Analogic AAT3122ITP-T1 High efficiency 1x/1.5x fractional charge pump for white led application Datasheet

AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
General Description
Features
The AAT3122 is a low noise, constant frequency
charge pump DC/DC converter that uses a dual
mode load switch (1X) and fractional (1.5X) conversion to increase efficiency in white LED applications. With input voltages ranging from 2.7V to
5.5V, the device can produce an output current of
up to 120mA. A low external parts count (two 1µF
flying capacitors and two small bypass capacitors
at VIN and OUT) makes the AAT3122 ideally suited
for small battery-powered applications.
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•
•
•
•
•
•
•
•
•
•
•
•
•
AnalogicTech's Simple Serial Control™ (S2Cwire™)
interface is used to enable, disable, and set the
LED drive current with a 32-level logarithmic scale
LED brightness control. The AAT3122 has a thermal management system to protect the device in
the event of a short-circuit condition on any of the
output pins. Built-in soft-start circuitry prevents
excessive inrush current during start-up. High
switching frequency enables the use of small external capacitors. A low shutdown current feature disconnects the load from VIN and reduces quiescent
current to less than 1µA. The AAT3122 provides a
single current source output that can be used to
drive up to six LEDs at 20mA each. The AAT3122
is available in a Pb-free TSOPJW-12 package.
ChargePump™
VIN Range: 2.7V to 5.5V
<1µA of Shutdown Current
1 MHz Switching Frequency
Dual Mode 1X and 1.5X Charge Pump for
Maximum Efficiency
Only Four External Components
Simple Serial Control (S2Cwire) Interface
Low Noise Constant Frequency Operation
33% Less Input Current Than Doubler Charge
Pumps
Small Application Circuit
Regulated Output Current
Automatic Soft Start
No Inductors
TSOPJW-12 Package
-40°C to +85°C Temperature Range
Applications
•
•
Programmable Current Source
White LED Backlighting
Typical Application
VIN
C1+
C1
1µF
AAT3122
C1C2+
VOUT
VBATTERY
CIN
1µF
COUT
1µF
C2
1µF
C2-
EN/SET
EN/SET
GND
3122.2005.11.1.3
D
D1
D2
D3
D4
D5
D6
1
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Pin Descriptions
Pin #
Symbol
Function
1
2
3
4
5, 6, 7, 8
9
C2+
OUT
C1C1+
D
EN/SET
10
11
12
IN
GND
C2-
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-.
Charge pump output. Requires 1µF bypass capacitor to ground.
Flying capacitor 1 negative terminal.
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
Output current source with drive capability of up to 120mA.
Input control pin. Serial data interface that controls the level of output current. See
Application Information for more details.
Input power supply. Requires 1µF bypass capacitor to ground.
Ground.
Flying capacitor 2 negative terminal.
Pin Configuration
TSOPJW-12
(Top View)
C2+
OUT
C1C1+
D
D
2
1
12
2
11
3
10
4
9
5
8
6
7
C2GND
IN
EN/SET
D
D
3122.2005.11.1.3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Absolute Maximum Ratings1
Symbol
VIN
VOUT
VEN/SET
VEN/SET(MAX)
IOUT2
TJ
Description
Input Voltage
Charge Pump Output
EN/SET to GND Voltage
Maximum EN/SET to Input Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Value
Units
-0.3 to 6.0
-0.3 to 6.0
-0.3 to 6.0
0.3
150
-40 to 150
V
V
V
V
mA
°C
Value
Units
160
625
°C/W
mW
Thermal Information3
Symbol
ΘJA
PD
Description
Thermal Resistance
Maximum Power Dissipation (TA = 25°C)4
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 6.25mW/°C above 25°C.
3122.2005.11.1.3
3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Electrical Characteristics1
VIN = 3.5V; CIN = COUT = C1 = C2 = 1.0µF; TA = -40°C to +85°C. Unless otherwise noted, typical values are
TA = 25°C.
