AAT3151B_08 [ANALOGICTECH]
High Efficiency 1X/1.5X Charge Pump For White LED Applications; 高效率1X / 1.5X电荷泵为白光LED应用
| 型号： | AAT3151B_08 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High Efficiency 1X/1.5X Charge Pump For White LED Applications |
| 文件： | 总13页 (文件大小：291K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
General Description
Features
The AAT3151B is a low noise, constant frequency charge
pump DC/DC converter that uses a dual mode load
switch (1X) and fractional (1.5X) charge pump conver-
sion to maximize efficiency for white LED applications.
The AAT3151B 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 operated individually or in parallel for driv-
ing higher-current LEDs. A low external parts count (two
1μF flying capacitors and two small 1μF capacitors at VIN
and VOUT) makes the AAT3151B 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
▪
▪
▪
▪
• Dual Mode 1X and 1.5X Charge Pump for Maximum
Efficiency and VF Coverage
• Drives Four Channels of LEDs
• 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
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.
• IQ <1μA in Shutdown
• TDFN33-12 Package
The charge pump output of the AAT3151B 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 current during start-up. A low-current
shutdown feature 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 AAT3151B 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
C1-
1μF
C2+
C2
1μF
AAT3151B
C2-
VOUT
COUT
1μF
D1
D2
D3
D4
EN/SET
D1
D2
D3
D4
EN/SET
GND
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3151B.2008.02.1.1
1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Pin Descriptions
Pin #
Symbol
Function
1
2
3
4
D4
EN/SET
C1+
Current sink input #4.
AS2Cwire serial interface control pin.
Flying capacitor 1 positive terminal. Connect a 1μF ceramic capacitor between C1+ and C1-.
Flying capacitor 1 negative terminal.
C1-
Charge pump output to drive load circuit. Requires a 1μF or larger ceramic capacitor connected between
this pin and ground.
5
VOUT
6
7
8
C2+
C2-
VIN
GND
D1
Flying capacitor 2 positive terminal. Connect a 1μF ceramic capacitor between C2+ and C2-.
Flying capacitor 2 negative terminal.
Input power supply. Requires a 1μF or larger ceramic capacitor connected between this pin and ground.
Ground.
Current sink input #1.
Current sink input #2.
Current sink input #3.
Exposed paddle (bottom). Connect to GND directly beneath package.
9
10
11
12
EP
D2
D3
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
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3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VIN
Input Voltage
EN/SET to GND Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
-0.3 to 6
-0.3 to VIN + 0.3
150
V
V
mA
°C
°C
VEN/SET
2
IOUT
TJ
TLEAD
-40 to 150
300
Thermal Information3
Symbol
Description
Maximum Power Dissipation4
Maximum Thermal Resistance
Value
Units
PD
θJA
2.0
50
W
°C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 20mW/°C above 25°C.
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3151B.2008.02.1.1
3
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X 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
Input Power Supply
Conditions
Min Typ Max Units
VIN
Operation Range
2.7
27
5.5
1
3
V
1X Mode, 3.0 ≥ VIN ≥ 5.5, Active, No Load Current
1.5X Mode, 3.0 ≥ VIN ≥ 5.5, Active, No Load Current
50μA Setting, 1X Mode
EN/SET = 0
ISET = 30mA, TA = 25°C
0.3
1
50
mA
ICC
Operating Current
μA
μA
mA
ISHDN
IDX
Shutdown Current
ISINK Current Accuracy2
1
33
30
Current Matching Between Any
Two Current Sink Inputs3, 4
1X to 1.5X Transition Threshold
at Any ISINK Pin
I(D-Match)
VTH
VF:D1:D4 = 3.6V
ISET = 20mA
0.5
%
150
mV
Charge Pump Section
TSS
FCLK
Soft-Start Time
Clock Frequency
100
1000
μs
kHz
EN/SET
VIL
VIH
TEN/SET LO
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
VIN = 2.7V
VIN = 5.5V
0.4
75
V
V
1.4
0.3
μs
ns
μs
μs
μs
μA
TEN/SET_HI_MIN Minimum EN/SET High Time
TEN/SET_HI_MAX Maximum EN/SET High Time
50
75
500
500
1
TOFF
TLAT
IEN/SET
EN/SET Off Timeout5
EN/SET Latch Timeout6
EN/SET Input Leakage
-1
1. The AAT3151B is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and cor-
relation 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.
