AAT3151B [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 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High Efficiency 1X/1.5X Charge Pump For White LED Applications |
| 文件： | 总15页 (文件大小：266K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
™
ChargePump
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 conversion 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 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 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
2
AnalogicTech's AS Cwire™ (Advanced Simple
Built-In Auto-Disable for Short-Circuit
Automatic Soft Start
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 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 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
1μF
C1-
C2+
C2
1μF
AAT3151B
C2-
VOUT
COUT
1μF
D1
D2
D3
D4
EN/SET
D1
D2
D3
D4
EN/SET
GND
3151B.2007.09.1.0
1
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
Pin Descriptions
Pin #
Symbol
Function
1
2
3
4
5
D4
EN/SET
C1+
C1-
VOUT
Current sink input #4.
AS Cwire serial interface control pin.
Flying capacitor 1 positive terminal. Connect a 1µF ceramic capacitor between C1+ and C1-.
Flying capacitor 1 negative terminal.
Charge pump output to drive load circuit. Requires a 1µF or larger ceramic capacitor con-
nected between this pin and ground.
2
6
7
8
C2+
C2-
VIN
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.
9
GND
D1
D2
Ground.
Current sink input #1.
Current sink input #2.
Current sink input #3.
10
11
12
EP
D3
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
3151B.2007.09.1.0
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
1
Absolute Maximum Ratings
Symbol
Description
Value
Units
VIN
VEN/SET
IOUT
TJ
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
2
-40 to 150
300
TLEAD
3
Thermal Information
Symbol
Description
Maximum Power Dissipation
Maximum Thermal Resistance
Value
2.0
50
Units
W
°C/W
4
PD
θJA
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.
3151B.2007.09.1.0
3
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
1
Electrical Characteristics
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
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
0.3
1
ICC
Operating Current
3
mA
50µA Setting, 1X Mode
EN/SET = 0
ISET = 30mA, TA = 25°C
50
µA
µA
mA
ISHDN
IDX
Shutdown Current
ISINK Current Accuracy
1
33
2
27
30
Current Matching Between Any
Two Current Sink Inputs
1X to 1.5X Transition Threshold at
Any ISINK Pin
I(D-Match)
VTH
VF:D1:D4 = 3.6V
ISET = 20mA
0.5
%
3, 4
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
50
_
_
TEN/SET HI MAX Maximum EN/SET High Time
75
500
500
1
_
_
5
TOFF
TLAT
IEN/SET
EN/SET Off Timeout
EN/SET Latch Timeout
EN/SET Input Leakage
6
-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 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
3151B.2007.09.1.0
AAT3151B
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)
3151B.2007.09.1.0
5
AAT3151B
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)
EN/SET Latch Timeout vs. Input Voltage
Load Characteristics
(VIN = 4.2V; 1.5X Mode; 30mA Load)
350
300
VIN
(40mV/div)
250
-40°C
200
150
CP
(40mV/div)
25°C
85°C
100
50
0
VSINK
(40mV/div)
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)
Time (500ns/div)
EN/SET Off Timeout vs. Input Voltage
Input Ripple vs. Input Voltage
400
350
300
250
200
150
100
50
20
18
16
14
12
10
8
30mA
-40°C
20mA
25°C
85°C
6
10.2mA
4
2
0
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)
6
3151B.2007.09.1.0
AAT3151B
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
-40°C
0.9
0.8
0.7
0.6
25°C
85°C
0.5
0.4
0.3
0.2
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)
3151B.2007.09.1.0
7
AAT3151B
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
D/A
D2
6 x 16 bit
ROM
D/A
D3
AS2Cwire
Interface
EN/SET
D/A
D4
GND
enables the AAT3151B and sets the constant cur-
rent sink magnitudes.
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 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 AAT3151B
charge pump is enabled when any of the four cur-
rent sinks near dropout.
Constant Current Output Level Settings
The constant current level for the LED channels is
2
set via the AS Cwire 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 AAT3151B 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 AAT3151B
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-
al interface (>1MHz data rate), the LED current
The AAT3151B constant current sinks can drive
four individual LEDs with a maximum current of
2
30mA per channel. The AS Cwire serial interface
8
3151B.2007.09.1.0
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
2
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.
