Analogic AAT3156 High efficiency 1x/1.5x/2x charge pump for white led application Datasheet

AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
General Description
Features
The AAT3156 is a low noise, constant frequency
charge pump DC/DC converter that uses a trimode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency for
white LED applications. The AAT3156 is capable of
driving six-channel LEDs at a total of 180mA 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 VIN and VOUT) make this part ideally suited for
small battery-powered applications.
•
•
•
•
•
•
•
•
•
•
•
•
•
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 low housekeeping current of only 50µA.
Each output of the AAT3156 is equipped with builtin protection for VOUT short circuit and auto disable
for LED failure condition. Built-in soft-start circuitry
prevents excessive inrush current during start-up.
A low current shutdown feature disconnects the
load from VIN and reduces quiescent current to less
than 1µA.
ChargePump™
VIN Range: 2.7V to 5.5V
Fully Programmable Current with Single Wire
— 16-Step Logarithmic Scale
— 15/20/30mA Max Current
— Four Low Current Settings Down to 50µA
— Low IQ (50µA) for Low Current Mode
Tri-Mode 1X, 1.5X, and 2X Charge Pump for
Maximum Efficiency and VF Coverage
Drives Six Channels of LEDs
Individual Main/Sub-Group Control
No Inductors, Low Noise Operation
1MHz Constant Switching Frequency
Small Application Circuit
Built-In Thermal Protection
Built-In Auto-Disable For Open Circuit
Automatic Soft-Start
IQ <1µA in Shutdown
Thermally-Enhanced QFN44-16 Package
Applications
•
•
•
•
The AAT3156 is available in a space-saving, thermally-enhanced 16-pin 4x4mm QFN package.
Color (RGB) Lighting
Programmable Current Sinks
White LED Backlighting
White Photo Flash for DSCs
Typical Application
VIN
2.7V to 5.5V
C1+
C1
1µF
CIN
1µF
C1C2+
C2
1µF
AAT3156
C2VOUT
D1
D2
D3
D4
D5
D6
COUT
1µF
EN/SET
D1
EN/SET
D2
D3
D4
D5
GND
3156.2005.06.1.1
D6
1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Pin Descriptions
Pin #
Symbol
1
D6
2
EN/SET
3
N/C
4
VOUT
Charge pump output to drive load circuit. Requires 1µF capacitor connected between
this pin and ground.
5
C2+
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-.
6
C1+
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
7
C1-
Flying capacitor 1 negative terminal.
8
C2-
Flying capacitor 2 negative terminal.
9
GND
10
IN
11
GND
12
D1
Current sink input #1.
13
D2
Current sink input #2.
14
D3
Current sink input #3.
15
D4
Current sink input #4.
16
D5
Current sink input #5.
EP
Function
Current sink input #6.
AS2Cwire serial interface control pin.
No connection.
Ground.
Input power supply. Requires 1µF capacitor connected between this pin and ground.
Ground.
Exposed paddle (bottom); connect to GND directly beneath package.
Pin Configuration
QFN44-16
(Top View)
15
13
16
14
D4
1
12
D1
EN/SET
2
11
GND
N/C
3
10
IN
VOUT
4
9
GND
AAT3156
8
7
6
5
C2C1-
C1+
C2+
2
D2
D3
D5
D6
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Absolute Maximum Ratings1
Symbol
VIN
VEN/SET
IOUT 2
TJ
TLEAD
Description
Input Voltage
EN/SET to GND Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6
-0.3 to VIN + 0.3
180
-40 to 150
300
V
V
mA
°C
°C
Value
Units
2.0
50
W
°C/W
Thermal Information3
Symbol
PD
θJA
Description
4
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. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 6.25 mW/°C above 25°C.
3156.2005.06.1.1
3
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Electrical Characteristics1
CIN = COUT = C1 = C2 = 1.0µF; TA = -40°C to 85°C, unless otherwise noted.
Typical values are at TA = 25°C, VIN = 3.5V.
Symbol
Description
Conditions
Input Power Supply
VIN
Operation Range
ICC
ISHDN
IDX
I(D-Match)
Operating Current
Shutdown Current
ISINK Current Accuracy2
Current Matching Between Any
Two Current Sink Inputs3, 4
VTH
1X to 1.5X or 1.5X to 2X Transition
Threshold at Any ISINK Pin
Charge Pump Section
TSS
Soft-Start Time
FCLK
Clock Frequency
EN/SET
VEN(L)
Enable Threshold Low
VEN(H)
