AAT AAT2805 Dual high efficiency charge pump for white led and flash application Datasheet

AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
General Description
Features
The AAT2805 is a dual charge pump designed to
support both the white LED backlight and flash applications for systems operating with lithium-ion/polymer batteries. The backlight charge pump is capable
of driving up to four LEDs at a total of 120mA. The
current sinks may be operated individually or in parallel for driving higher current LEDs. To maximize
power efficiency, the charge pump operates in 1X,
1.5X, or 2X mode, where the mode of operation is
automatically selected by comparing the forward
voltage of each LED with the input voltage.
AnalogicTech's AS2Cwire™ (Advanced Simple Serial
Control™) serial digital input is used to enable, disable, and set current for each LED with a 16-level
logarithmic scale plus four low-current settings down
to 50µA for optimized efficiency, with a typical operating quiescent current of less than 50µA.
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•
•
•
•
•
•
•
•
The flash charge pump is a charge pump doubler
with a regulated output voltage. It is designed to
deliver 120mA of continuous current and up to
250mA of pulsed current. It has an independent
enable pin for improved power savings.
ChargePump™
VIN Range: 2.7V to 5.5V
Dual Charge Pump to Support Backlight and
Flash LEDs
Backlight Charge Pump:
— Regulated Current
— Four Current Sink Inputs
— AS2Cwire Brightness Control
— Tri-Mode Charge Pump
— Maximum 30mA of Current Per Input
— Low IQ (50µA) in Light Load Mode
Flash Charge Pump:
— Regulated Output Voltage
— Up to 250mA of Pulsed Current
Independent Backlight/Flash Control
Low Noise 1MHz Constant Frequency
Operation
Automatic Soft-Start
No Inductors
Available in TDFN44-16 Package
Applications
The AAT2805 has thermal protection and built-in
soft-start circuitry. A low-current shutdown feature
disconnects the load from VIN and reduces quiescent
current to less than 1µA.
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•
•
The AAT2805 is available in a Pb-free, space-saving,
thermally-enhanced TDFN44-16 package and is
rated over the -40°C to +85°C temperature range.
Color (RGB) Lighting
White LED Backlighting
White LED Photo Flash
Typical Application
C1
1μF
C2
1μF
C3
1μF
C1+ C1- C2+ C2- C3+ C3-
VOUT_FLASH
VOUT_FL
COUT
1μF
VIN
VIN
AAT2805
CIN
1μF
Backlight
VOUT_BL
D1
EN/SET
EN_FLSH
D2
D3
D4
EN/SET
EN_FLSH
GND
2805.2006.04.1.7
Flash
D1
D2
D3
D4
COUT
1μF
1
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Pin Descriptions
Pin #
Symbol
1
2
C3C3+
3
VOUT_FL
4
5
6
7
8
9
VIN
D4
D3
D2
D1
GND
10
EN/SET
11
12
13
C1+
C1VOUT_BL
14
15
16
EP
C2+
C2EN_FLSH
Function
Flying capacitor 3 negative terminal.
Flying capacitor 3 positive terminal. Connect a 1µF capacitor between C3+ and C3-.
Regulated output voltage for flash LED. Requires 1µF capacitor connected between this
pin and ground.
Input power supply. Requires 1µF capacitor connected between this pin and ground.
Current sink input 4.
Current sink input 3.
Current sink input 2.
Current sink input 1.
Ground.
AS2Cwire serial interface control pin. It is used to enable/disable the backlight charge
pump and to control the brightness of the white LEDs.
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
Flying capacitor 1 negative terminal.
Regulated output voltage for white LED. Requires 1µF capacitor connected between this
pin and ground.
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-.
Flying capacitor 2 negative terminal.
Enable/disable pin for the flash charge pump.
Exposed paddle (bottom); connect to GND directly beneath package.
Pin Configuration
TDFN44-16
(Top View)
C3C3+
VOUT_FL
VIN
D4
D3
D2
D1
2
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
EN_FLSH
C2C2+
VOUT_BL
C1C1+
EN/SET
GND
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Absolute Maximum Ratings1
Symbol
VIN
VEN/SET; EN_FL
TLEAD
Description
Input Voltage
EN/SET; EN_FL to GND Voltage
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to VIN + 0.3
300
V
V
°C
Value
Units
2.0
50
W
°C/W
Thermal Information2
Symbol
PD
θJA
Description
Maximum Power Dissipation
Maximum Thermal Resistance
3
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. Derate 6.25mW/°C above 25°C.