AS Cwire Serial Interface
2
The AS Cwire single wire interface is used to set
the possible combinations of current levels and
LED channel states.
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).
2
AS Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
2
AS Cwire 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,
4
the differentiating number of pulses is 2 or 16, so
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 maintaining a continuous back-
lighting state.
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.
1
20mA Max 30mA Max 15mA Max
Data
IOUT (mA)
IOUT (mA)
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
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
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.
8.6
7.6
6.7
6.2
5.1
4.4
4.1
0.0
0.0
Table 1: Constant Current Programming
2
Levels (mA) .
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.
3151B.2007.09.1.0
9
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
2
AS Cwire Serial Interface Timing
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
1
2
17
1
18
1
2 . . .
n <= 16
2
Address
Data Reg 1
Data Reg 2
1
1
n
2
AS Cwire Addressing
Max Current and Low Current Registers
A number of addresses are available to control all
of the part's functionality. Use Address 1 to pro-
gram all four LED channels to any one of 16 pos-
sible 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.
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 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 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 cu rrent
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,
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 register is programmed to 4, the part is pro-
grammed to operate in Low Current mode and the
Data for Address 1 is irrelevant. In Low Current
mode, the Low Current register takes precedence.
See Table 4 for the available current level settings.
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 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
4
5
17
20
21
D1-D4 Current
Max Current
Low Current
Table 2: Low Current Register Settings.
10
3151B.2007.09.1.0
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
Applications Information
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
LED Selection
The AAT3151B is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3151B 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.
1
Table 3: Max Current Register Settings—
Address 4.
Data
D1-D4 (mA)
1
2
3
4
0.05
0.5
1
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 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 paralleled to drive high-cur-
rent LEDs without complication.
Table 4: Low Current Register Settings—
Address 5.
Disabled Current Sinks
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
.
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.
Device Switching Noise Performance
The AAT3151B 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
DC/DC boost converter white LED backlight solu-
tions. The AAT3151B soft-start feature prevents
noise transient effects associated with inrush cur-
rents during start-up of the charge pump circuit.
The AAT3151B is also equipped with an "auto-dis-
able" 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 tempera-
ture rises above the thermal limit, as is the case
during a short-circuit of the VOUT pin.
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 AAT3151B, it is very
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
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.
3151B.2007.09.1.0
11
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
Since the AAT3151B inputs are pure constant cur-
rent sinks and typically drive individual loads, it is dif-
ficult to measure the output voltage for a given input
(D1 to D4) to derive an overall output power meas-
urement. For any given application, white LED for-
ward voltage levels can differ, yet the load drive cur-
rent will be maintained as a constant.
The expression to define the ideal efficiency (η)
can be rewritten as:
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 AAT3151B 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 AAT3151B 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 charge pump mode. Each of these modes
will yield different efficiency values. Refer to the fol-
lowing two sections for explanations for each oper-
ational mode.
POUT
PIN
η =
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
The AAT3151B 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
VOUT · IOUT
VOUT
η =
=
=
VIN · 1.5IOUT
1.5VIN
-or-
POUT
PIN
VOUT
η =
⎛
⎝
⎞
⎠
η(%) = 100
1.5V
IN
12
3151B.2007.09.1.0
AAT3151B
High Efficiency 1X/1.5X 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 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.
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.
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
AAT3151B applications.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3151B. Ceramic capacitors offer
many advantages over their tantalum and alu-
minum electrolytic counterparts. A ceramic capac-
itor has very low ESR, is lowest cost, has a small-
er 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 con-
nection damage.
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.
3151B.2007.09.1.0
13
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
Ordering Information
1
2
Package
Marking
Part Number (Tape and Reel)
TDFN33-12
ZOXYY
AAT3151BIWP-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.
3
Package Information
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.
14
3151B.2007.09.1.0
AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED 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 with-
out notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied war-
ranty 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
3151B.2007.09.1.0
15
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