202144A.pdf

DATA SHEET
AAT3151B
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 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 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) 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
• IQ <1µA in Shutdown
• TDFN33-12 Package
Skyworks' 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 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
CIN
1µF
C1C2+
C2
1µF
AAT3151B
C2VOUT
D1
EN/SET
D2
D3
D4
COUT
1µF
D1
EN/SET
D2
D3
GND
D4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
1
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Pin Descriptions
Pin #
Symbol
1
2
3
4
D4
EN/SET
C1+
C1-
5
VOUT
6
7
8
9
10
11
12
EP
C2+
C2VIN
GND
D1
D2
D3
Function
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.
Charge pump output to drive load circuit. Requires a 1µF or larger ceramic capacitor connected between
this pin and ground.
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.
Pin Configuration
TDFN33-12
(Top View)
D4
EN/SET
C1+
C1VOUT
C2+
2
1
12
2
11
3
10
4
9
5
8
6
7
D3
D2
D1
GND
VIN
C2-
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Absolute Maximum Ratings1
Symbol
VIN
Description
Input Voltage
EN/SET to GND Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
VEN/SET
IOUT2
TJ
TLEAD
Value
Units
-0.3 to 6
-0.3 to VIN + 0.3
150
-40 to 150
300
V
V
mA
°C
°C
Value
Units
2.0
50
W
°C/W
Thermal Information3
Symbol
PD
qJA
Description
Maximum Power Dissipation4
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 20mW/°C above 25°C.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
3
DATA SHEET
AAT3151B
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
Conditions
Input Power Supply
VIN
Operation Range
ICC
ISHDN
IDX
Operating Current
Shutdown Current
ISINK Current Accuracy2
Current Matching Between Any
I(D-Match)
Two Current Sink Inputs3, 4
1X to 1.5X Transition Threshold
VTH
at Any ISINK Pin
Charge Pump Section
TSS
Soft-Start Time
FCLK
Clock Frequency
EN/SET
VIL
Enable Threshold Low
VIH
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 Timeout5
TLAT
EN/SET Latch Timeout6
IEN/SET
EN/SET Input Leakage
Min
Typ
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
50µA Setting, 1X Mode
EN/SET = 0
ISET = 30mA, TA = 25°C
0.3
1
50
27
Max
Units
5.5
1
3
V
1
33
30
mA
µA
µA
mA
VF:D1:D4 = 3.6V
0.5
%
ISET = 20mA
150
mV
100
1000
µs
kHz
VIN = 2.7V
VIN = 5.5V
0.4
1.4
0.3
75
50
-1
75
500
500
1
V
V
µs
ns
µs
µs
µs
µA
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
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
DATA SHEET
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
Efficiency (%)
90
EN
(2V/div)
20mA
80
CP
(2V/div)
70
60
50
1mA
40
30
VSINK
(500mV/div)
IIN
(200mA/div)
10.2mA
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 (100µs/div)
Supply Voltage (V)
Turn-On to 1.5X Mode
Turn-Off from 1.5X Mode
(VIN = 3.5V; 20mA Load)
(VIN = 3.5V; 20mA Load)
EN
(2V/div)
EN
(2V/div)
VF
(1V/div)
CP
(2V/div)
VSINK
(500mV/div)
IIN
(100mA/div)
IIN
(200mA/div)
Time (100µs/div)
Time (500µs/div)
Current Matching vs. Temperature
20.4
Channel 2
Current (mA)
20.2
20.0
Channel 4
19.8
Channel 3
19.6
Channel 1
19.4
19.2
19.0
-40
-20
0
20
40
60
80
Temperature (ºC)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
5
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Typical Characteristics
Load Characteristics
Load Characteristics
(VIN = 3.7V; 1.5X Mode; 15mA Load)
(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
EN/SET Latch Timeout (ms)
(VIN = 4.2V; 1.5X Mode; 30mA Load)
VIN
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
350
300
-40°C
250
200
150
25°C
100
85°C
50
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Time (500ns/div)
Input Voltage (V)
Input Ripple vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
20
30mA
18
350
16
300
Amplitude (mV)
EN/SET Off Timeout (µs)
400
-40°C
250
200
150
25°C
85°C
100
14
20mA
12
10
8
6
10.2mA
4
2
50
0
2.50
0
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
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)
6
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
4.75
5.00
DATA SHEET
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
-40°C
0.9
0.8
0.7
0.6
25°C
85°C
0.5
0.4
0.3
0.2
Enable Threshold Low (V)
Enable Threshold High (V)
1.2
1.1
1
0.9
-40°C
0.8
0.7
0.6
0.5
25°C
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
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)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
7
DATA SHEET
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
6 x 16 bit
ROM
EN/SET
AS 2 Cwire
Interface
D/A
D1
D/A
D2
D/A
D3
D/A
D4
GND
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 current
sinks near dropout.