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3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Typical Characteristics
3151B Backlight Efficiency vs. Supply Voltage
Turn-On to 1X Mode
(VIN = 4.2V; 20mA Load)
100
90
20mA
EN
(2V/div)
80
70
60
50
CP
(2V/div)
VSINK
(500mV/div)
1mA
10.2mA
40
IIN
(200mA/div)
30
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
Supply Voltage (V)
Time (100µs/div)
Turn-On to 1.5X Mode
(VIN = 3.5V; 20mA Load)
Turn-Off from 1.5X Mode
(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
20.4
Channel 2
20.2
20.0
Channel 4
19.8
Channel 3
Channel 1
19.6
19.4
19.2
19.0
-40
-20
0
20
40
60
80
Temperature (°C)
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3151B.2008.02.1.1
5
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Typical Characteristics
Load Characteristics
(VIN = 3.7V; 1.5X Mode; 15mA Load)
Load Characteristics
(VIN = 3.9V; 1.5X 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)
EN/SET Latch Timeout vs. Input Voltage
350
300
250
200
150
100
50
VIN
(40mV/div)
-40°C
CP
(40mV/div)
25°C
85°C
VSINK
(40mV/div)
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
Time (500ns/div)
Input Voltage (V)
Input Ripple vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
20
18
16
14
12
10
8
400
350
30mA
300
-40°C
20mA
250
200
150
6
25°C
85°C
10.2mA
4
100
50
0
2
0
2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00
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)
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3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Typical Characteristics
Enable Threshold High vs. Input Voltage
Enable Threshold Low vs. Input Voltage
1.2
1.1
1.2
1.1
1
1
-40°C
0.9
0.8
0.7
0.6
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-40°C
25°C
85°C
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
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)
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3151B.2008.02.1.1
7
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Functional Block Diagram
C1+ C1- C2+ C2-
1X and 1.5X
Charge Pump
VIN
VOUT
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
D/A
D1
D2
D3
D4
D/A
D/A
D/A
6 x 16 bit
ROM
AS2Cwire
Interface
EN/SET
GND
Because the inputs D1 to D4 are true independent con-
stant 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.
Functional Description
The AAT3151B is a dual mode load switch (1X) and high
efficiency (1.5X) charge pump device intended for white
LED backlight applications. To maximize power conver-
sion 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 volt-
age. As the battery discharges over time, the AAT3151B
charge pump is enabled when any of the four current
sinks near dropout.
Since the constant current levels for the AAT3151B are
programmable, no PWM (pulse width modulation) 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 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 pro-
grammability and real-time control of LED brightness.
The AAT3151B requires only four external components:
two 1μF ceramic capacitors for the charge pump flying
capacitors (C1 and C2), one 1μF ceramic input capacitor
(CIN), and one 1μF ceramic charge pump output capaci-
tor (COUT).
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).
The AAT3151B constant current sinks can drive four indi-
vidual LEDs with a maximum current of 30mA per chan-
nel. The AS2Cwire serial interface enables the AAT3151B
and sets the constant current sink magnitudes.
The AAT3151B has an additional Low Current mode with
reduced quiescent current. 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 maintain-
ing a continuous backlighting state.
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.
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3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
held high for time TLAT. Address or data is differentiated
by the number of EN/SET rising edges. Since the data
20mA Max1
IOUT (mA)
30mA Max 15mA Max
Data
IOUT (mA)
IOUT (mA)
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, fol-
lowed 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.
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
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
8.6
7.6
6.7
6.2
When EN/SET is held low for an amount of time greater
than TOFF, the AAT3151B enters shutdown mode and
draws less than 1μA from the supply. Address 1 is the
default address on the first rising edge after the
AAT3151B has been disabled. Whenever shutdown mode
is entered, all registers are reset to 1.
5.1
4.4
4.1
0.0
0.0
Table 1: Constant Current Programming
Levels (mA)2.
AS2Cwire Addressing
AS2Cwire Serial Interface
A number of addresses are available to control all of the
part’s functionality. Use Address 1 to program all four
LED channels to any one of 16 possible settings that
depend on the Max Current scale setting. 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 highly
efficient Low Current mode.
The AS2Cwire single wire interface is used to set the pos-
sible combinations of current levels and LED channel
states.
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
AS2Cwire Serial Interface Timing
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
1
2
17
1
18
1
2 . . .
n <= 16
2
Address
1
n
Data Reg 1
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.
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3151B.2008.02.1.1
9
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
When the Max Current register is programmed to 1, 4,
or 5, changing the data for Address 1 will result in the
corresponding values found in the Constant Current
Programming Levels table. When the Max Current regis-
ter is programmed to 4, the part is programmed to oper-
ate in Low Current mode and the Data for Address 1 is
irrelevant. In Low Current mode, the Low Current regis-
ter takes precedence. See Table 4 for the available cur-
rent level settings.
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 qui-
escent current.
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
Address EN/SET Edges
Addressed Register
1
4
5
17
20
21
D1-D4 Current
Max Current
Low Current
Table 3: Max Current Register Settings—
Address 4.
Table 2: Addresses for Setting Current Level.
Data
D1-D4 (mA)
1
2
3
4
0.05
0.5
1
Max Current and Low Current Registers
Use the Max Current and Low Current registers to pro-
gram constant current settings outside of the 20mA Max
scale. By default (without changing the Max Current reg-
ister), the AAT3151B 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
2
Table 4: Low Current Register Settings—
Address 5.