2805.2006.04.1.7
3
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Electrical Characteristics1
VIN = 3.6V; CIN = COUT = C1 = C2 = C3 = 1.0µF; TA = -40°C to +85°C, unless otherwise noted.
Typical values are TA = 25°C.
Symbol
Description
Conditions
Min Typ Max Units
Input Power Supply
VIN
ICC
ISHDN
IDX
I(D-Match)
RSINK
VOUT_FL
IOUT_FL
TSS
FCLK
VEN(L)
VEN(H)
TEN/SET LO
TEN/SET_HI_MIN
TEN/SET_HI_MAX
TOFF
TLAT
II
Operation Range
Operating Current
2.7
1X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
Current; EN_FLSH = GND, EN/SET = VIN
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
Current; EN_FLSH = GND, EN/SET = VIN
2X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
Current; EN_FLSH = GND, EN/SET = VIN
EN_FLSH = GND, 50µA Output Setting,
1X Mode
3.0 ≤ VIN ≤ 5.5, No Load Current;
EN_FLSH = VIN, EN/SET = GND
EN_FLSH = EN/SET = 0
ISET = 30mA; TA = 25°C
Shutdown Current
Input Current Accuracy2, 3
Current Matching Between
VD1:D4 = 3.6, VIN = 3.5V
Any Two Current Sink Inputs2, 4
Sink Switch Impedance (each)2
3.0V < VIN < 5V, IOUT = 100mA;
Flash Charge Pump Output
EN_FLSH = VIN
3.0V < VIN < 5V, IOUT = 150mA;
Voltage5
EN_FLSH = VIN
Maximum Continuous IOUT5
VIN = 3.6V; VOUT = 4.5V; EN_FLSH = VIN
Maximum Pulsed IOUT5
VIN = 3.6V; VOUT = 4.5V; IPULSED < 500ms
Soft-Start Time
Clock Frequency
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
VEN/SET < 0.6V
Minimum EN/SET High Time
VEN/SET > 1.4V
Maximum EN/SET High Time
EN/SET Off Timeout6
VEN/SET < 0.6V
EN/SET Latch Timeout7
VEN/SET > 1.4V
Enable and EN/SET Input
VEN/SET = VEN_FLSH = VIN
Leakage
0.3
5.5
1
1.0
3.0
1.0
3.0
50
2.0
-10
mA
µA
4.5
mA
1.0
10
µA
%
0.5
%
Ω
4.32
7
4.5
4.68
4.3
4.5
4.7
120
250
V
mA
100
1.0
75
500
500
µs
MHz
V
V
µs
ns
µs
µs
µs
1.0
µA
0.4
1.4
0.3
75
50
-1.0
V
1. The AAT2805 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. Specification applies only to the tri-mode charge pump.
3. Determined by the average of all active channels.
4. Current matching is defined as the deviation of any sink current from the average of all active channels.
5. Specification applies only to the charge pump doubler.
6. The EN/SET pin must remain logic low (less than VEN(L)) for the duration of longer than 500µs to guarantee the off timeout.
7. The EN/SET pin must remain logic high (greater than VEN(H)) for the duration of longer than 500µs to guarantee the latch timeout.
