Analogic AAT2806IXN-4.5-T1 Dual high efficiency charge pump for white led and flash application Datasheet

AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
General Description
Features
The AAT2806 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 80mA. 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
S2Cwire™ (Simple Serial Control™) serial digital
input is used to enable, disable, and set current for
each LED with an eight-level logarithmic scale plus
four low-current settings down to 50µA for optimized
efficiency, with a typical operating quiescent current
of less than 50µA.
•
•
•
•
•
•
•
•
•
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
— S2Cwire Brightness Control
— Tri-Mode Charge Pump
— Maximum 20mA 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 AAT2806 has thermal protection and built-in softstart circuitry. A low-current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1µA.
•
•
•
Color (RGB) Lighting
White LED Backlighting
White LED Photo Flash
The AAT2806 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.
Typical Application
C1
1μF
C2
1μF
C3
1μF
C1+ C1- C2+ C2- C3+ C3-
VOUT_FLASH
VOUT_FL
COUT
1μF
VIN
VIN
AAT2806
CIN
1μF
Backlight
VOUT_BL
D1
EN/SET
EN_FLSH
D2
D3
D4
EN/SET
EN_FLSH
GND
2806.2007.09.1.9
Flash
D1
D2
D3
D4
COUT
1μF
1
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Pin Descriptions
Pin #
Symbol
Function
1
2
3
C3C3+
VOUT_FL
4
5
6
7
8
9
10
VIN
D4
D3
D2
D1
GND
EN/SET
11
12
13
C1+
C1VOUT_BL
14
15
16
EP
C2+
C2EN_FLSH
Flying capacitor 3 negative terminal.
Flying capacitor 3 positive terminal. Connect a 1µF capacitor between C3+ and C3-.
Regulated output voltage for the 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.
S2Cwire 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 the white LEDs. 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
2806.2007.09.1.9
AAT2806
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
3
Maximum Power Dissipation
Maximum Thermal Resistance
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.
2806.2007.09.1.9
3
AAT2806
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
2.7
1X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
0.3
Current; EN_FLSH = GND, EN/SET = VIN
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
1.0
Current; EN_FLSH = GND, EN/SET = VIN
2X Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load
Operating Current
2.0
Current; EN_FLSH = GND, EN/SET = VIN
EN_FLSH = GND, 50µA Output Setting,
50
1X Mode
3.0 ≤ VIN ≤ 5.5, No Load Current;
2.0
EN_FLSH = VIN, EN/SET = GND
Shutdown Current
EN_FLSH = EN/SET = 0
2, 3
Input Current Accuracy
ISET = 20mA and ISET = 4.1mA; TA = 25°C
-10
Current Matching Between Any VD1:D4 = 3.6V, VIN = 3.5V
0.5
Two Current Sink Inputs2, 4
Sink Switch Impedance (each)2
7
3.0V < VIN < 5V, IOUT = 100mA;
4.32 4.5
Flash Charge Pump Output
EN_FLSH = VIN
3.0V < VIN < 5V, IOUT = 150mA;
Voltage5
4.3 4.5
EN_FLSH = VIN
Maximum Continuous IOUT5
VIN = 3.6V; VOUT = 4.5V; EN_FLSH = VIN
120
Maximum Pulsed IOUT5
VIN = 3.6V; VOUT = 4.5V; IPULSED < 500ms
250
Soft-Start Time
100
Clock Frequency
1.0
Enable Threshold Low
Enable Threshold High
1.4
EN/SET Low Time
0.3
Minimum EN/SET High Time
50
Maximum EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
Enable and EN/SET Input
-1.0
Leakage
5.5
V
1
3.0
mA
3.7
µA
4.5
mA
1.0
10
µA
%
%
Ω
4.68
V
4.7
mA
75
500
500
µs
MHz
V
V
µs
ns
µs
µs
µs
1.0
µA
0.4
75
1. The AAT2806 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.
4
2806.2007.09.1.9
AAT2806
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
3.6V
4.52
4.48
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
3.5
3.6
3.7
3.8
3.9
4.0
4.1
Supply Voltage (V)
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)
Time (5ms/div)
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)
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4.2
Time (500ns/div)
5
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics– Flash Driver Charge Pump Section
Supply Current vs. Supply Voltage
Oscillator Frequency vs. Supply Voltage
2.75
2.50
Oscillator Frequency (MHz)
Supply Current (mA)
3.00
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
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)
2806.2007.09.1.9
AAT2806
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)
VSINK
(500mV/div)
CP
(2V/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)
VF
(1V/div)
CP
(2V/div)
VSINK
(500mV/div)
IIN
(100mA/div)
IIN
(200mA/div)
Time (100µs/div)
Time (500µs/div)
Efficiency vs. Supply Voltage
Current Matching vs. Temperature
100
20.4
20mA
VF = 3.4V
10mA
VF = 3.1V
Current (mA)
Efficiency (%)
Channel 2
20.2
90
80
70
60
20.0
Channel 4
19.8
Channel 3
Channel 1
19.6
19.4
19.2
19.0
50
2.8
3.0
3.2
3.4
3.6
Supply Voltage (V)
2806.2007.09.1.9
3.8
4.0
4.2
-40
-20
0
20
40
60
80
Temperature (°°C)
7
AAT2806
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; 14mA Load)
(VIN = 2.7V; 2X Mode; 14mA 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)
Time (500ns/div)
EN/SET Off Timeout vs. Input Voltage
8
400
350
300
250
-40°C
200
150
100
25°C
85°C
50
0
EN/SET Off Timeout (μ
μs)
EN/SET Latch Timeout (μ
μs)
EN/SET Latch Timeout vs. Input Voltage
350
300
-40°C
250
200
150
25°C
85°C
100
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)
2806.2007.09.1.9
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics– White LED Backlight Driver Section
Input Ripple vs. Input Voltage
Enable Threshold High vs. Input Voltage
Enable Threshold High (V)
18
Amplitude (mV)
16
14
12
20mA
10
8
6
4
10mA
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
-40°C
0.9
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
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)
2806.2007.09.1.9
9
AAT2806
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 AAT2806 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
10
inputs near dropout. The charge pump initially starts
in 1.5X mode. If the charge pump output drops
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 20mA per LED. The unused sink
inputs must be connected to VOUT_BL; otherwise, the
part will operate only in 2X charge pump mode. The
S2Cwire serial interface enables and sets the constant current sink magnitudes. S2Cwire addressing
allows the LED main channels D1 to D3 to be controlled independently from the LED sub-channel D4.