Enable Threshold High
TEN/SET LO
EN/SET Low Time
TEN/SET_HI_MIN Minimum EN/SET High Time
TEN/SET_HI_MAX Maximum EN/SET High Time
TOFF
EN/SET Off Timeout
TLAT
EN/SET Latch Timeout
IEN/SET
EN/SET Input Leakage
Min
Typ
Max
Units
5.5
1
V
0.3
1
3
2.0
3.7
2.7
1X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
2X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
50µA Setting, 1X Mode
EN/SET = 0
ISET = 30mA, TA = 25°C
ISET = 4.1mA, TA = 25°C
VF:D1:D4 = 3.6V
50
27
3.69
ISET = 20mA
VIN = 2.7V
VIN = 5.5V
30
4.1
0.5
1
33
4.51
µA
µA
mA
%
150
mV
100
1000
µs
kHz
0.4
1.4
0.3
75
50
-1
mA
75
500
500
1
V
V
µs
ns
µs
µs
µs
µA
1. The AAT3156 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 at IOUT = 20mA and 2mA.
4. Specification applies only to the tri-mode charge pump.
4
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
Efficiency vs. Supply Voltage
Turn-On to 1X Mode
(VIN = 4.2V; 20mA Load)
100
4.1mA
VF = 2.9V
10.2mA
VF = 3.1V
20mA
VF = 3.4V
EN
(2V/div)
Efficiency (%)
90
80
CP
(2V/div)
VSINK
(500mV/div)
70
60
IIN
(200mA/div)
50
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
100µ
µs/div
Supply Voltage (V)
Turn-On to 1.5X Mode
Turn-On to 2X Mode
(VIN = 3.8V; 20mA Load)
(VIN = 2.8V; 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)
100µ
µs/div
100µ
µs/div
Turn-Off from 1.5X Mode
Current Matching vs. Temperature
(VIN = 3.5V; 20mA Load)
20.2
Channel 1
Channel 2
EN
(2V/div)
Current (mA)
20.0
VF
(1V/div)
IIN
(100mA/div)
19.8
Channel 5
19.6
Channel 3
19.4
Channel 4
Channel 6
19.2
-40
100µ
µs/div
3156.2005.06.1.1
-20
0
20
40
60
80
Temperature (°°C)
5
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
Load Characteristics
Load Characteristics
(VIN = 3.8V; 1.5X Mode; 15mA Load)
(VIN = 2.9V; 2X Mode; 15mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
500ns/div
Load Characteristics
Load Characteristics
(VIN = 4.0V; 1.5X Mode; 20mA Load)
(VIN = 3.1V; 2X Mode; 20mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
500ns/div
Load Characteristics
Load Characteristics
(VIN = 4.3V; 1.5X Mode; 30mA Load)
(VIN = 3.6V; 2X Mode; 30mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
6
500ns/div
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
TLAT vs. VIN
TOFF vs. VIN
350
400
350
300
-40°C
-40°C
300
TOFF (µ
µs)
TLAT (µ
µs)
250
200
150
25°C
85°C
100
250
200
25°C
150
85°C
100
50
50
0
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
VIN (V)
VIN (V)
Input Ripple vs. VIN
VIH vs. VIN
1.2
25
1
-40°C
0.9
15
10
VIH (V)
Amplitude (mV)
1.1
30mA
20
20mA
0.7
25°C
0.6
85°C
0.5
10.2mA
5
0.8
0.4
0.3
0.2
0
2.50
2.67
2.84
3.01
3.18
3.35
3.52
3.69
3.86
4.03
4.20
VIN (V)
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
VIN (V)
VIL vs. VIN
1.2
1.1
1
-40°C
VIL (V)
0.9
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
VIN (V)
3156.2005.06.1.1
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AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
1X, 1.5X and 2X
Charge Pump
VIN
VOUT
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
6 x 16 bit
ROM
EN/SET
AS2Cwire
Interface
6 x 16 bit
ROM
D/A
D1
D/A
D2
D/A
D3
D/A
D4
D/A
D5
D/A
D6
GND
Functional Description
ceramic input capacitor (CIN), and one 0.33µF to
1µF ceramic charge pump output capacitor (COUT).
The AAT3156 is a tri-mode load switch (1X) and
high efficiency (1.5X or 2X) charge pump device
intended for white LED backlight applications. 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 discharges over time, the AAT3156
charge pump is enabled when any of the six current sinks near dropout. The charge pump initially
starts in 1.5X mode. If the charge pump output
drops enough for any current sink to become close
to dropout, the charge pump will automatically transition to 2X mode.
The AAT3156 constant current sinks can drive six
individual LEDs with a maximum current of 30mA
per channel. The AS2Cwire serial interface enables
the AAT3156 and sets the constant current sink
magnitudes. AS2Cwire addressing allows the LED
main channels D1-D4 to be controlled independently from the LED sub-channels D5-D6.
The AAT3156 requires only four external components: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
8
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. In this manner, LED brightness
appears linearly when the settings in the scale are
traversed. Because the inputs D1 to D6 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.
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Since the constant current levels for the AAT3156 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 of the AAT3156 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, there are 16 current
level settings separated from one another by
approximately 1dB (see Current Settings table).
Code 1 is full-scale current and Code 15 is full-scale
attenuated roughly 14dB. Code 16 is reserved as a
"no current" setting.
Constant Current Programming Levels (mA)1
Data
20mA Max
IOUT (mA)
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
2
30mA Max
IOUT (mA)
15mA Max
IOUT (mA)
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
AS2Cwire Serial Interface
The Advanced Simple Serial Control (AS2Cwire) 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 AAT3156
main and sub-channels 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.
