vs. Input Voltage
0.2
2.7
-40°C
25°C
85°C
0.4
4.7
5.1
300
240
180
120
2.7
5.5
85°C
25°C
-40°C
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
5.1
5.5
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
CP Turn On
CP Turn Off
(VIN = 3.6V; CIN = COUT = 1µF; CF = 56nF; 20mA/ch)
(VIN = 3.6V; CIN = COUT = 1µF; CF = 56nF; 31mA/ch)
EN
(2V/div)
EN
(2V/div)
0
IIN
(100mA/div)
IIN
(200mA/div)
0
VOUT
(2V/div)
0
VOUT
(2V/div)
ILED
(20mA/div)
0
ILED
(20mA/div)
Time (100µs/div)
0
0
0
0
Time (100µs/div)
CP Current Transient
CP Current Transient
(VIN = 3.6V; 0.5mA to 31mA)
VEN
(2V/div)
VOUT
(5V/div)
IIN
(200mA/div)
ILED
(20mA/div)
(VIN = 3.6V; 31mA to 0.5mA)
0
VEN
(2V/div)
VOUT
(5V/div)
0
IIN
(200mA/div)
0
ILED
(20mA/div)
0
Time (100µs/div)
LDO Turn On
IIN
(1A/div)
VLDOA
(2V/div)
VLDOB
(2V/div)
0
0
LDO Turn On
(VIN = 3.6V; CIN = 2.2µF; CLDOA = CLDOB = 2.2µF;
VLDOA = 3.0V; VLDOB = 1.8V)
EN
(2V/div)
0
IIN
(1A/div)
VLDOA
(2V/div)
0
0
VLDOB
(2V/div)
0
Time (40µs/div)
0
Time (40µs/div)
(VIN = 3.6V; CIN = 2.2µF; CLDOA = CLDOB = 2.2µF;
VLDOA = 2.8V; VLDOB = 1.2V)
EN
(2V/div)
0
0
0
0
0
Time (40µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
9
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
LDO Turn Off
1.5x Mode Operating Characteristics
(VIN = 3.2V; CIN = COUT = 1µF; 31mA/ch)
(VIN = 3.6V; CIN = 2.2µF; CLDOA = CLDOB = 2.2µF;
VLDOA = 2.8V; VLDOB = 1.2V)
EN
(2V/div)
VLDOA
(2V/div)
VLDOB
(2V/div)
VIN
(AC coupled)
(50mV/div)
VOUT
(AC coupled)
(50mV/div)
IIN
(200mA/div)
ILED
(20mA/div)
0
0
0
0
0
0
0
Time (1ms/div)
Time (1µs/div)
1.5x Mode Operating Characteristics
VIN
(AC coupled)
(50mV/div)
VOUT
(AC coupled)
(50mV/div)
IIN
(100mA/div)
ILED
(20mA/div)
CP Mode Transient
(VIN = 3.2V; CIN = COUT = 1µF; PWM;
100kHz; Duty = 50%; 31mA/ch)
(VIN = 3.6V to 4.2V; CIN = COUT = 1µF; 31mA/ch)
VIN
(2V/div)
0
3.6V
0
VOUT
(2V/div)
0
0
ILED
(20mA/div)
0
4.2V
0
0
Time (1µs/div)
Time (100µs/div)
LDO Load Transient
(VIN = 3.6V; VOUTB = 1.2V; CIN = COUTB = 2.2µF;
10mA to 150mA)
IOUTB
(50mA/div)
0
VOUT
(2V/div)
0
Time (40µs/div)
10
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Typical Characteristics
Dropout Characteristics
Dropout Characteristics
(VOUTA = 2.8V)
(VOUTA = 3.0V)
3.6
IOUT = 0mA
IOUT = 10mA
IOUT = 50mA
IOUT = 100mA
IOUT = 150mA
IOUT = 200mA
3.2
3.0
Output Voltage (V)
Output Voltage (V)
3.4
2.8
2.6
2.4
2.7
2.8
2.9
3.0
3.1
3.2
3.0
IOUT = 0mA
IOUT = 10mA
IOUT = 50mA
IOUT = 100mA
IOUT = 150mA
IOUT = 200mA
2.8
2.6
2.4
2.7
3.2
Input Voltage (V)
3.4
2.8
2.9
3.0
3.1
3.2
Input Voltage (V)
PSRR vs. Frequency
(VIN = 3.6V, VRIPPLE = 500mVPP, CIN = COUT = 2.2μF, IL = 10mA)
100
PSRR (dB)
80
60
40
20
0
0.1
1
10
Frequency (KHz)
100
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Functional Block Diagram
IN
C1+
C1C2+
C2-
Dual-mode
Charge Pump
1X/1.5X
4
FCAP
PWM
EN/SET
OUTCP
PWM Filter
Control
Logic
32-step AS2Cwire
Backlight Control
and LDO Setting
INLDO
D1
D2
D3
D4
LDOA
LDOB
GND
Functional Description
The AAT2868 is a high efficiency charge pump white LED
driver for portable applications. It can drive up to 4 white
LEDs. And the integrated two LDOs can provide 1.2V,
1.5V, 1.8V, 2.8V and 3.0V output voltages with 16 combinations with up to 150mA load capability.
