Analogic AAT2845IML-EE-T1 Four-channel backlight driver with dual ldo Datasheet

AAT2845
Four-Channel Backlight Driver with Dual LDOs
General Description
Features
The AAT2845 is a highly integrated power solution
for single-cell lithium-ion-based LCD display applications. It includes a four-channel LED backlight
driver and two integrated 200mA LDOs as additional power supplies for display and camera-related chipsets.
•
•
The backlight driver is a low noise, constant frequency charge pump DC/DC converter that uses a
tri-mode load switch (1X), fractional (1.5X), and
doubling (2X) conversion to maximize efficiency.
Each of the four channels is capable of driving up
to 20mA per channel.
Input Voltage Range: 2.7V to 5.5V
Four-Channel LED Driver:
— Tri-Mode Charge Pump
— Up to 20mA/Channel
— Easy Control with Single Wire Interface
— 16 Current Levels
— Four Low Current Settings Down to 50µA
— Low IQ (50µA) for Low Current Mode
— >90% Peak Efficiency
Dual 200mA LDOs
Automatic Soft-Start
Over-Temperature Protection
Available in 3x4mm TQFN34-20 Package
-40°C to +85°C Temperature Range
•
•
•
•
•
AnalogicTech's S2Cwire™ (Simple Serial Control™)
serial digital input is used to enable, disable, and
set current for each LED with 16 available settings
down to 50µA. The low current mode supply current
can be as low as 50µA to save power and maintain
high efficiency.
ChargePump™
Applications
•
•
•
•
Each LED output is equipped with built-in protection for short-circuit and auto-disable functions.
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.
Camera Function Power Supplies
Camera Phone Displays
LCD Modules
White LED Backlighting
The AAT2845 is available in a Pb-free, thermallyenhanced 20-pin 3x4mm TQFN package.
Typical Application
CF1
1µF
C1-
CF2
1µF
C1+ C2-
IN
C2+
OUT
AAT2845
VBAT
3.6V
CIN
2.2µF
COUT
1µF
D1
D2
D3
D4
IN
LDOA
200mA
Co1
FBA
S2Cwire Backlight Control
EN/SET
LDO Enable
ENLDO
CBYP
0.1µF
2845.2006.12.1.0
LDOB
200mA
Co2
CBP
GND
FBB
1
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Pin Descriptions
Pin #
Symbol
1
2
3
4
D2
D1
LDOB
IN
5
6
PGND
IN
7
8
9
10
11
FBA
LDOA
C2C2+
OUT
12
13
14
15
16
17
18
19
20
C1C1+
EN/SET
ENLDO
D4
D3
GND
CBP
FBB
EP
Function
Current sink input #2.
Current sink input #1.
Output of LDO B. Connect a 2.2µF or larger ceramic capacitor to ground.
Input power supply for charge pump. Requires a 1µF or larger ceramic capacitor connected
between this pin and ground.
Power ground.
Input power pin for both LDOs. Connect a 1µF or larger ceramic capacitor from this pin to
PGND.
Feedback pin of LDO A. Regulated at 1.2V.
Output of LDO A. Connect a 2.2µF or larger ceramic capacitor to ground.
Flying capacitor 2 negative terminal.
Flying capacitor 2 positive terminal. Connect a 1µF ceramic capacitor between C2+ and C2-.
Charge pump output to drive load circuit. Connect a 1µF or larger ceramic capacitor between
this pin and PGND.
Flying capacitor 1 negative terminal.
Flying capacitor 1 positive terminal. Connect a 1µF ceramic capacitor between C1+ and C1-.
S2Cwire control pin for backlighting.
Enable pin for LDO A and B.
Current sink input #4.
Current sink input #3.
Ground.
Bypass pin for the internal reference.
Feedback pin of LDO B. Regulated at 1.2V. Connect a 0.1µF ceramic capacitor from this pin
to GND.
Exposed paddle (bottom); connect to PGND as closely as possible to the device.