When EN/SET is held low for an amount of time
greater than TOFF, the AAT3156 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 AAT3156 has been disabled.
Whenever shutdown mode is entered, all registers
are reset to 1.
1. There is an additional Low Current mode with currents down to 50µA. See the Low Current Register Settings section.
2. The device defaults to the 20mA Max scale. Use the Max Current Register to change the Max Scale.
3156.2005.06.1.1
9
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
AS2Cwire Serial Interface Timing
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
2
17
18
1
1
2...
n <= 16
2
Data Reg 1
1
Data Reg 2
1
n
AS2Cwire Addressing
Max Current and Low Current Registers
Five addresses are available to enable all of the
part's functionality. Two 4-bit registers control the
main and sub-channels, giving 16 settings for each.
The main and sub-channels are programmed to the
same constant current level by using Address 1.
Use Addresses 2 and 3 to program the main and
sub-channels 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 the Constant Current
Programming Levels table.
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 AAT3156 operates in the
20mA Max scale (see Constant Current Programming Levels). 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-D6 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 according to the Constant
Current Programming Levels table.
When the Max Current register is programmed to 4,
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.
10
Address
EN/SET
Edges
Addressed
Register
1
17
2
3
4
5
18
19
20
21
1&2: D1-D6
Current
1: D1-D4 Current
2: D5-D6 Current
3: Max Current
4: Low Current
The AAT3156 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. As an 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.
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Max Current Register Settings—Address 4
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode1
Low Current Register Settings—Address 5
Data
D1-D4 (mA)
D5-D6 (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
Disabled Current Sinks
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
prematurely activating. When properly terminated,
only a small sense current flows for each disabled
channel. The sense current for each disabled channel is less than 120µA.
The AAT3156 is also equipped with an "auto-disable"
feature to protect against an LED failure condition.
Thermal Protection
The AAT3156 has a built-in thermal protection circuit that will shut down the charge pump if the die
temperature rises above the thermal limit, as is the
case during a short circuit of the VOUT pin.
Applications Information
LED Selection
The AAT3156 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3156 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to
4.3V. LED applications may include main and subLCD 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 D6 constant 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 AAT3156 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.
Current sinks can be paralleled to drive high-current LEDs without complication.
Device Switching Noise Performance
The AAT3156 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-topeak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solutions. The AAT3156 soft-start feature prevents
noise transient effects associated with in-rush currents during start up of the charge pump circuit.
1. Low Current Mode requires the Max Current register to be set to Low Current Mode. Low Current Mode is unaffected by the settings
for Addresses 1-3.
3156.2005.06.1.1
11
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following sections only account for the efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3156, it is very
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT3156 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."
The AAT3156 efficiency 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. One
should refer to the following two sections for explanations for each operational mode.
η=
The expression to define the ideal efficiency (η)
can be rewritten as:
η=
η(%) = 100
⎛ VOUT ⎞
⎝ VIN ⎠
Charge Pump Section Efficiency
The AAT3156 contains a fractional charge pump that
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=
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:
Load Switch Mode Efficiency
12
POUT VOUT × IOUT VOUT
=
=
PIN
VIN × IOUT
VIN
-or-
η=
The AAT3156 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:
POUT
PIN
POUT
VOUT × IOUT
VOUT
=
=
PIN
VIN × 1.5IOUT 1.5VIN
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ 1.5VIN⎠
3156.2005.06.1.1
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Capacitor Selection
Equivalent Series Resistance
Careful selection of the four external capacitors
(CIN, C1, C2, and COUT) 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 capacitor value of 1µF for all four capacitors is a good
starting point when choosing capacitors. If the constant current sinks are only programmed for light
current levels, then the capacitor size may be
decreased.
ESR is an important characteristic to consider
when selecting a capacitor. ESR is a resistance
internal to a capacitor which 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.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT3156. 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 to maximize charge pump
transient response. Since ceramic capacitors are
non-polarized, they are not prone to incorrect connection damage.
3156.2005.06.1.1
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1µF are typically
made from NPO or C0G materials. NPO and C0G
materials typically have tight tolerance and are stable over temperature. Larger capacitor values are
typically composed of X7R, X5R, Z5U, or Y5V
dielectric materials. Large ceramic capacitors, typically greater than 2.2µF, are often available in lowcost Y5V and Z5U dielectrics, but capacitors
greater than 1µF are typically not required for
AAT3156 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.
13
AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Ordering Information
Package
Marking1
QFN44-16
NMXYY
Part Number (Tape and Reel)2
AAT3156ISN-T1
0.330 ± 0.050
Pin 1 Identification
13
16
0.650 BSC
1
R0.030Max
4
9
8
4.000 ± 0.050
2.400 ± 0.050
5
2.280 REF
Top View
0.0125 ± 0.0125
Bottom View
0.203 ± 0.025
0.900 ± 0.050
4.000 ± 0.050
Pin 1 Dot By Marking
0.450 ± 0.050
0.600 ± 0.050
Package Information
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
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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, and advise customers 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 warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
14
3156.2005.06.1.1