The charge pump of AAT2868 is a fractional charge pump
and can multiply the input voltage by 1 or 1.5 times. The
charge pump switches at a fixed frequency of 0.9MHz.
The internal mode-selection circuit automatically switches
the mode between 1x and 1.5x based on the input voltage, white LED forward voltage VF, and the programmed
LED current. This mode switching maximizes the efficiency throughout the entire LED load range. When the
input voltage is high enough, the charge pump operates
in 1x mode (no charge pump) to provide maximum efficiency. If the input voltage is too low to supply the programmed LED current, typically when the battery discharges and the voltage decays, the 1.5x charge pump
mode is automatically enabled. When the battery is connected to a charger and the input voltage become high
enough again, the device will switch back to 1x mode.
12
AGND
Five registers are designed for charge pump enable/disable control, LED current programming, LDO enable/
disable control of the two LDOs, and combined LDO output voltage settings via the AS2Cwire interface. The LED
current value is controlled by either the AS2Cwire interface, a PWM interface, or both. The AS2Cwire interface
records rising edges of the EN/SET pin and decodes
them into 32 individual current level settings from 0.4mA
to 31mA, while the PWM interface receives an input
switching frequency where the duty cycle is varied to
modulate the output current. To avoid switching noise
and flicker in the output LED, the input PWM frequency
is filtered via an internal resistor and small external
capacitor to provide a constant LED current. Once the
AAT2868 charge pump is enabled, the PWM input will
modulate the current up to the maximum current programmed by the AS2Cwire interface.
AS2C Registers
The AAT2628 has five registers with up to four bits each
to control the LED backlighting enable/disable, LED current and two LDOs enable/disable, output voltages, etc.
as shown in Table 1. Each register data can be written
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Address
Data
Number
EN/SET
Rising Edges
Function
D3
D2
D1
D0
EN/SET
Rising Edges
0 [Default]
1
2
3
4
5
17
19
20
21
22
Backlight Enable
Reserved
Backlight MSB
Backlight LSBs
LDO Enable Control
LDO Output Voltage
0
0
BL[3]
0
LDO[3]
BL_ENB
0
BL[2]
0
LDO[2]
0
0
BL[1]
LDOA_EN
LDO[1]
0
BL[4]
BL[0]
LDOB_EN
LDO[0]
1 or 5
1 or 2
1 ~ 16
1~4
1 ~ 16
Table 1: AAT2868 AS2C Registers.
with 1 to 16 EN/SET rising edges. Some bits are internally reserved and customer should only write it by bit
zero, such as Address 0, bit D0, D1 and D3, etc.
Otherwise it may lead to unexpected result. Address 0 is
the default address; if EN/SET is pulled high after a low
level of at least 500µs tOFF duration, address 0 is written
by 0 and LED backlighting is enabled with the default
20mA LED current each.
Address 0 – Backlight Enable
The BL_ENB bit of address register 0 is adopted to enable
or disable white LED backlighting. 0 enables backlighting;
1 disables backlighting. The other bits of the register
should be written by zero.
Description
BL_ENB
Backlight On [default]
0
Backlight Off
1
Table 2: AS2C Register Address 0 Settings.
Address 2 and 3 –
LED Current Level Settings
LED current level is set via the AS Cwire interface in a
linear scale by 32 codes where LED current of each
higher code is higher than the lower one, as shown in
Table 2. In this manner, the LED current decreases linearly with each decreasing code.
