AAT3151 [ANALOGICTECH]
High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications; 高效率1X / 1.5X / 2X电荷泵白光LED应用
| 型号： | AAT3151 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications |
| 文件： | 总14页 (文件大小：418K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
™
ChargePump
General Description
Features
The AAT3151 is a low noise, constant frequency
charge pump DC/DC converter that uses a tri-
mode load switch (1X), fractional (1.5X), and dou-
bling (2X) conversion to maximize efficiency for
white LED applications. The AAT3151 is capable of
driving four white LEDs at a total of 120mA from a
2.7V to 5.5V input. The current sinks may be oper-
ated individually or in parallel for driving higher-cur-
rent LEDs. A low external parts count (two 1µF fly-
ing capacitors and two small 1µF capacitors at VIN
and VOUT) makes the AAT3151 ideally suited for
small battery-powered applications.
•
•
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 Four 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 Short-Circuit
Automatic Soft Start
IQ <1µA in Shutdown
TDFN33-12 Package
•
•
•
•
•
•
•
•
•
•
•
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.
The charge pump output of the AAT3151 is
equipped with built-in protection for VOUT. Each
current sink input has short-circuit and auto-disable
to guard against LED failure conditions. Built-in
soft-start circuitry prevents excessive inrush cur-
rent during start-up. A low-current shutdown fea-
ture disconnects the load from VIN and reduces
quiescent current to less than 1µA.
Applications
•
•
•
•
Color (RGB) Lighting
Programmable Current Sinks
White LED Backlighting
White Photo Flash for Digital Still Cameras
The AAT3151 is available in a Pb-free, space-saving,
thermally-enhanced, 12-pin 3x3mm TDFN package.
Typical Application
VIN
2.7V to 5.5V
C1+
C1
1µF
C
IN
1µF
C1-
C2+
C2
1µF
AAT3151
C2-
VOUT
COUT
1µF
D1
D2
D3
D4
EN/SET
D1
D2
D3
D4
EN/SET
GND
3151.2005.12.1.7
1
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Pin Descriptions
Pin #
Symbol
D4
Function
1
2
3
4
5
Current sink input #4.
EN/SET
C1+
AS2Cwire serial interface control pin.
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
Flying capacitor 1 negative terminal.
C1-
VOUT
Charge pump output to drive load circuit. Requires 1µF capacitor connected
between this pin and ground.
6
7
8
C2+
C2-
VIN
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-.
Flying capacitor 2 negative terminal.
Input power supply. Requires 1µF capacitor connected between this pin and
ground.
9
GND
D1
Ground.
10
11
12
EP
Current sink input #1.
D2
Current sink input #2.
D3
Current sink input #3.
Exposed paddle (bottom). Connect to GND directly beneath package.
Pin Configuration
TDFN33-12
(Top View)
1
2
3
4
5
6
12
11
10
9
D4
EN/SET
C1+
C1-
VOUT
C2+
D3
D2
D1
GND
VIN
C2-
8
7
2
3151.2005.12.1.7
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VIN
Input Voltage
-0.3 to 6
-0.3 to VIN + 0.3
150
V
V
VEN/SET
EN/SET to GND Voltage
2
IOUT
Maximum DC Output Current
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
mA
°C
°C
TJ
-40 to 150
300
TLEAD
Thermal Information3
Symbol
Description
Value
Units
PD
Maximum Power Dissipation4
2.0
50
W
θJA
Maximum Thermal Resistance
°C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-
tions 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 20mW/°C above 25°C.
3151.2005.12.1.7
3
AAT3151
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 TA = 25°C, VIN = 3.5V.