4
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–Flash Driver Charge Pump Section
Output Voltage vs. Output Current
Maximum Current Pulse vs. Supply Voltage
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
Output Voltage (V)
4.60
4.56
4.52
4.48
3.6V
3.0V
3.3V
4.44
2.7V
4.40
0.1
1.0
10.0
100.0
1000.0
Maximum Current Pulse (mA)
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
450
400
One-shot pulse duration = 250ms
VOUT > 4.0V
350
300
250
200
150
100
50
0
3.0
3.1
Output Current (mA)
3.2
3.3
3.4
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Supply Voltage (V)
Start-Up Time
Start-Up Time
(50mA Load)
(100mA Load)
EN_FLSH
(1V/div)
EN_FLSH
(1V/div)
VOUT_FL
(1V/div)
VOUT_FL
(1V/div)
TIme (100µs/div)
TIme (100µs/div)
Load Response vs. Time
Load Response vs. Time
(50mA Load)
(100mA Load)
VIN = 3.5V
VIN = 3.5V
VOUT_FL
(10mV/div)
VOUT_FL
(10mV/div)
IOUT
(20mA/div)
IOUT
(50mA/div)
Time (5ms/div)
2805.2006.04.1.7
3.5
Time (5ms/div)
5
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–Flash Driver Charge Pump Section
Output Ripple Voltage vs. Time
Output Ripple Voltage vs. Time
(IOUT = 50mA @ VIN = 3.5V)
(IOUT = 100mA @ VIN = 3.5V)
VIN
(10mV/div)
VIN
(10mV/div)
VOUT
(10mV/div)
VOUT
(20mV/div)
IIN
(10mA/div)
IIN
(10mA/div)
Time (500ns/div)
Time (500ns/div)
Supply Current (mA)
3.00
2.75
2.50
IOUT = 0μA
C3 = 1μF
VEN_FL = VIN
2.25
2.00
1.75
1.50
1.25
1.00
2.5
3.0
3.5
4.0
Supply Voltage (V)
6
Oscillator Frequency vs. Supply Voltage
Oscillator Frequency (MHz)
Supply Current vs. Supply Voltage
4.5
5.0
1.30
1.25
+25°C
1.20
1.15
+85°C
-40°C
1.10
2.7
3.2
3.7
4.2
4.7
Supply Voltage (V)
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
Turn-On to 1X Mode
Turn-On to 1.5X Mode
(VIN = 4.2V; 20mA Load)
(VIN = 3.5V; 20mA Load)
EN
(2V/div)
EN
(2V/div)
CP
(2V/div)
CP
(2V/div)
VSINK
(500mV/div)
VSINK
(500mV/div)
IIN
(200mA/div)
IIN
(200mA/div)
Time (100µs/div)
Time (100µs/div)
Turn-On to 2X Mode
Turn-Off from 1.5X Mode
(VIN = 2.8V; 20mA Load)
(VIN = 3.5V; 20mA Load)
EN
(2V/div)
EN
(2V/div)
CP
(2V/div)
VF
(1V/div)
VSINK
(500mV/div)
IIN
(100mA/div)
IIN
(200mA/div)
Time (100µs/div)
Time (500µs/div)
Current Matching vs. Temperature
Efficiency vs. Supply Voltage
100
20.4
4.1mA
VF = 2.9V
Efficiency (%)
80
70
60
50
40
10.2mA
VF = 3.1V
1mA
VF = 2.7V
30
Channel 2
20.2
Current (mA)
90
20mA
VF = 3.4V
20
20.0
Channel 4
19.8
Channel 3
19.6
Channel 1
19.4
19.2
10
19.0
0
2.6
2.8
2.9
3.1
3.2
3.4
3.6
3.7
Supply Voltage (V)
2805.2006.04.1.7
3.9
4.0
4.2
-40
-20
0
20
40
60
80
Temperature (°°C)
7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
Load Characteristics
Load Characteristics
(VIN = 3.7V; 1.5X Mode; 15mA Load)
(VIN = 2.7V; 2X Mode; 15mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
Time (500ns/div)
Time (500ns/div)
Load Characteristics
Load Characteristics
(VIN = 3.9V; 1.5X Mode; 20mA Load)
(VIN = 2.9V; 2X Mode; 20mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
Time (500ns/div)
Load Characteristics
Load Characteristics
(VIN = 4.2V; 1.5X Mode; 30mA Load)
(VIN = 3.2V; 2X Mode; 30mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
Time (500ns/div)
8
Time (500ns/div)
Time (500ns/div)
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
400
350
300
250
-40°C
200
150
25°C
100
85°C
50
0
350
300
-40°C
250
200
150
25°C
100
85°C
50
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Input Voltage (V)
Input Voltage (V)
Input Ripple vs. Input Voltage
Enable Threshold High vs. Input Voltage
Enable Threshold High (V)
18
16
Amplitude (mV)
EN/SET Off Timeout vs. Input Voltage
EN/SET Off Timeout (μ
μs)
EN/SET Latch Timeout (μ
μs)
EN/SET Latch Timeout vs. Input Voltage
14
12
20mA
10
30mA
8
6
4
10.2mA
2
0
2.50
2.67
2.84
3.01
3.18
3.35
3.52
3.69
3.86
4.03
4.20
Input Voltage (V)
1.2
1.1
1
0.9
-40°C
0.8
0.7
0.6
25°C
85°C
0.5
0.4
0.3
0.2
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Input Voltage (V)
Enable Threshold Low (V)