Disabled Current Sinks
Current sink inputs that are not used should be disabled.
To disable and properly terminate unused current sink
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 according to the
Constant Current Programming Levels table.
inputs, they must be tied to VOUT
.
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from pre-
maturely activating. When properly terminated, only a
small sense current flows for each disabled channel. The
sense current for each disabled channel is 120μA.
The AAT3151B has a distinct Low Current mode with
ultra-low quiescent current. For drive currents of 2mA or
less, the part operates with significantly reduced quies-
cent 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 reg-
ister with 4 rising edges and pause for TLAT. Address the
The AAT3151B is also equipped with an “auto-disable”
feature to protect against an LED failure condition.
Thermal Protection
The AAT3151B has a 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.
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3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
given application, white LED forward voltage levels can
differ, yet the load drive current will be maintained as a
constant.
Applications Information
LED Selection
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 AAT3151B is specifically intended for driving white
LEDs. However, the device design will allow the AAT3151B
to drive most types of LEDs with forward voltage speci-
fications ranging from 2.0V to 4.3V. LED applications
may include main and sub-LCD display backlighting,
camera photo-flash applications, color (RGB) LEDs,
infrared (IR) diodes for remotes, and other loads bene-
fiting from a regulated output current generated from a
varying input voltage. Since the D1 to D4 constant cur-
rent sinks are matched with negligible voltage depen-
dence, the LED brightness will be matched regardless of
the specific LED forward voltage (VF) levels.
The AAT3151B efficiency may be quantified under very
specific conditions and is dependent upon the input volt-
age 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 current sinks, the device will
operate in load switch mode. When any one of the volt-
ages sensed at the current sinks nears dropout, the
device will operate in 1.5X charge pump mode. Each of
these modes will yield different efficiency values. Refer
to the following two sections for explanations for each
operational mode.
In some instances (e.g., in high luminous output appli-
cations such as photo flash), it may be necessary to
drive high-VF type LEDs. The low dropout current sinks
in the AAT3151B 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 paral-
leled to drive high-current LEDs without complication.
Device Switching Noise Performance
The AAT3151B operates at a fixed frequency of approxi-
mately 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 induc-
tor-based DC/DC boost converter white LED backlight
solutions. The AAT3151B soft-start feature prevents
noise transient effects associated with inrush currents
during start-up of the charge pump circuit.
Load Switch Mode Efficiency
The AAT3151B load switch mode is operational at all
times and functions alone to enhance device power con-
version 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
η =
Power Efficiency and Device Evaluation
The expression to define the ideal efficiency (η) can be
rewritten as:
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 architec-
ture and design of the AAT3151B, it is very difficult to
measure efficiency in terms of a percent value compar-
ing input power over output power.
POUT VOUT · IOUT VOUT
η =
=
=
PIN
VIN · IOUT
VIN
-or-
Since the AAT3151B 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 measurement. For any
V
⎛
⎝
⎞
⎠
OUT
η(%) = 100
VIN
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3151B.2008.02.1.1
11
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Charge Pump Section Efficiency
Capacitor Characteristics
The AAT3151B contains a fractional charge pump that
will boost the input supply voltage when VIN is less than
the voltage required on the constant current sink inputs.
The efficiency (η) can be simply defined as a linear volt-
age regulator with an effective 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 typi-
cally be expressed as the output power divided by the
input power.
Ceramic composition capacitors are highly recommended
over all other types of capacitors for use with the
AAT3151B. Ceramic capacitors offer many advantages
over their tantalum and aluminum electrolytic counter-
parts. A ceramic capacitor 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.
POUT
PIN
η =
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 connec-
tions, size or area, material composition, and ambient
temperature. Capacitor ESR is typically measured in mil-
liohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
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:
POUT
PIN
VOUT · IOUT
VOUT
η =
=
=
VIN · 1.5IOUT
1.5VIN
Ceramic Capacitor Materials
-or-
Ceramic capacitors less than 0.1μF are typically made
from NPO or C0G materials. NPO and C0G materials gen-
erally have tight tolerance and are very stable over tem-
perature. 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 low-cost Y5V and Z5U dielectrics, but capac-
itors greater than 1μF are not typically required for
AAT3151B applications.
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 performance. Optimum
performance will be obtained when low equivalent series
resistance (ESR) ceramic capacitors are used. In gener-
al, 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.
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.
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12
3151B.2008.02.1.1
PRODUCT DATASHEET
AAT3151B
TM
ChargePump
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
AAT3151BIWP-T1
TDFN33-12
ZOXYY
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/about/quality.aspx.
Package Information3
TDFN33-12
Index Area
Detail "A"
0.43 0.05
0.1 REF
C0.3
Pin 1 Indicator
(optional)
3.00 0.05
1.70 0.05
Top View
Bottom View
Detail "A"
0.05 0.05
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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.
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3151B.2008.02.1.1
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