Symbol
Description
Conditions
Min Typ Max Units
Input Power Supply
VIN Operation Range
2.7
5.5
1
V
1X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
0.3
1
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
3
mA
ICC
Operating Current
2X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
2.0
50
3.7
50µA Setting, 1X Mode
EN/SET = 0
µA
µA
mA
%
ISHDN
IDX
Shutdown Current
1
ISINK Current Accuracy2
Current Matching Between Any
Two Current Sink Inputs3, 4
ISET = 30mA, TA = 25°C
VF:D1:D4 = 3.6V
27
30
33
I(D-Match)
0.5
VTH
1X to 1.5X or 1.5X to 2X Transition ISET = 20mA
Threshold at Any ISINK Pin
150
mV
Charge Pump Section
TSS
FCLK
Soft-Start Time
100
µs
Clock Frequency
1000
kHz
EN/SET
VIL
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
VIN = 2.7V
VIN = 5.5V
0.4
75
V
V
VIH
1.4
0.3
TEN/SET LO
µs
ns
µs
µs
µs
µA
TEN/SET HI MIN Minimum EN/SET High Time
50
_
_
TEN/SET HI MAX Maximum EN/SET High Time
75
500
500
1
_
_
TOFF
EN/SET Off Timeout5
EN/SET Latch Timeout6
EN/SET Input Leakage
TLAT
IEN/SET
-1
1. The AAT3151 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.
5. The EN/SET pin must remain logic low (less than VIL) for the duration of longer than 500µs to guarantee the off timeout.
6. The EN/SET pin must remain logic high (greater than VIH) for the duration of longer than 500µs to guarantee the latch timeout.
4
3151.2005.12.1.7
AAT3151
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
90
80
70
60
50
40
30
20
10
0
4.1mA
VF = 2.9V
EN
(2V/div)
CP
(2V/div)
10.2mA
VF = 3.1V
1mA
VF = 2.7V
20mA
VF = 3.4V
VSINK
(500mV/div)
IIN
(200mA/div)
2.6
2.8
2.9
3.1
3.2
3.4
3.6
3.7
3.9
4.0
4.2
Supply Voltage (V)
Time (100µs/div)
Turn-On to 1.5X Mode
(VIN = 3.5V; 20mA Load)
Turn-On to 2X Mode
(VIN = 2.8V; 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-Off from 1.5X Mode
(VIN = 3.5V; 20mA Load)
Current Matching vs. Temperature
20.4
EN
(2V/div)
Channel 2
20.2
20.0
Channel 4
VF
(1V/div)
19.8
Channel 3
Channel 1
19.6
19.4
19.2
19.0
IIN
(100mA/div)
-40
-20
0
20
40
60
80
Temperature (°C)
Time (500µs/div)
3151.2005.12.1.7
5
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
Load Characteristics
(VIN = 3.7V; 1.5X Mode; 15mA Load)
Load Characteristics
(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
(VIN = 3.9V; 1.5X Mode; 20mA Load)
Load Characteristics
(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)
Load Characteristics
(VIN = 4.2V; 1.5X Mode; 30mA Load)
Load Characteristics
(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)
Time (500ns/div)
6
3151.2005.12.1.7
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Typical Characteristics
EN/SET Latch Timeout vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
400
350
350
300
300
250
200
150
100
50
-40°C
-40°C
250
200
150
25°C
85°C
25°C
85°C
100
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
Input Voltage (V)
Input Voltage (V)
Input Ripple vs. Input Voltage
Enable Threshold High vs. Input Voltage
1.2
1.1
1
18
16
14
12
10
8
-40°C
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
20mA
30mA
25°C
85°C
6
4
10.2mA
2
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
2.50 2.67 2.84 3.01 3.18 3.35 3.52 3.69 3.86 4.03 4.20
Input Voltage (V)
Input Voltage (V)
Enable Threshold Low vs. Input Voltage
1.2
1.1
1
-40°C
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
25°C
85°C
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)
3151.2005.12.1.7
7
AAT3151
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
D/A
D/A
D/A
D1
D2
D3
6 x 16 bit
ROM
AS2Cwire
Interface
EN/SET
6 x 16 bit
ROM
D/A
D4
GND
per channel. The AS2Cwire serial interface enables
the AAT3151 and sets the constant current sink
magnitudes. AS2Cwire addressing allows the LED
main channels D1-D3 to be controlled independ-
ently from the LED sub-channel D4.