Enable Threshold Low vs. Input Voltage
1.2
1.1
1
0.9
-40°C
0.8
0.7
0.6
25°C
0.5
85°C
0.4
0.3
0.2
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Input Voltage (V)
2805.2006.04.1.7
9
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Functional Block Diagram
C3+
C3-
Soft-Start
2X Charge
Pump
EN_FLSH
1MHz
Oscillator
VOUT_FLSH
VIN
VREF
C1+
Soft-Start
Control
C1-
1X
1.5X
2X
Charge
Pump
1MHz
Oscillator
C2+
C2-
Voltage
Reference
VOUT_BL
6 X 16 Bit
ROM
EN/SET
Control
Logic
6 X 16 Bit
ROM
D/A
D1
D/A
D2
D/A
D3
D/A
D4
GND
Functional Description
The AAT2805 is a dual charge pump designed for
flash and white LED applications. The backlight
charge pump is a tri-mode load switch (1X) and high
efficiency (1.5X or 2X) charge pump device. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and
charge pump modes based on the input battery voltage and the current sink input voltage. As the battery
voltage discharges over time, the white LED charge
pump is enabled when any of the four current sink
inputs near dropout. The charge pump initially starts
in 1.5X mode. If the charge pump output drops
10
enough for any current source output to become
close to dropout, the charge pump will automatically
transition to 2X mode. The four constant current sink
inputs D1 to D4 can drive four individual LEDs with a
maximum current of 30mA per LED. The unused sink
inputs must be connected to VOUT_BL; otherwise, the
part will operate only in 2X charge pump mode. The
AS2Cwire serial interface enables and sets the constant current sink magnitudes. AS2Cwire addressing
allows the LED main channels D1-D3 to be controlled independently from the LED sub-channel D4.
The flash charge pump is a charge pump doubler
with regulated output voltage. It is designed to deliver 120mA of continuous current and 250mA of
pulsed current.
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
The AAT2805 requires six external components:
three 1µF ceramic capacitors for the charge pump
flying capacitors (C1, C2, and C3), one 1µF ceramic
input capacitor (CIN), one 0.33µF to 1µF ceramic
capacitor for backlight charge pump output capacitor
(COUT), and one 1µF ceramic capacitor for flash
charge pump output capacitor (COUT).
Constant Current Output Level Settings
The constant current level for the LED channels is set
via the AS2Cwire serial interface according to a logarithmic scale. The current level spacing is 1dB
between adjacent constant current settings. In this
manner, LED brightness appears to change linearly
when the settings are traversed. Because the inputs
D1 to D4 are true independent constant current
sinks, the voltage observed on any single given input
will be determined by the difference between VOUT
and the actual forward voltage (VF) of the LED being
driven.
Since the constant current levels are programmable,
no PWM (pulse width modulation) or additional control circuitry is needed to control LED brightness.
This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display
brightness, allowing the user to "set it and forget it."
With its high-speed serial interface (>1MHz data
rate), the LED current drive can be changed successively to brighten or dim LEDs, in smooth transitions (e.g., to fade-out) or in abrupt steps, giving the
user complete programmability and real-time control
of LED brightness.
For each Max Current scale (see Table 1), there are
16 current level settings separated from one another
by approximately 1dB. Code 1 is full-scale current
and Code 15 is full-scale current attenuated by
roughly 14dB. Code 16 is reserved as a "no current"
setting. When programming the charge pump, it will
default to the 20mA maximum scale.
The AAT2805 offers an additional Low Current mode
with reduced quiescent current (see Table 2). This
mode is especially useful for low-current applications
where a continuous, low-current state is maintained.