Pin Configuration
TQFN34-20
(Top View)
D3
GND
CBP
FBB
17
18
19
20
D2
D1
LDOB
IN
PGND
IN
1
16
2
15
3
14
4
13
5
12
6
11
D4
ENLDO
EN/SET
C1+
C1OUT
9
10
8
7
C2+
C2LDOA
FBA
2
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AAT2845
Four-Channel Backlight Driver with Dual LDOs
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol
TJ
TLEAD
Description
IN, OUT, D1,D2, D3, D4 Voltage to AGND
C1+, C1-, C2+, C2- Voltage to GND
LDOA, LDOB, FBA, FBB, EN/SET, ENLDO, CBP
Voltage to AGND
PGND Voltage to GND
Operating Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to VOUT +0.3
V
V
-0.3 to VIN +0.3
V
-0.3 to +0.3
-40 to 150
300
V
°C
°C
Value
Units
50
2
°C/W
W
Thermal Information2, 3, 4
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation
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. Derate 20mW/°C above 40°C ambient temperature.
4. Mounted on an FR4 circuit board.
2845.2006.12.1.0
3
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Electrical Characteristics1
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
Symbol
Power Supply
VIN
ISHDN
Description
Input Voltage
Total Shutdown Current at VIN
and LDOIN
Conditions
Min
Typ
2.7
EN/SET = ENLDO = GND
Max Units
5.5
V
1.0
µA
Charge Pump
ICC
IDX
I(D-Match)
Operating Current
Average Current Accuracy
Current Matching2
1X to 1.5X or 1.5X to 2X Transition
VTH
Threshold at Any DX Pin
TSS
Soft-Start Time
FCLK
Clock Frequency
Over-Temperature Shutdown
TSD
Threshold
Over-Temperature Shutdown
THYS
Hysteresis
EN/SET Logic Control
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 Timeout
TLAT
EN/SET Latch Timeout
IEN/SET
EN/SET Input Leakage
1X Mode, 3.0 ≤ VIN ≤ 5.5,
Active, No Load Current
1.5X Mode, 3.0 ≤ VIN ≤ 5.5,
Active, No Load Current
2X Mode, 3.0 ≤ VIN ≤ 5.5,
Active, No Load Current
50µA Setting, 1X Mode
20mA Setting, TA = 25°C
1mA Setting, TA = 25°C
VIN - VF = 1.5V
1.0
3.0
5.0
18
0.9
50
20
1.0
0.5
µA
22
1.1
1.0
%
mV
100
1
µs
MHz
140
°C
15
°C
75
50
-1
mA
150
0.3
VEN/SET = VIN = 5V
mA
75
500
500
1
µs
ns
µs
µs
µs
µA
1. The AAT2845 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. Current matching is defined as the deviation of any sink current from the average of all active channels.