Functional Description
The AAT3151 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 AAT3151
charge pump is enabled when any of the four cur-
rent 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.
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 to change linearly when the settings in the
scale 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.
The AAT3151 requires only four external compo-
nents: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
ceramic input capacitor (CIN), and one 1µF ceram-
ic charge pump output capacitor (COUT).
Since the constant current levels for the AAT3151
are programmable, no PWM (pulse width modula-
tion) or additional control circuitry are 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 seri-
The AAT3151 constant current sinks can drive four
individual LEDs with a maximum current of 30mA
8
3151.2005.12.1.7
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
AS2Cwire Serial Interface
al 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 program-
mability and real-time control of LED brightness.
The 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 AAT3151 main and sub-chan-
nels can be programmed together or independent-
ly from one another.
For each Max Current scale, 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
(see Table 1).
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 ris-
ing 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 multi-
ple writes to the corresponding data register are
allowed.
The AAT3151 has an additional Low Current mode
with reduced quiescent current. This mode is espe-
cially 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 back-
lighting state.
20mA Max1 30mA Max 15mA Max
Data
IOUT (mA)
IOUT (mA)
IOUT (mA)
1
2
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
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
3
4
5
When EN/SET is held low for an amount of time
greater than TOFF, the AAT3151 enters shutdown
mode and draws less than 1µA from the supply.
Address 1 is the default address on the first rising
edge after the AAT3151 has been disabled.
Whenever shutdown mode is entered, all registers
are reset to 1.
6
7
8
9
7.9
10
11
12
13
14
15
16
7.0
6.3
5.7
8.6
5.1
7.6
4.4
6.7
4.1
6.2
0.0
0.0
Table 1: Constant Current Programming
Levels (mA)2.
1. The device defaults to the 20mA Max scale. Use the Max Current Register to change the Max Scale.
2. There is an additional Low Current mode with currents down to 50µA. See the Low Current Register Settings section.
3151.2005.12.1.7
9
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
AS2Cwire Serial Interface Timing
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
Address
1
2
17
18
1
2 . . .
n <= 16
2
1
1
1
n
Data Reg 1
Data Reg 2
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-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. Address 5 programs the Low Current
register. The Low Current register controls the effi-
cient Low Current mode.
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 AAT3151 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 col-
umn. 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 according to the Constant Current
Programming Levels table.
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. 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 Table 2 for the current level set-
tings and main/sub-configurations that result.
The AAT3151 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 use-
ful for applications requiring an "always on" condi-
tion, such as transmissive displays. As an exam-
ple, 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.
EN/SET
Edges
Addressed
Register
Address
1
17
1&2: D1-D4
Current
2
3
4
5
18
19
20
21
1: D1-D3 Current
2: D4 Current
3: Max Current
4: Low Current
Table 2: Low Current Register Settings.
10
3151.2005.12.1.7
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
The AAT3151 is also equipped with an "auto-disable"
feature to protect against an LED failure condition.
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode1
Thermal Protection
The AAT3151 has a thermal protection circuit that
will shut down the charge pump if the die tempera-
ture rises above the thermal limit, as is the case
during a short-circuit of the VOUT pin.
Table 3: Max Current Register Settings—
Address 4.
Data
D1-D3 (mA)
D4 (mA)
1
2
0
0
0
0
Applications Information
LED Selection
3
0
0
4
0
0
The AAT3151 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3151 to drive most types of LEDs with for-
ward voltage specifications ranging from 2.0V to
4.3V. LED applications may include main and sub-
LCD display backlighting, camera photo-flash appli-
cations, color (RGB) LEDs, infrared (IR) diodes for
remotes, and other loads benefiting from a regulat-
ed output current generated from a varying input
voltage. Since the D1 to D4 constant current sinks
are matched with negligible voltage dependence,
the LED brightness will be matched regardless of
the specific LED forward voltage (VF) levels.
5
0
0.05
0.5
1
6
0
7
0
8
0
2
9
0.05
0.5
1
0
10
11
12
13
14
15
16
0
0
2
0
0.05
0.5
1
0.05
0.5
1
2
2
In some instances (e.g., in high luminous output
applications such as photo flash), it may be neces-
sary to drive high-VF type LEDs. The low dropout
current sinks in the AAT3151 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.