2806.2007.09.1.9
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
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.
The AAT2806 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 the backlight charge pump output
capacitor (COUT), and one 1µF ceramic capacitor
for the flash charge pump output capacitor (COUT).
Constant Current Output Level Settings
The constant current level for the LED channels is set
via the S2Cwire serial interface (see Table 1).
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 realtime control of LED brightness.
The AAT2806 offers an additional Low Current mode
with reduced quiescent current (Data 13 to 16). 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.
2806.2007.09.1.9
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
IOUT (mA)
D1-D3
Sub-Group D4
20
14
10
7
20
14
10
7
0
0
0
0
0.05
0.5
1
2
20
14
10
7
0
0
0
0
20
14
10
7
0.05
0.5
1
2
Table 1: Constant Current Programming Levels.
S2Cwire Serial Interface
The current sink input magnitude on the backlight
charge pump is controlled by AnalogicTech's
S2Cwire serial digital input. The interface relies on
the number of rising edges of the EN/SET pin to
address and load the registers. S2Cwire latches
data or address after the EN/SET pin has been
held high for time TLAT. The interface records rising
edges of the EN/SET pin and decodes them into 16
different states, as indicated in Table 1. There are
four brightness levels for the main or sub-display
group with the possibility of individually turning ON
or OFF each group. To further optimize power efficiency, the device also offers four low-current levels for dim LED operation (Data 13 to 16). During
this low-current mode, the internal supply current
reduces to only 50µA typical.
The counter can be clocked at speeds up to 1MHz,
such that intermediate states are not visible. The
first rising edge of EN/SET enables the IC and initially sets the output LED current to 20mA. Once
the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain
the device output current at the programmed level.
The device is disabled 500µs (TOFF) after the
EN/SET pin transitions to a logic low state.
11
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
S2Cwire Serial Interface Timing Diagram
T HI
TLO
TOFF
TLAT
EN/SET
1
Data Reg
2
n-1
n ≤ 16
0
Disabled Current Sinks
The backlight charge pump is equipped with an
auto-disable 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 10µA.
Applications Information
LED Selection
The AAT2806 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT2806 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.
12
n
0
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 AAT2806 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.
Device Switching Noise Performance
The AAT2806 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
AAT2806 soft-start feature prevents noise transient
effects associated with inrush currents during start-up
of the charge pump circuit.
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) 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.
2806.2007.09.1.9
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Capacitor Characteristics
Charge Pump Power Efficiency
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with
the AAT2806. 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.
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.
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.
Ceramic Capacitor Materials
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
AAT2806 applications.
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.
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
components count, reliability, operating range, and
total energy usage...not just "% efficiency."
Efficiency of the AAT2806 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:
Thermal Protection
The AAT2806 has a thermal protection circuit that
will shut down the two charge pumps if the die temperature rises above the thermal limit.
2806.2007.09.1.9
η=
POUT
PIN
13
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
The expression to define the ideal efficiency (η) can
be rewritten as:
η=
POUT VOUT × IOUT VOUT
=
=
PIN
VIN × IOUT
VIN
-or-
η(%) = 100
⎛ 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:
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 the level of VIN approaches VOUT.
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=
POUT
VOUT × IOUT
VOUT
=
=
PIN
VIN × 2.0IOUT 2.0VIN
-or-
η(%) = 100
η=
POUT
PIN
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=
VOUT × IOUT
VOUT
POUT
=
=
PIN
VIN × 1.5IOUT 1.5VIN
⎛ 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.
-or-
η(%) = 100
14
⎛ VOUT ⎞
⎝ 1.5VIN⎠
2806.2007.09.1.9
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN44-16
NPXYY
AAT2806IXN-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
Option B:
R0.30 (4x) max
Round corner
Side View
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2806.2007.09.1.9
15
AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
© 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. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent,
copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the
customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty.
Specific testing of all parameters of each device is not necessarily performed. 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.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737- 4600
Fax (408) 737- 4611
16
2806.2007.09.1.9
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