4
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Electrical Characteristics1
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
Symbol
Description
Conditions
Min
Typ
Max Units
LDOs
IIN
IN Operating Current
ENLDO = IN, EN/SET = AGND,
No Load
IOUT = 1mA to 200mA
IOUT = 150mA
VFB
Feedback Voltage
VDO
Dropout Voltage
ΔVOUT/
Line Regulation
VIN = (VOUT + 1V) to 5.0V
VOUT*ΔVIN
PSRR
Power Supply Rejection Ratio
IOUT =10mA, 1kHz
LDO Logic Control
EN/SET, ENLDO Pins Logic
VIL
Low Threshold
EN/SET, ENLDO Pins Logic High
VIH
Threshold
1.17
80
150
µA
1.2
150
1.23
300
V
mV
0.09
%/V
50
dB
0.4
1.4
V
V
1. The AAT2845 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.
2845.2006.12.1.0
5
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
Backlight Efficiency vs. Supply Voltage
Turn-On to 1X Mode
(VIN = 4.2V; 20mA/ch Load)
100
Efficiency (%)
90
20mA/ch
80
EN/SET
(2V/div)
VOUT
(2V/div)
70
60
1mA/ch
50
14.7mA/ch
40
30
VSINK
(1V/div)
IIN
(100mA/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
Supply Voltage (V)
Time (100µs/div)
Turn-On to 1.5X Mode
Turn-On to 2X Mode
(VIN = 3.5V; 20mA/ch Load)
(VIN = 2.8V; 20mA/ch Load)
EN/SET
(2V/div)
EN/SET
(2V/div)
VOUT
(2V/div)
VOUT
(2V/div)
VSINK
(500mV/div)
IIN
(500mA/div)
VSINK
(1V/div)
IIN
(200mA/div)
Time (100µs/div)
Time (100µs/div)
Turn-Off from 1.5X Mode Backlight
(30mA/ch; Data 1)
EN
(2V/div)
VDIODE
(2V/div)
IIN
(200mA/div)
Time (100µs/div)
6
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
Backlight Operating Characteristic
Backlight Operating Characteristic
(VIN = 2.9V; 2X Mode; 14mA/ch Load)
(VIN = 2.9V; 2X Mode; 20mA/ch Load)
VIN
(20mV/div)
VIN
(20mV/div)
VCP
(40mV/div)
VCP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
Time (500ns/div)
Time (500ns/div)
Backlight Operating Characteristic
Backlight Operating Characteristic
(VIN = 3.5V; 1.5X Mode; 14mA/ch Load)
(VIN = 3.7V; 1.5X Mode; 20mA/ch Load)
VIN
(20mV/div)
VIN
(20mV/div)
VCP
(40mV/div)
VCP
(40mV/div)
VSINK
(20mV/div)
VSINK
(20mV/div)
Time (500ns/div)
Time (500ns/div)
EN/SET Off Timeout vs. Supply Voltage
500
400
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
Supply Voltage (V)
2845.2006.12.1.0
EN/SET Off Timeout (µs)
EN/SET Latch Timeout (µs)
EN/SET Latch Timeout vs. Supply Voltage
450
400
350
-40°C
300
250
200
150
100
25°C
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
Supply Voltage (V)
7
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
EN/SET Low Threshold Voltage
vs. Supply Voltage
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
EN/SET High Threshold Voltage (V)
EN/SET Low Threshold Voltage (V)
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
EN/SET High Threshold Voltage
vs. Supply Voltage
1
-40°C
0.9
0.8
0.7
0.6
25°C
0.5
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
Supply Voltage (V)
Supply Voltage (V)
LDOA Turn-On Characteristic
LDOB Turn-On Characteristic
ENLDO
(2V/div)
ENLDO
(2V/div)
VOUT
(500mV/div)
VOUT
(500mV/div)
Time (50µs/div)
Time (50µs/div)
LDOs A and B Line Regulation
LDOs A and B Load Regulation
(10mA Load)
0.4
1.0
0.3
0.8
0.6
0.1
OUTA
0.0
-0.1
OUTB
-0.2
0.4
0.2
OUTA
0.0
-0.2
-0.4
-0.6
-0.3
OUTB
-0.8
-0.4
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)
8
Error (%)
Error (%)
0.2
-1.0
0.1
1
10
100
1000
Load Current (mA)
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
LDOA Line Transient Response
LDOB Line Transient Response
(10mA Load)
(10mA Load)
VIN
(400mV/div)
VIN
(400mV/div)
VIN = 4.2V
VIN = 4.2V
VIN = 3.7V
VIN = 3.7V
VOUT
(10mV/div)
VOUT
(10mV/div)
Time (40µs/div)
Time (40µs/div)
LDOA Load Transient Response
LDOB Load Transient Response
IOUT
(100mA/div)
IOUT
(100mA/div)
VOUT
(100mV/div)
VOUT
(100mV/div)
Time (20µs/div)
2845.2006.12.1.0
Time (20µs/div)
9
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Functional Block Diagram
C1+
C1- C2+
C2-
Tri-Mode
(1X, 1.5X and 2X)
Charge Pump
IN
OUT
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
S2Cwire
Interface
EN/SET
IN
LDO A
ENLDO
CBP
6x16
Bit ROM
D/A
D1
D/A
D2
D/A
D3
D/A
D4
LDOA
FBA
1.2V
Reference
LDO B
LDOB
FBB
GND
Functional Description
ceramic input capacitor (CIN), and one 0.33µF to
1µF ceramic charge pump output capacitor (COUT).
The AAT2845 is an integrated solution for LCD display applications with a built-in driver for white LED
backlight and two LDO voltage regulators for logic
power supplies.
The four constant current sink inputs (D1 to D4)
can drive four individual LEDs with a maximum current of 20mA each. The unused sink inputs must be
connected to the OUT pin; otherwise the part will
operate only in 2X charge pump mode. The
S2Cwire serial interface enables the charge pump
and sets the current sink magnitudes.