Table 4: Low Current Register Settings—
Address 5.
Disabled Current Sinks
Current sinks can be paralleled to drive high-cur-
rent LEDs without complication.
Current sink inputs that are not used should be dis-
abled. 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.
Device Switching Noise Performance
The AAT3151 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communica-
tion 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
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 chan-
nel is 120µA.
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.
3151.2005.12.1.7
11
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
DC/DC boost converter white LED backlight solu-
Load Switch Mode Efficiency
tions. The AAT3151 soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
The AAT3151 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:
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the follow-
ing sections only accounts for the efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3151, it is very dif-
ficult to measure efficiency in terms of a percent
value comparing input power over output power.
POUT
PIN
η =
The expression to define the ideal efficiency (η)
can be rewritten as:
Since the AAT3151 inputs are pure constant current
sinks and typically drive individual loads, it is difficult
to measure the output voltage for a given input (D1
to D4) to derive an overall output power measure-
ment. For any given application, white LED forward
voltage levels can differ, yet the load drive current
will be maintained as a constant.
POUT VOUT × IOUT VOUT
η =
=
=
PIN
VIN × IOUT
VIN
-or-
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 applica-
tion should be based on trade-offs of size, external
component count, reliability, operating range, and
total energy usage...not just % efficiency.
V
⎛
⎝
⎞
⎠
OUT
η(%) = 100
VIN
Charge Pump Section Efficiency
The AAT3151 contains a fractional charge pump
that will boost the input supply voltage when VIN is
less than the voltage required on the constant cur-
rent sink inputs. The efficiency (η) can be simply
defined as a linear voltage regulator with an effec-
tive output voltage that is equal to one and one 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.
The AAT3151 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 inputs D1 through D4 for a
given constant current setting. Depending on the
combination of VIN and voltages sensed at the cur-
rent 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.
POUT
PIN
η =
In addition, with an ideal 1.5X charge pump, the
output current may be expressed as 2/3 of the
12
3151.2005.12.1.7
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
input current. The expression to define the ideal
efficiency (η) can be rewritten as:
print, and is non-polarized. Low ESR ceramic
capacitors help maximize charge pump transient
response. Since ceramic capacitors are non-polar-
ized, they are not prone to incorrect connection
damage.
POUT
PIN
VOUT × IOUT
=
VOUT
η =
=
VIN × 1.5IOUT 1.5VIN
-or-
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 typi-
cally measured in milliohms for ceramic capacitors
and can range to more than several ohms for tanta-
lum or aluminum electrolytic capacitors.
VOUT
⎛
⎝
⎞
⎠
η(%) = 100
1.5V
IN
Capacitor Selection
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 per-
formance. 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 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.
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 val-
ues are usually composed of X7R, X5R, Z5U, or
Y5V dielectric materials. Large ceramic capacitors
(i.e., greater than 2.2µF) are often available in low-
cost Y5V and Z5U dielectrics, but capacitors
greater than 1µF are not typically required for
AAT3151 applications.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3151. Ceramic capacitors offer many
advantages over their tantalum and aluminum elec-
trolytic counterparts. A ceramic capacitor has very
low ESR, is lowest cost, has a smaller PCB foot-
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.
3151.2005.12.1.7
13
AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
AAT3151IWP-T1
TDFN33-12
NLXYY
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
TDFN33-12
Index Area
(D/2 x E/2)
Detail "B"
0.3 0.10 0.16 0.375 0.125
0.075 0.075
0.1 REF
3.00 0.05
1.70 0.05
Detail "A"
Top View
Bottom View
Pin 1 Indicator
(optional)
7.5° 7.5°
Detail "B"
Option A:
Option B:
C0.30 (4x) max
Chamfered corner
R0.30 (4x) max
Round corner
0.05 0.05
Detail "A"
Side View
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
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
14
3151.2005.12.1.7
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