2
LED
Current
Codes
Addr2
Addr3
BL4
BL3
BL2
BL1
BL0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
21
1
0
1
0
0
22
23
24
25
26
27
28
29
30
31
32
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
0
1
LED
Current
(mA)
0.4
0.9
1.9
2.9
3.9
4.9
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
[Default]
21.0
22.0
23.0
24.0
25.0
26.0
27.0
28.0
29.0
30.0
31.0
Table 3: AS2C Register Address 2 and Address 3
LED Current Settings1.
1. The LED current accuracy is compromised at low code settings.
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Address 4 – LDO Enable Control
Address 5 - LDO Voltage Output Settings
The AAT2868 includes two low dropout (LDO) linear
regulators. These regulators are powered from the battery and produce a fixed output voltage set through the
AS2Cwire serial interface. AS2C address 4 register is
used to turn the two LDOs on/off via the AS2Cwire serial
interface. An internal resistor is used to discharge the
LDO output voltage when the LDO is disabled.
Register address 5 is used to set LDOA and LDOB output
voltage levels. Sixteen combinations of the two LDOs can
be programmed by the 4 bits of the register. LDOA can
be set to one of four levels: 1.5V, 1.8V, 2.8V or 3.0V.
LDOB can be set one of four levels: 1.2V, 1.5V, 1.8V or
2.8V. The LDO regulators require only a small 2.2μF
ceramic output capacitor for stable operation. If improved
load transient response is required, larger-valued capacitors can be used without stability degradation.
Data
Description
LDOA Off, LDOB
[Default]
LDOA Off, LDOB
LDOA On, LDOB
LDOA On, LDOB
Off
On
Off
On
LDOA_EN
LDOB_EN
EN/SET
Rising
Edges
0
0
1
0
1
1
1
0
1
2
3
4
AS2Cwire EN/SET Interface
The AAT2868 is dynamically programmable using the
AS2Cwire single-wire interface. AS2Cwire records rising
edges detected at the EN/SET pin to address and load
the data registers. The timing diagram in Figure 1 shows
the typical transmission protocol.
Table 4: AS2C Register Address 4 Settings.
Data
Description
LDO[3]
LDO[2]
LDO[1]
LDO[0]
EN/SET Rising Edges
LDOA = 3.0V, LDOB = 2.8V
LDOA = 3.0V, LDOB = 1.8V
LDOA = 3.0V, LDOB = 1.5V
LDOA = 3.0V, LDOB = 1.2V
LDOA = 2.8V, LDOB = 2.8V
LDOA = 2.8V, LDOB = 1.8V
LDOA = 2.8V, LDOB = 1.5V
LDOA = 2.8V, LDOB = 1.2V
LDOA = 1.8V, LDOB = 2.8V [default]
LDOA = 1.8V, LDOB = 1.8V
LDOA = 1.8V, LDOB = 1.5V
LDOA = 1.8V, LDOB = 1.2V
LDOA = 1.5V, LDOB = 2.8V
LDOA = 1.5V, LDOB = 1.8V
LDOA = 1.5V, LDOB = 1.5V
LDOA = 1.5V, LDOB = 1.2V
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Table 5: AS2Cwire Register Address 5 LDOA and LDOB Output Voltage Settings.
14
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Address
TLO
Data
TLAT
T LAT
THI
EN/SET
1
2
19
20
1
2
n ≤ 16
Address
0
Data Reg
3
0
n
Figure 1: AS2Cwire Timing Diagram.
The AAT2868 latches address or data after the EN/SET
input has been held high for time tLAT (500µs) through
AS2Cwire interface. Address or data is differentiated by
the number of EN/SET rising edges. Address has EN/SET
rising edges from 17 to 22 and data has EN/SET rising
edges from 1 to 16. A typical write protocol of the
AS2Cwire interface is a burst of EN/SET rising edges
identifying a particular address, followed by a pause with
EN/SET held high for the tLAT timeout period, then a burst
of rising edges signifying data, and another tLAT timeout
after the data has been sent. Once an address is set,
multiple writes to that address are allowed since the
address is not reset after each write. Address edges are
needed when changing the address, or writing to an
address other than the default after shutdown. Address
0 is the default address after shutdown. If the part is
enabled with only one rising edge after shutdown, then
Address 0 will be programmed and LED backlight channels BL1-BL4 will be enabled to the default 20mA each.