The backlight driver is a tri-mode load switch (1X)
and high-efficiency (1.5X or 2X) charge pump
device. 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 charge pump is enabled when any of the
four current sink inputs nears dropout. The charge
pump initially starts in 1.5X mode. If the charge
pump output droops enough for any current source
output to become close to dropout, the charge
pump will automatically transition to 2X mode. The
charge pump requires only four external components: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
10
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are
set via the S2Cwire serial interface according to a
logarithmic scale for the first 12 codes, and a separate low-current scale for the last four codes.
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 current level is programmable, no PWM
(pulse width modulation) or additional control cir-
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
cuitry is 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.
becomes active and the internal data register is
reset to zero. For subsequent current level programming, the number of rising edges corresponding to the desired code must be applied on the
EN/SET pin. When the EN/SET pin is held low for
an amount of time longer than TOFF (500µs), the
AAT2845 enters shutdown mode and draws less
than 1µA from the input. An internal data register is
reset to zero during shutdown.
The last four codes of the current level scale
engage a reduced quiescent current mode that
enhances the low-current setting efficiency. This
mode is especially useful for low-current applications where a continuous, low-current state is
maintained for a substantial length of time.
Auto-Disable Feature
S2Cwire Serial Interface
The current sink magnitude is controlled by
AnalogicTech's S2Cwire serial digital input. The
interface records rising edges of the EN/SET pin
and decodes them into 16 different states. The 16
current level settings available are indicated in
Table 1.
Data
Output
(mA/Ch)
Data
Output
(mA/Ch)
1
2
3
4
5
6
7
8
20
18.9
18.0
17.0
15.7
14.8
10.2
8.0
9
10
11
12
13
14
15
16
6.0
4.2
2.9
2.0
1.0
0.53
0.10
0.05
The charge pump in the AAT2845 is equipped with
an auto-disable feature for each LED channel. After
the IC is enabled and started up, a test current of
100µA (typical) is forced through each sink channel. The channel will be disabled if the voltage of
that particular DX pin does not drop to a certain
threshold. This feature is convenient for disabling
an unused channel or during an LED fail-short
event.
Low Dropout Regulators
The AAT2845 includes two LDO linear regulators.
The regulators run from the same 2.7V to 5.5V input
voltage as the charge pump. The regulators use a
single on/off control input, ENLDO. The LDO output
voltages are set through a resistive voltage divider
from the output (OUTA or OUTB) to the feedback
input (FBA or FBB). The ratio of resistor values
determines the LDO output voltage. The low 200mV
dropout voltage at 200mA load current allows the
regulator to maintain output voltage regulation.
Each LDO regulator can supply a continuous load
current up to 200mA. Both LDOs include current
limiting and thermal overload protection to prevent
damage to the load or to the LDOs.
Table 1: Current Level Settings.
The S2Cwire serial interface has flexible timing.
Data can be clocked-in at speeds higher than
1MHz, or much slower, such as 15kHz. After data
is applied, EN/SET is held high to latch the data.
Once EN/SET has been held in the logic high state
for time TLAT (500µs), the programmed current
2845.2006.12.1.0
Thermal Protection
The charge pump has a built-in thermal protection
circuit that will shut down the charge pump and the
LDOs if the die temperature rises above the thermal limit, as is the case during a short-circuit of the
OUT pin.
11
AAT2845
Four-Channel Backlight Driver with Dual LDOs
T HI
T LO
TOFF
TLAT
EN/SET
1
2
n-1
n ≤ 16
0
Data Reg
n-1
0
Figure 1: S2Cwire Serial Interface Timing.
Applications Information
LED Selection
The AAT2845 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT2845 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to
4.7V. LED applications may include mixed arrangements for display backlighting, color (RGB) LEDs,
infrared (IR) diodes, and any other load needing a
constant current source generated from a varying
input voltage. Since the D1 to D4 constant current
sinks are matched with negligible voltage dependence, the constant current channels will be matched
regardless of the specific LED forward voltage (VF)
levels.
The low dropout current sinks in the AAT2845 maximize performance and make it capable of driving
LEDs with high forward voltages. Multiple channels
can be combined to obtain a higher LED drive current without complication.
Device Switching Noise Performance
The AAT2845 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 AAT2845 soft-start feature prevents
noise transient effects associated with inrush currents during start-up of the charge pump circuit.
12
Shutdown
Since the sink switches are the only power returns
for all loads, there is no leakage current when all of
the sink switches are disabled. To activate the shutdown mode, hold the EN/SET input low for longer
than TOFF (500µs). In this state, the AAT2845 typically draws less than 1µA from the input. Data and
address registers are reset to 0 in shutdown.