Symbol
Description
Conditions
Input Power Supply
VIN
Operation Range
Icc
ISHDN
ID
Charge Pump
TSS
FCLK
ηCP
EN/SET
VEN(L)
VEN(H)
TLO
THI
TOFF
Input Current
Operating Current
Shutdown Current
Maximum Output Current
Min
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
Minimum EN/SET High Time
EN/SET Off Timeout
EN/SET Input Leakage
Max
Units
5.5
V
1.8
3.5
mA
120
1.0
132
µA
mA
2.7
3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
EN = 0
VIN = 3.5V; Code = 32
108
Soft-Start Time
Clock Frequency
Charge Pump Efficiency
Typ
VIN = 3.6V, IOUT(Total) = 120mA;
Measured from IN to OUT
VIN = 2.7V to 5.5V
VIN = 2.7V to 5.5V
200
1000
µs
kHz
93
%
0.5
1.4
0.3
75
50
-1.0
500
1.0
V
V
µs
ns
µs
µA
1. The AAT3122 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.
4
3122.2005.11.1.3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Typical Characteristics
Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C.
Efficiency vs. VIN
IDIODE vs. VIN
100
90
95
85
90
VDIODE = 3.3V
80
85
VDIODE = 3.4V
75
IDIODE (mA)
Efficiency (%)
(ID = 80mA)
80
75
VDIODE = 3.5V
70
65
VDIODE = 3.6V
VDIODE = 3.3V
VDIODE = 3.4V
70
65
60
55
50
60
55
45
50
40
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1 4.3
4.5
4.7 4.9
2.7
5.1
2.9
3.1
3.3
3.5
VIN (V)
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2.50
3.7
3.9
4.1
4.3
4.5
4.7
4.9
5.1
VIN (V)
VIH and VIL vs. VIN
Quiescent Current vs. VIN
Quiescent Current (mA)
VDIODE = 3.5V
VDIODE = 3.6V
0.850
0.825
0.800
0.775
VIH
0.750
VDIODE = 3.3V
0.725
VDIODE = 3.4V
0.700
VDIODE = 3.5V
0.675
VDIODE = 3.6V
0.650
VIL
0.625
0.600
3.00
3.50
4.00
VIN (V)
3122.2005.11.1.3
4.50
5.00
5.50
2.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
5
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Typical Characteristics
Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C.
Turn-On to Full-Scale Charge Pump
Turn-On to Full-Scale Load Switch
ENSET
(1V/div)
ENSET
(1V/div)
OUT
(2V/div)
OUT
(2V/div)
VDIODE
(1V/div)
VDIODE
(2V/div)
IIN
(200mA/div)
IIN
(100mA/div)
Time (50µs/div)
Time (50µs/div)
Load Switch to Charge Pump (80mA)
Charge Pump to Load Switch (80mA)
VIN
(10mV/div)
VIN
(20mV/div)
OUT
(2V/div)
OUT
(1V/div)
VDIODE
(2V/div)
VDIODE
(1V/div)
IIN
(100mA/div)
IIN
(200mV/div)
Time (50µs/div)
Time (50µs/div)
80mA Load Characteristics
Turn-Off
VIN
20mV/div
ENSET
(1V/div)
VDIODE
(2V/div)
OUT
IIN
(100mA/div)
VDIODE
Time (200µs/div)
6
Time (1µs/div)
3122.2005.11.1.3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Functional Block Diagram
VIN
Soft Start
1.5X
Charge
Pump
1MHz
Oscillator
Voltage
Reference
EN/SET
S2Cwire
Interface
5
32x8 bit
ROM
8
Current
Mode
DAC
C1+
C1C2+
C2OUT
D
GND
Functional Description
input and output voltages) and does not require user
intervention to maintain maximum efficiency.
The AAT3122 is a dual mode load switch (1X) and
high efficiency (1.5X) fractional charge pump device
intended for white LED backlight applications. The
fractional charge pump consists of a low dropout linear voltage regulator followed by a 1.5X charge
pump. To maximize power conversion efficiency, an
internal feedback control sensing circuit monitors
the voltage required on the constant current source
output. This control circuit then sets the load switch
and charge pump functions based upon the input
voltage level versus the output voltage level needed.