When EN/SET is held low for a time longer than tOFF
(500µs), the AAT2868 enters shutdown mode with
charge pump and two LDOs all turning off and draws less
than 1µA of current from IN. At shutdown, the data and
address registers are reset to 0.
PWM Control
The AAT2868 also includes an independent 20mA LED
current PWM dimming control with EN/SET low or an
additional means of providing dimming control after
maximum LED current set by EN/SET. When EN/SET is
low, up to 100kHz PWM signal with varied duty cycle
through PWM pin may change the LED current between
0mA and 20mA each.
When PWM is used as an additional dimming control,
before the PWM signal is activated, the EN/SET pin must
be held for the tLAT period after setting the maximum current available to the LEDs. For example, if the maximum
current of 20mA is required then a simple enable of the
EN/SET followed by tLAT will allow 20mA to flow through
each LED. By applying a variable duty cycle between 1%
and 100% on the PWM pin, this current can now be
adjusted. Frequencies of up to 100kHz can be applied. To
avoid output flicker and noise, the input control PWM
frequency is filtered by an internal resistor in conjunction
with an external filter capacitor. It is recommended that
a 56nF ceramic capacitor be used.
Short Circuit and
Over-Temperature Protection
The AAT2868 integrates short circuit protection to limit
the input current in the case of the charge pump output
or the two LDO outputs shorted to ground by fault. The
backlight and the two LDOs will recover to normal operating state once the fault is removed.
The AAT2868 also includes over-temperature protection
circuitry. When the junction temperature is too high, the
over-temperature protection circuitry is active and the IC
enters standby mode with no LED current or LDO output.
When the fault is removed, the LED backlighting and
LDO outputs all recover.
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15
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Address
TLO
Data
TLAT
TLAT
THI
EN/SET
1
2
19
1
20
2
n ≤ 16
PWM
(Up to 100kHz)
Figure 2: PWM Control Timing
Application Information
LED Selection
The AAT2868 is designed to drive high intensity white
flash LEDs with forward voltages up to 4.4V. Though
AAT2868 switches the charge pump mode 1x and 1.5x
mode automatically to maintain the continuous LED current accuracy, to obtain higher efficiency lower VF of the
white LEDs should be selected.
Maximum LED Current Setting
ILED (V)
32 maximum LED current codes from 0.4mA to 31mA can
be set by address registers 2 and 3 through the EN/SET
AS2Cwire interface as shown in Figure 3. To obtain linear
LED current change, the AAT2868 is designed not to
change the LED current when data is written only to
address 2. The control circuit writes data to both address
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6 7
8
9
2 and address 3 registers only after address 3 is written
to determine which LED current code is programmed.
Address 2 BL4's default value is 0 after one EN/SET rising
edge.
Code 1 to 16 with LED current from 0.4mA to 15mA can
be set after sending address 3 with 20 rising edges and
sending data with 1 to 16 rising edges after tLAT. Code 17
to 32 with LED current from 16mA to 31mA can be
obtained after writing both address 2 and address 3. The
operation is performed via the following steps:
1. Select address 2 by sending 19 rising edges on EN/
SET and holding high for tLAT;
2. Send data 1 to set DL4 by sending 2 rising edges
and holding high for tLAT;
3. Select address 3 by sending 20 rising edges on EN/
SET and holding high for tLAT;
4. Send data 15 to obtain LED current code 32 setting
by sending 16 rising edges on EN/SET and holding
high for tLAT.
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
LED Current Code
Figure 3: AAT2868 Total 32 LED Current Codes vs. LED Current.
16
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
LED Dimming by PWM
Charge Pump Efficiency
The external PWM input signal dims the LEDs linearly by
varying the duty cycle from 100% to 1%. Figure 4 shows
the varied PWM duty cycle vs. maximum 20mA LED current.
1x Mode Efficiency
CFLT is used as a RC filter capacitor to filter the PWM control signal to a constant voltage for internal LED current
control. With internal resistance of 200kΩ and the RC filter rejection frequency set to 1/20 of the PWM frequency,
the CFLT minimum value can be calculated by the following
formula:
20
CFLT = 2πR · f
The AAT2868's 1x mode is operational at all times and
functions alone to enhance device power conversion efficiency when VIN is higher than the voltage across the
load. When in 1x mode, voltage conversion efficiency is
defined as output power divided by input power.