LDO Output Voltage Programming
The output voltages for LDOA and LDOB are programmed by an external resistor divider network.
As shown below, the selection of R1 and R2 is a
straightforward matter.
R1 is chosen by considering the tradeoff between
the feedback network bias current and resistor
value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance, whereas lower resistor values increase bias
current and decrease efficiency.
OUTA
(OUTB)
VOUT
R2
FBA
(FBB)
VREF = 1.2V
R1
Figure 2: Selection of External Resistors.
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
To select appropriate resistor values, first choose
R1 such that the feedback network bias current is
reasonable. Then, according to the desired VOUT,
calculate R2 according to the equation below. An
example calculation follows.
R1 is chosen to be 120K, resulting in a small feedback network bias current of 1.2V/120K = 10µA.
The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below.
R2 =
R1(VOUT - 1.2)
1.2
The result is R2 = 60K. Since 60K is not a standard
1% value, 60.4K is selected. From this example
calculation, for VOUT = 1.8V, use R1 = 120K and R2
= 60.4K. A table of example output voltages and
corresponding resistor values is provided below.
R2 Standard 1% Values (R1 = 120K)
Ω)
VOUT (V)
R2 (Ω
2.8
2.5
2.0
1.8
1.5
160K
130K
79.6K
60.4K
30.1K
Table 2: Example Output Voltages and
Corresponding Resistor Values
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 AAT2845 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 outputs 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 or 2X charge pump mode. Each of these
modes will yield different efficiency values. Refer
to the following two sections for explanations for
each operational mode.
1X Mode Efficiency
The AAT2845 1X mode is operational at all times
and functions alone to enhance device power conversion efficiency when VIN is higher than the voltage across the load. When in 1X mode, voltage
conversion efficiency is defined as output power
divided by input power:
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following sections accounts only for efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT2845, it is very
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT2845 outputs are pure constant current sinks and typically drive individual loads, it is
difficult to measure the output voltage for a given
output (D1 to D4) 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.
2845.2006.12.1.0
η=
POUT
PIN
The expression to define the ideal efficiency (η)
can be rewritten as:
η=
POUT VOUT · IOUT VOUT
=
=
PIN
VIN · IOUT
VIN
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ VIN ⎠
13
AAT2845
Four-Channel Backlight Driver with Dual LDOs
1.5X and 2X Charge Pump Mode
Efficiency
The AAT2845 contains a fractional charge pump
which will boost the input supply voltage in the
event where VIN is less than the voltage required to
supply the output. The efficiency (η) 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 (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=
VOUT · IOUT
VOUT
POUT
=
=
PIN
VIN · 1.5IOUT 1.5VIN
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ 1.5VIN⎠
For a charge pump with an output of 5V and a nominal input of 3.5V, 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 1mA to
100mA. Efficiency will decrease substantially as
load current drops below 1mA or when the level of
VIN approaches VOUT.
The same calculations apply for 2X mode, where
the output current then becomes 1/2 of the input
current.
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 per14
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.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with
the AAT2845. 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 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
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., larger than 2.2µF) are often available in lowcost Y5V and Z5U dielectrics, but capacitors larger
than 1µF are not typically required for AAT2845
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.
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Evaluation Board Layout
Figure 3: AAT2845 Evaluation Board
Top Layer.
Evaluation Board User Interface
The user interface for the AAT2845 evaluation
board is provided by three buttons and two connection terminals. The board is operated by supplying
external power and pressing individual buttons or
button combinations. The table below indicates the
function of each button or button combination.
To power-on the evaluation board, connect a
power supply or battery to the DC- and DC+ terminals. Close the board's supply connection by positioning the J1 jumper to the ON position. A red LED
indicates that power is applied.
The evaluation board is made flexible so that the
user can disconnect the enable lines from the
Button(s) Pushed1
DATA
LIGHT
LIGHT+DATA
ENLDO
DATA+LIGHT+ENLDO
Figure 4: AAT2845 Evaluation Board
Bottom Layer.
microcontroller and apply external enable signals.
By removing the jumpers from J2, and/or J3, external enable signals can be applied to the board.
External enable signals must be applied to the ON
pin of each J2, or J3 terminal.