This function significantly enhances overall device
efficiency when the input voltage level is greater
than the voltage required at the constant current
source output. Switchover between the 1.5X
(charge pump) operating mode and the 1X (load
switch) mode occurs automatically (as a function of
The AAT3122 requires only four external components: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
ceramic capacitor for CIN, and one 0.33µF to 1µF
ceramic capacitor for COUT. The LDO/1.5X charge
pump output is converted into a constant current
output capable of driving up to six individual LEDs
with a maximum of 20mA each. The current source
output magnitude is controlled by the EN/SET serial data S2Cwire interface. The interface records rising edges of the EN/SET pin and decodes them into
32 individual current level settings each 1dB apart.
This is summarized in Figure 1 and Table 1. Code
32 is full scale, and Code 1 is full scale attenuated
by 31dB. The modulo 32 interface wraps states
back to State 1 after the 32nd clock.
3122.2005.11.1.3
7
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
EN/SET Serial Interface
Applications Information
The current source output magnitude is controlled
by the EN/SET serial interface. The interface
records rising edges of the EN/SET pin and
decodes them into 32 individual current level settings each 1dB apart. Code 32 is full scale, and
Code 1 is full scale attenuated by 31dB. The modulo 32 interface wraps states back to State 1 after
the 32nd clock, so 1dB of attenuation is achieved
by clocking the EN/SET pin 31 times. The counter
can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of
EN/SET enables the IC and initially sets the output
LED current to 3.3mA, the lowest setting. Once the
final clock cycle is input for the desired brightness
level, the EN/SET pin is held high to maintain the
device output current at the programmed level. The
device is disabled 500µs after the EN/SET pin transitions to a logic low state.
Current Level Settings
LED current level is set via the serial interface
according to a logarithmic scale, where each code
is 1dB greater than the previous code. In this manner, the LED brightness appears linear with each
increasing code. Table 1 depicts the relationship
between each rising edge of the EN/SET and the
output current in mA.
Code
IOUT (mA)
Code
IOUT (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
3.3
3.8
4.2
4.7
5.2
6.1
6.6
7.5
8.5
9.4
10.8
11.8
13.6
15.1
16.9
18.8
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
21.2
24.0
26.8
30.1
33.9
38.1
42.4
47.5
53.6
60.2
67.3
75.8
84.7
95.1
106.8
120.0
The EN/SET timing is designed to accommodate a
wide range of data rates. After the first rising edge
of EN/SET, the charge pump is enabled and reaches full capacity after the soft-start time (TSS). During
the soft-start time, multiple clock pulses may be
entered on the EN/SET pin to set the final output
current level with a single burst of clocks.
Alternatively, the EN/SET clock pulses may be
entered one at a time to gradually increase the LED
brightness over any desired time period. A constant
current is sourced as long as EN/SET remains in a
logic high state. The current source outputs are
switched off after EN/SET has remained in a low
state for at least the TOFF timeout period.
Table 1: Current Level Settings.
Normalized Current to Full Scale
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Code
Figure 1: Normalized Current Level Settings.
8
3122.2005.11.1.3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
EN/SET Timing Diagram
tHI
tOFF
tLO
EN/SET
Code
OFF
1
LED Selection
The AAT3122 is specifically intended for driving white
LEDs. However, the device design will allow the
AAT3122 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 controlled output
current generated from a varying input voltage.
Device Switching Noise Performance
The AAT3122 operates at a fixed frequency of
approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of
cellular telephone handsets or other communication devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-topeak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solutions. The AAT3122 soft-start feature prevents
noise transient effects associated with inrush currents during start-up of the charge pump circuit.
Power Efficiency and Device
Evaluation
Due to the unique charge pump circuit architecture
and design of the AAT3122, it is very difficult to
measure efficiency in terms of a percent value
comparing input power over output power.
Since the AAT3122 output is purely a constant current source, it is difficult to measure the output voltage to derive an overall output power measurement. For any given application, white LED forward
voltage levels can differ, yet the output drive current will be maintained as a constant.