η=
An expression for the ideal efficiency (η) in 1X charge
pump mode can be expressed as:
η=
PWM
Table 7 shows some minimum CFLT values for different
PWM frequencies. For most applications, 56nF is a suitable value except for 100Hz PWM frequency where a
value greater than 160nF should be used. If PWM control is not used, CFLT is unnecessary.
fPWM (kHz)
Minimum CFLT (nF)
0.1
1
10
30
50
80
100
159
15.9
1.6
0.5
0.3
0.2
0.2
POUT
PIN
POUT VF · IOUT
VF
=
≈
PIN
VIN · IIN
VIN
-or-
η(%) = 100
VOUT
VIN
1.5x Charge Pump Mode Efficiency
The AAT2868 contains a fractional charge pump which
will boost the input supply voltage in the event where VIN
is less than the voltage required to supply the output.
The efficiency (η) can be simply defined as a linear voltage regulator with an effective output voltage that is
equal to one and one half times the input voltage.
Efficiency (η) for an ideal 1.5x charge pump can be calculated by the following equation:
Table 7: Minimum CFLT Value Examples.
η=
-or-
VF · IOUT
VF
POUT VF · IOUT
=
=
≈
VIN · IIN
VIN · 1.5 · IOUT 1.5 · VIN
PIN
η(%) = 100
VOUT
1.5 · VIN
22
20
18
ILED (V)
16
14
12
10
8
6
4
2
0
100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
0
PWM Duty Cycle (%)
Figure 4: Linear Dimming by PWM Duty Cycle
(20mA Maximum LED Current).
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17
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Capacitor Selection
The AAT2868 needs seven capacitors for a typical application: CIN, COUT, C1, C2, CFLT and CLOA, CLOB. Among them,
CIN, C1, C2 and COUT are required for the 1.5x mode
charge pump. 1µF surface-mount multi-layer ceramic
capacitors with less than 100mΩ low equivalent series
resistance (ESR) are recommended. Though capacitor
ESR will not affect the ability of the capacitor to store
energy, it has a large effect on performance such as
equivalent output resistance, efficiency, and output voltage ripple of the charge pump. Tantalum and aluminum
electrolytic capacitors are not recommended for use with
the AAT2868 due to their high ESR. A output capacitance
value of 2.2µF or above is required for LDOA and LDOB
for proper load voltage regulation and stable operation.
Table 6 shows some recommended capacitors.
For most applications, ceramic capacitors with X5R temperature characteristics are preferred for AAT2868 application. These capacitors have good capacitance tolerance
over a wide temperature range (X5R: ±15% over -55°C
to +85°C). Capacitors with Y5V or Z5U temperature characteristics are generally not recommended for AAT2869.
They have wide capacitance tolerance over special temperature (Y5V: +22%, -82% over -30°C to +85°C, Z5U:
+22%, -56% over +10°C to +85°C).
Careful selection of the four external capacitors CIN, C1,
COUT is important because they will affect turn-on time,
output ripple and transient performance. Optimum per-
Manufacturer
Murata
TDK
formance will be obtained when low ESR (<100mΩ)
ceramic capacitors are used. In general, low ESR may be
defined as less than 100mΩ. A capacitor value of 1uF for
all four capacitors is a good starting point when choosing
capacitors. If the LED current sinks are only programmed
for light current levels, then the capacitor size may be
decreased.
Additional Applications
The current sinks of the AAT2868 can be combined to
drive higher current levels through a single LED. As an
example, Figure 5 shows the AAT2868 driving a single
white LED with up to 124mA by connecting D1-D4
together to the LED cathode.
Printed Circuit Board
Layout Recommendations
When designing a PCB for the AAT2868, the key requirements are:
1. Place the flying capacitors C1 and C2 as close to the
chip as possible; otherwise 1.5x mode performance
will be compromised.
2. Place input and output decoupling capacitors as close
to the chip as possible to reduce switching noise and
output ripple.
3. Connect the exposed pad to GND plane to get best
power dissipation.
Part Number
Value (µF)
Voltage
Temp. Co.