When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages should not exceed the supply voltage that is applied to the IN pins of the
device (DC+).
The LDO loads can be connected directly to the
evaluation board. For adequate performance, be
sure to connect the load between OUTA/OUTB
and DC- as opposed to some other GND in the
system.
Description
Increment the backlight data setting. Hold down the button to auto-cycle through
the brightness levels.
Toggle ON/OFF the backlighting section. Set the brightness level using the DATA
button.
Decrement the backlight data setting. Hold down to auto-cycle.
Toggle ON/OFF the LDOs.
Reset. Clear data and bring all enable lines low.
Table 3: Evaluation Board User Interface.
1. The "+" indicates that these buttons are pressed and released together.
2845.2006.12.1.0
15
AAT2845
Four-Channel Backlight Driver with Dual LDOs
DC+
1
2
VOUT
3
J1
C9
100µF
D1
D2
D3
D4
Optional 100µF capacitor
to bypass lab supply
C7
0.1µF
D3
D4
16
ENLDO
15
EN/SET
14
IN
C1+
13
5
PGND
C1-
12
6
IN
OUTCP
11
7
8
9
ENL
EN/SET
C1 1.0µF
C3
1.0µF
C2+
C4
2.2µF
U1
AAT2845
4
C2-
R11
120K
C6
2.2µF
LDOB
17
GND
FBB
R10
160K
D1
3
LDOA
Programmed for 2.8V output
D2
2
18
FBA
OUTB
1
19
CBYP
20
10
C2
1.0µF
R8
60.4K
C5
2.2µF
OUTA
Programmed for 1.8V output
R9
120K
Figure 5: AAT2845 Section Schematic.
16
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
R6
220
J2
EN/SET
3
2
1
R7
100K
VIN
VIN
R1 R2 R3
1K 1K 1K
U2
1
2
3
4
DATA
SW1
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
C8
1µF
8
7
6
5
LED7
RED
PIC12F675
LIGHT
R5
330
SW2
ENLDO
J3
SW3
ENL
3
2
1
R4
100K
DC-
Figure 6: MCU Section Schematic.
Evaluation Board Component Listing
Component
U1
U2
D1 - D4
C1 - C3
C4 - C6
C7
C8
C9
R1 - R3
R4, R7
R5
R6
R8
R9, R11
R10
J1 - J3
LED7
SW1 - SW3
2845.2006.12.1.0
Part#
Description
AAT2845IML-EE-T1
PIC12F675
LW M673
GRM18x
GRM18x
GRM18x
GRM31x
TAJBx
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PRPN401PAEN
CMD15-21SRC/TR8
PTS645TL50
Four-Channel Backlight Driver with Dual LDOs
8-bit CMOS, FLASH MCU; 8-pin PDIP
Mini TOPLED White LED; SMT
1.0µF, 10V, X5R, 0603, ceramic
2.2µF, 10V, X5R, 0603, ceramic
0.1µF, 16V, X7R, 0603, ceramic
1µF, 10V, X5R, 1206, ceramic
100µF, 10V, 10µA, tantalum
1K, 5%, 1/4W; 1206
100K, 5%, 1/4W; 1206
330, 5%, 1/4W; 1206
220, 5%, 1/4W; 1206
60.4K, 1%, 1/10W; 0603
120K, 1%, 1/10W; 0603
160K, 1%, 1/10W; 0603
Conn. Header, 2mm zip
Red LED; 1206
Switch Tact, SPST, 5mm
Manufacturer
AnalogicTech
Microchip
OSRAM
Murata
Murata
Murata
Murata
AVX
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Sullins Electronics
Chicago Miniature Lamp
ITT Industries
17
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TQFN34-20
UHXYY
AAT2845IML-EE-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 Information3
TQFN34-20
3.00 ± 0.05
1.55 ± 0.05
2.55 ± 0.05
4.00 ± 0.05
Detail "A"
Top View
Bottom View
0.425 ± 0.05
0.75 ± 0.05
7.5° ± 7.5°
0.021 ± 0.004
0.5 BSC
Side View
0.23 ± 0.06
0.025 ± 0.025
Detail "A"
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.
18
2845.2006.12.1.0
AAT2845
Four-Channel Backlight Driver with Dual LDOs
© 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
warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. 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.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737- 4600
Fax (408) 737- 4611
2845.2006.12.1.0
19
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