The reduction in quiescent current significantly
reduces the impact due to maintaining a continuous
backlighting state.
2805.2006.04.1.7
Data
20mA
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
7.9
7.0
6.3
5.7
5.1
4.4
4.1
0.0
Max IOUT (mA)
30mA
15mA
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
8.6
7.6
6.7
6.2
0.0
15.0
13.3
11.9
10.7
9.5
8.3
7.6
6.7
6.0
5.2
4.8
4.3
3.8
3.3
3.1
0.0
Table 1: Constant Current Programming Levels.
Data
D1-D3 (mA)
D4 (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0
0
0
0
0
0
0
0.05
0.5
1
2
0.05
0.5
1
2
0
0
0
0
0.05
0.5
1
2
0
0
0
0
0.05
0.5
1
2
Table 2: Low Current Register Settings.
11
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
AS2Cwire Serial Interface
The AS Cwire single wire interface is used to set the
possible combinations of current levels and LED
channel states. AS2Cwire has addressing capability
for multiple data registers. With multiple data registers, the main and sub-channel can be programmed
together or independently from one another.
AS2Cwire relies on the number of rising edges of the
EN/SET pin to address and load the registers.
AS2Cwire latches data or address after the EN/SET
pin has been held high for time TLAT. Address or data
is differentiated by the number of EN/SET rising
edges. Since the data registers are 4 bits each, the
differentiating number of pulses is 24 or 16, so that
Address 1 is signified by 17 rising edges, Address 2
by 18 rising edges, and so forth. Data is set to any
number of rising edges between 1 and including 16.
A typical write protocol is a burst of EN/SET rising
edges, signifying a particular address, followed by a
pause with EN/SET held high for the TLAT timeout
period, a burst of rising edges signifying data, and a
TLAT timeout for the data registers. Once an address
is set, then multiple writes to the corresponding data
register are allowed.
2
When EN/SET is held low for an amount of time
greater than TOFF, the charge pump enters into shutdown mode and draws less than 1µA from the supply. Address 1 is the default address on the first rising edge after the charge pump has been disabled.
Whenever shutdown mode is entered, all registers
are reset to 1.
AS2Cwire Addressing
Five addresses are available to enable all of the
part's functionality (see Table 3). Two 4-bit registers
control the main and sub-channel, giving 16 settings
for each. The main and sub-channel are programmed to the same constant current level by using
Address 1. Use Addresses 2 and 3 to program the
main and sub-channel independently. Use Address 4
to program the Max Current register, which sets the
Max Current scale. Lastly, Address 5 programs the
Low Current register. The Low Current register controls the efficient Low Current mode.
When the Max Current register is programmed to 1,
2, or 3, changing the data for Addresses 1-3 will
result in the corresponding values found in Table 1.
When the Max Current register is programmed to 4,
12
the part is programmed to operate in Low Current
mode and the Data for Addresses 1-3 is irrelevant. In
Low Current mode, the Low Current register takes
precedence. See the Low Current Register Settings
table below for the current level settings and main/
sub-configurations that result.
Address
EN/SET
Edges
Addressed
Register
1
2
3
4
5
17
18
19
20
21
1&2: D1-D4 Current
1: D1-D3 Current
2: D4 Current
3: Max Current
4: Low Current
Table 3: Address Settings.
Max Current and Low Current Registers
Use the Max Current and Low Current registers to
program constant current settings outside of the
20mA Max scale. By default (without changing the
Max Current register), the charge pump operates in
the 20mA Max scale (see Table 1). For example, to
change to the 30mA Max scale, address the Max
Current register with 20 rising edges and pause for
TLAT. Program the Max Current register with 2 rising
edges and pause for TLAT. The part will next operate
in the same Data row, but for the setting found in the
30mA Max column. Next, to change to a different
setting on the 30mA Max scale, address the D1-D4
register with 17 rising edges. Program the new constant current level with 1-16 rising edges. The part will
update to the new Data setting as shown in Table 1.