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
3122.2005.11.1.3
2
3
OFF
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.
Charge Pump Efficiency
The AAT3122 is a fractional charge pump. The efficiency (η) can be simply defined as a linear voltage regulator with an effective output voltage that is equal to
one and a half times the input voltage. Efficiency (η) for
an ideal 1.5X charge pump can typically be expressed
as the output power divided by the input power.
η=
POUT
PIN
In addition, with an ideal 1.5X charge pump, the
output current may be expressed as 2/3 of the
input current. The expression to define the ideal
efficiency (η) can be rewritten as:
η=
POUT
V
= (VOUT x IOUT)/(VIN x 1.5IOUT) = OUT
PIN
1.5VIN
η(%) = 100
⎛ VOUT ⎞
⎝1.5VIN⎠
For a charge pump with an output of 5 volts and a nominal input of 3.5 volts, the theoretical efficiency is 95%.
Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in close agreement for
output load conditions from 3.0mA to 120mA. Efficiency
will decrease as load current drops below 0.05mA or
when the level of VIN approaches VOUT. Refer to the
Typical Characteristics section for measured plots of
efficiency versus input voltage and output load current
for the given charge pump output voltage options.
9
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
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 ESR ceramic capacitors are used. In
general, low ESR may be defined as less than
100mΩ. When choosing the four capacitors, a
capacitor value of 1µF is a good starting point. If
the LED current sources are only programmed for
light current levels, then the capacitor size may be
decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT3122 products. Ceramic capacitors
offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a
smaller PCB footprint, and is non-polarized. Low
ESR ceramic capacitors help maximize charge
pump transient response. Since ceramic capacitors
are non-polarized, they are not prone to incorrect
connection damage.
Equivalent Series Resistance: ESR is an important characteristic to consider when selecting a
capacitor. ESR is a resistance internal to a capac-
10
itor 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: Ceramic capacitors
less than 0.1µF are typically made from NPO or
C0G materials. NPO and C0G materials typically
have tight tolerance and are stable over temperature. Large capacitor values are typically composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors, typically greater
than 2.2µF, are often available in low-cost Y5V and
Z5U dielectrics, but large capacitors are not
required in the AAT3122 application.
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.
Thermal Protection
The AAT3122 has a thermal protection circuit that
will shut down the charge pump and current outputs if the die temperature rises above the thermal
limit due to short-circuit conditions.
3122.2005.11.1.3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Additional Application Circuit
VIN
C1+
C1
1µF
C1C2+
VOUT
VBATTERY
CIN
COUT
1µF
1µF
AAT3122
C2D1
EN/SET
C2
1µF
D1
D2
D3
D4
D5
D6
R B*
RB*
RB*
RB*
RB*
RB*
EN/SET
GND
*In some applications, white LED forward voltages (VF) can vary significantly. Ballast resistors between the LED cathodes and ground are
recommended for balancing the forward voltage differences. The ballast resistor value may be approxiamted by the following equation:
RB =
(VIN(MIN))1.5 - (VF(MAX) + 250mV)
IF(MAX)
VF(MAX) = Maximum expected LED forward voltage at the given maximum forward current level. Refer to the LED manufacturers’
datasheet for maximum VF specifications.
IF(MAX) = Maximum forward current used to drive an individual LED.
VIN(MIN) = Minimum input supply voltage for the application.
RB = Ballast resistor value in ohms.
3122.2005.11.1.3
11
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
JEXYY
AAT3122ITP-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.
Package Information
TSOPJW-12
2.85 ± 0.20
2.40 ± 0.10
0.10
0.20 +- 0.05
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
7° NOM
0.04 REF
0.055 ± 0.045
0.15 ± 0.05
+ 0.10
1.00 - 0.065
0.9625 ± 0.0375
3.00 ± 0.10
4° ± 4°
0.45 ± 0.15
0.010
2.75 ± 0.25
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
subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
12
3122.2005.11.1.3
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