ESR (mΩ)
at 1MHz
Case
GRM188R61C105KA93
GRM185R60J105KE21
GRM188R61A225KE34
C1608X5R1C105K
C1608X5R0J225K
1
1
2.2
1
2.2
16
6.3
10
16
6.3
X5R
X5R
X5R
X5R
X5R
18
16
12
5.5
3.3
0603
0603
0603
0603
0603
Table 6: AAT2868 Recommended Capacitors.
18
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DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
C1+
C1
1µF
VIN
2.7~5.5V
C2+
C2
1µF
C1C2IN
OUTCP
INLDO
CIN
2.2µF
COUT
1µF
AAT2868
PWM
PWM
LDOA
LDOA
LDOB
AGND
FCAP
CF
56nF
GND
Up to
124mA
D1
D2
D3
D4
EN/SET
AS2Cwire
D1
LDOB
CLDOB
2.2µF
CLDOA
2.2µF
Figure 5: Higher Current, Single LED Application.
Schematic and Layout
U1
AAT2868
C1
1µF
J1
1
18
7
6
DC+
V_LDO
CIN
2.2µF
DC-
8
5
AAT2868
White LED
Driver
R1
0
D1
FCAP
CF
56nF
EP
D1
D2
D3
D4
LDOA
LDOB
R2
0
R3
0
R4
0
D3
D2
10
11
12
13
3
D4
LDOA
2
LDOB
CLDOB
2.2µF
PWM
CLDOA
2.2µF
EN/SET
R10 R11 R12
1k 1k 1k
SELECT
R7
50k
VOUT
COUT
1µF
EN/SET
PWM
9
R8
50k
C2
1µF
16
15
17
GND
AGND
14
4
V _MCU
C2+
C2OUTCP
C1+
C1IN
INLDO
1
2
3
4
U2
VDD
GP5
GP4
GP3
PIC12F675
VSS
GP0
GP1
GP2
C3
0.1µF
8
7
6
5
R9
1k
LED2
Red
R6
1k
DETAIL
LED1
SEND
AS2Cwire
Microcontroller
Figure 6: AAT2868 Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
19
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Figure 7: AAT2868 Evaluation Board Top Side Layout.
Figure 8: AAT2868 Evaluation Board
Bottom Side Layout.
Component
Part Number
Description
Manufacturer
U1
U2
R1, R2, R3, R4
R7, R8
R6, R9, R10, R11, R12
C1, C2, COUT
CIN, CLA, CLB
C3
CF
D1, D2, D3, D4
LED1
LED2
CYCLE, UP, DOWN
AAT2868IDT-T1
PIC12F675
RC0603FR-070RL
RC0603FR-0749K9L
RC0603FR-071KL
GRM188R71C105K
GRM188R61A225K
GRM188R71C104K
GRM188R71C563K
RS-0805UW
0805KGCT
0805KRCT
6*6*5
High Efficiency, 4 Channel, 1X/1.5X Charge Pump for White LED
8-Pin Flash-Based 8-Bit CMOS Microcontroller
Res 0Ω 1/10W 1% 0603 SMD
Res 49.9KΩ 1/10W 1% 0603 SMD
Res 1KΩ 1/10W 1% 0603 SMD
Cap Ceramic 1μF 0603 X7R 16V 10%
Cap Ceramic 2.2μF 0603 X5R 10V 10%
Cap Ceramic 0.1μF 0603 X7R 16V 10%
Cap Ceramic 0.056μF 0603 X7R 16V 10%
20mA White LED 0805
Green LED 0805
Red LED 0805
12V 50mA Pushbutton
Skyworks
Microchip
Table 8: AAT2868IDT-DB1 Evaluation Board Bill of Materials.
20
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
Yageo
Murata
Realstar
HB
HB
E-LT
DATA SHEET
AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TQFN 3.0 x 2.2-18L
5CXXY
AAT2868IDT-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
TQFN3.0 x 2.2-183
Index Area
Pin 1 Indicator
(optional)
0.40 BSC
0.20 ± 0.05
0.203 REF
0.75 ± 0.05
3.00 ± 0.05
1.90 ± 0.05
0.30 ± 0.05
0.05 ± 0.05
Side View
2.20 ± 0.05
Top View
1.10 ± 0.05
Bottom View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3.The leadless package family, which includes QFN, TQFN, DFN, TDFN, and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202072B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
21