The charge pump has a distinct Low Current mode
with ultra-low quiescent current. For drive currents of
2mA or less, the part operates with significantly
reduced quiescent current. This is particularly useful
for applications requiring an "always on" condition
such as transmissive displays. For another example,
to change to Low Current mode, address the Max
Current register with 20 rising edges and pause for
TLAT. Program the Max Current register with 4 rising
edges and pause for TLAT. Address the Low Current
register with 21 rising edges and pause for TLAT.
Program the Low Current register with 1-16 rising
edges. The part will update to the new Low Current
mode setting and operate with significantly reduced
quiescent current.
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
AS2Cwire Serial Interface Timing Diagram
Address
Data
THI
TLO
TLAT
TLAT
EN/SET
1
2
Address
17
18
2...
0
0
Data Reg 2
0
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
Table 4: Maximum Current Settings Address 4.
Disabled Current Sinks
The backlight charge pump is equipped with an autodisable feature to protect against an LED failure condition. Current sink inputs that are not used should
be disabled. To disable and properly terminate
unused current sink inputs, they must be tied to VOUT.
If left unconnected or terminated to ground, the part
will be forced to operate in 2X charge pump mode.
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from
activating prematurely. When properly terminated,
only a small sense current flows for each disabled
channel. The sense current for each disabled channel is less than 120µA.
n <= 16
1
Data Reg 1
Data
2805.2006.04.1.7
1
n
Applications Information
LED Selection
The AAT2805 is specifically intended for driving white
LEDs. However, the device design will allow the
AAT2805 to drive most types of LEDs with forward
voltage specifications ranging from 2.0V to 4.3V.
LED applications may include main display backlighting, camera photo-flash applications, color
(RGB) LEDs, infrared (IR) diodes for remotes, and
other loads benefiting from a controlled output current generated from a varying input voltage. Since
the D1 to D4 input current sinks are matched with
negligible voltage dependence, the LED brightness
will be matched regardless of the specific LED forward voltage (VF) levels.
In some instances (e.g., in high-luminous-output
applications such as photo flash), it may be necessary to drive high-VF type LEDs. The low dropout current sinks in the AAT2805 make it capable of driving
LEDs with forward voltages as high as 4.3V at full
current from an input supply as low as 3.0V. Outputs
can be paralleled to drive high-current LEDs without
complication.
13
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Device Switching Noise Performance
Ceramic Capacitor Materials
The AAT2805 operates at a fixed frequency of
approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication
devices. Back-injected noise appearing on the input
pin of the charge pump is 20mV peak-to-peak, typically ten times less than inductor-based DC/DC
boost converter white LED backlight solutions. The
AAT2805 soft-start feature prevents noise transient
effects associated with inrush currents during startup of the charge pump circuit.
Ceramic capacitors less than 0.1µF are typically
made from NPO or C0G materials. NPO and C0G
materials generally have tight tolerance and are
very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or
Y5V dielectric materials. Large ceramic capacitors
(i.e., greater than 2.2µF) are often available in lowcost Y5V and Z5U dielectrics, but capacitors
greater than 1µF are not typically required for
AAT2805 applications.
Capacitor Selection
Careful selection of the six external capacitors CIN,
C1, C2, C3 and COUT (for backlight and flash) is important because they will affect turn-on time, output ripple, and transient performance. Optimum performance will be obtained when low equivalent series
resistance (ESR) (<100mΩ) ceramic capacitors are
used. In general, low ESR may be defined as less
than 100mΩ. A value of 1µF for all six capacitors is
a good starting point when choosing capacitors.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with
the AAT2805. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic
counterparts. A ceramic capacitor typically has very
low ESR, is lowest cost, has a smaller PCB footprint,
and is non-polarized. Low ESR ceramic capacitors
help maximize charge pump transient response.
Since ceramic capacitors are non-polarized, they are
not prone to incorrect connection damage.
Equivalent Series Resistance
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal to
a capacitor that is caused by the leads, internal connections, size or area, material composition, and
ambient temperature. Capacitor ESR is typically
measured in milliohms for ceramic capacitors and
can range to more than several ohms for tantalum or
aluminum electrolytic capacitors.
14
Capacitor area is another contributor to ESR.
Capacitors that are physically large will have a lower
ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit transient response when compared to an equal
value capacitor in a smaller package size.