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 capacitor (COUT).
The AAT3151B constant current sinks can drive four individual LEDs with a maximum current of 30mA per channel. The AS2Cwire serial interface enables the AAT3151B
and sets the constant current sink magnitudes.
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.
8
Because the inputs D1 to D4 are true independent constant current sinks, the voltage observed on any single
given input will be determined by the difference between
VOUT and the actual forward voltage (VF) of the LED being
driven.
Since the constant current levels 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 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. 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 has an additional Low Current mode with
reduced quiescent current. This mode is especially useful
for low-current applications where a continuous, lowcurrent state is maintained. The reduction in quiescent
current significantly reduces the impact due to maintaining a continuous backlighting state.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Data
20mA Max1
IOUT (mA)
30mA Max
IOUT (mA)
15mA
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
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
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 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.
Table 1: Constant Current Programming
Levels (mA)2.
AS2Cwire Addressing
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.
AS2Cwire Serial Interface
The AS2Cwire single wire interface is used to set the possible 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
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
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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
9
DATA SHEET
AAT3151B
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 register is programmed to 4, the part is programmed 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.
Address
EN/SET Edges
Addressed Register
1
4
5
17
20
21
D1-D4 Current
Max Current
Low Current
Table 2: Addresses for Setting Current Level.
Max Current and Low Current Registers
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 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.
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 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
10
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.
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
Table 3: Max Current Register Settings—
Address 4.
Data
D1-D4 (mA)
1
2
3
4
0.05
0.5
1
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
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 channel is 120µA.
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 shortcircuit of the VOUT pin.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Applications Information
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 forward voltage specifications 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 benefiting from a regulated 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.
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 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-current LEDs without complication.
Device Switching Noise Performance
The AAT3151B operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that
can interfere with the RF operation of cellular telephone
handsets or other communication devices. Back-injected
noise appearing on the input pin of the charge pump is
20mV peak-to-peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight
solutions. The AAT3151B soft-start feature prevents
noise transient effects associated with inrush currents
during start-up of the charge pump circuit.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following
sections only accounts for the efficiency of the charge
pump section itself. Due to the unique circuit architecture and design of the AAT3151B, it is very difficult to
measure efficiency in terms of a percent value comparing input power over output power.
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
given application, white LED forward voltage levels can
differ, yet the load 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 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 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 charge pump mode. Each of
these modes will yield different efficiency values. Refer
to the following two sections for explanations for each
operational mode.
Load Switch Mode Efficiency
The 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:
η=
POUT
PIN
The expression to define the ideal efficiency (h) can be
rewritten as:
η=
POUT VOUT · IOUT VOUT
=
=
PIN
VIN · IOUT
VIN
-or-
η(%) = 100
 VOUT 
 VIN 
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DATA SHEET
AAT3151B
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 (h) can be simply defined as a linear voltage regulator with an effective output voltage that is
equal to one and one half or two times the input voltage.
Efficiency (h) for an ideal 1.5X charge pump can typically 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 counterparts. 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 nonpolarized, they are not prone to incorrect connection
damage.
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 (h) can be
rewritten as:
η=
POUT
VOUT · IOUT
VOUT
=
=
PIN
VIN · 1.5IOUT
1.5VIN
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal to a
capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient
temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
Ceramic Capacitor Materials
-or-
η(%) = 100
 VOUT 
 1.5VIN
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 general, low ESR may be defined as less than 100mW. 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.
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Equivalent Series Resistance
Ceramic capacitors less than 0.1µF are typically made
from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed
of X7R, X5R, Z5U, or Y5V dielectric materials. Large
ceramic capacitors (i.e., greater than 2.2µF) are often
available in low-cost Y5V and Z5U dielectrics, but capacitors greater than 1µF are not typically required for
AAT3151B 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
DATA SHEET
AAT3151B
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-12
ZOXYY
AAT3151BIWP-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information3
TDFN33-12
Index Area
0.43 ± 0.05
Detail "A"
0.45 ± 0.05
2.40 ± 0.05
3.00 ± 0.05
0.1 REF
C0.3
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
0.23 ± 0.05
Pin 1 Indicator
(optional)
0.05 ± 0.05
All dimensions in millimeters.
0.23 ± 0.05
0.75 ± 0.05
Detail "A"
Side View
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.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202144A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 6, 2012
13