Thermal Protection
The AAT2805 has a thermal protection circuit that
will shut down the two charge pumps if the die temperature rises above the thermal limit.
Charge Pump Power Efficiency
Backlight Charge Pump: The charge pump efficiency discussion in the following sections only
accounts for the efficiency of the charge pump section itself. Due to the unique circuit architecture, it
is very difficult to measure efficiency in terms of a
percent value comparing input power over output
power. Since the outputs are pure constant current
sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (D1 to D4) to derive an overall output power
measurement. For any given application, white
LED forward voltage levels can differ, yet the output drive current will be maintained as a constant.
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
total device efficiency is to observe the total input
power to the device for a given LED current drive
level. The best white LED driver for a given application should be based on trade-offs of size, external
component count, reliability, operating range, and
total energy usage...not just "% efficiency."
2805.2006.04.1.7
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Efficiency of the AAT2805 may be quantified under
very specific conditions and is dependent upon the
input voltage versus the output voltage seen across
the loads applied to outputs D1 through D4 for a given
constant current setting. Depending on the combination of VIN and voltages sensed at the current sinks,
the device will operate in load switch mode. When
any one of the voltages sensed at the current sinks
nears dropout, the device will operate in 1.5X or 2X
charge pump mode. Each of these modes will yield
different efficiency values. Refer to the following two
sections for explanations for each operational mode.
Load Switch Mode Efficiency: The load switch
mode is operational at all times and functions alone
to enhance device power conversion efficiency when
VIN is greater than the voltage across the load. When
in load switch mode, the voltage conversion efficiency is defined as output power divided by input power:
η=
POUT
PIN
The expression to define the ideal efficiency (η) can
be rewritten as:
η=
POUT VOUT × IOUT VOUT
=
=
PIN
VIN × IOUT
VIN
In addition, with an ideal 1.5X charge pump, the output current may be expressed as 2/3 of the input current. The expression to define the ideal efficiency (η)
can be rewritten as:
η=
-or-
η(%) = 100
Flash Charge Pump: The flash charge pump is a
regulated output voltage doubling charge pump. The
efficiency is defined as a linear voltage regulator with
an effective output voltage that is equal to two times
the input voltage. The expression to define the ideal
efficiency can be written as:
η=
⎛ VOUT ⎞
⎝ VIN ⎠
Charge Pump Mode Efficiency: Fractional charge
pumps will boost the input supply voltage in the event
where VIN is less than the voltage required on the constant current source outputs. The efficiency (η) can be
simply defined as a linear voltage regulator with an
effective output voltage that is equal to one and a half
or two times the input voltage. Efficiency (η) for an
ideal 1.5X charge pump can typically be expressed
as the output power divided by the input power:
η=
2805.2006.04.1.7
POUT
PIN
⎛ VOUT ⎞
⎝ 1.5VIN⎠
For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 95%.
Due to internal switching losses and IC quiescent
current consumption, the actual efficiency can be
measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA.
Efficiency will decrease as load current drops below
0.05mA or when level of VIN approaches VOUT.
-or-
η(%) = 100
VOUT × IOUT
VOUT
POUT
=
=
PIN
VIN × 1.5IOUT 1.5VIN
POUT
VOUT × IOUT
VOUT
=
=
PIN
VIN × 2.0IOUT 2.0VIN
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ 2.0VIN⎠
For a charge pump with an output of 5V and a nominal input of 3V, the theoretical efficiency is 83.3%.
Due to internal switching losses and IC quiescent
current consumption, the actual efficiency can be
measured at approximately 82%. Efficiency will
decrease as the level of VIN approaches that of the
regulated VOUT. Refer to the device typical characteristics curves for expected actual efficiency
based on either input voltage or load current.
15
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN44-16
NIXYY
AAT2805IXN-4.5-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Package Information
TDFN44-16
3.30 ± 0.05
Detail "B"
4.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10
0.375 ± 0.125
0.16
0.075 ± 0.075
0.1 REF
4.00 ± 0.05
2.60 ± 0.05
Top View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Bottom View
0.45 ± 0.05
Detail "A"
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
0.05 ± 0.05
Detail "B"
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights,
or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
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AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
16
2805.2006.04.1.7