Analogic AAT1231ITP-1-T1 Step-up dc/dc converters for white led backlight application Datasheet

AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
General Description
Features
The AAT1231/1231-1 are high frequency, high efficiency constant current boost converters capable of
24V maximum output voltage. Both devices are
ideal power solutions for backlight applications with
up to six white LEDs in series or up to twelve white
LEDs in a parallel/series configuration. The input
voltage is 2.7V to 5.5V for single-cell lithiumion/polymer (Li-ion) based portable devices.
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The LED current is digitally controlled across a 6x
operating range using AnalogicTech’s Simple Serial
Control™ (S2Cwire™) interface. Programmability
across 26 discrete current steps provides high resolution, low noise, flicker-free, constant LED outputs.
In programming AAT1231 operation, LED brightness
increases based on the data received at the EN/SET
pin. In programming AAT1231-1 operation, LED
brightness decreases based on the data received at
the EN/SET pin. The SEL logic pin changes the feedback voltage between two programmable ranges.
The AAT1231 and the AAT1231-1 feature high current
limit and fast, stable transitions for stepped or pulsed
current applications. The high switching frequency (up
to 2MHz) provides fast response and allows the use
of ultra-small external components, including chip
inductors and capacitors. Fully integrated control circuitry simplifies design and reduces total solution size.
The AAT1231 and the AAT1231-1 offer a true load
disconnect feature which isolates the load from the
power source while in the OFF or disabled state. This
eliminates leakage current, making the devices ideally suited for battery-powered applications.
The AAT1231 and the AAT1231-1 are available in Pbfree, thermally-enhanced 12-pin TSOPJW packages.
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SwitchReg™
Input Voltage Range: 2.7V to 5.5V
Maximum Continuous Output 24V @ 50mA
Drives 6 LEDs in Series, 12 LEDs in Parallel/
Series Configuration
— Constant LED Current with 6% Accuracy
Digital Control with S2Cwire Single Wire Interface
— 26 Discrete Steps
— No PWM Control Required
— No Additional Circuitry
Up to 82% Efficiency
Up to 2MHz Switching Frequency Allows
Small External Chip Inductor and Capacitors
Hysteretic Control
— No External Compensation Components
— Excellent Load Transient Response
— High Efficiency at Light Loads
Integrated Soft Start with No External Capacitor
True Load Disconnect Guarantees <1.0µA
Shutdown Current
Selectable Feedback Voltage Ranges for
High Resolution Control of Load Current
Short-Circuit, Over-Voltage, and OverTemperature Protection
12-Pin TSOPJW Package
-40°C to +85°C Temperature Range
Applications
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Digital Still Cameras (DSCs)
Mobile Handsets
MP3 Players
PDAs and Notebook PCs
White LED Drivers
Typical Application
L = 2.2µH
C1
2.2µF
LIN
VIN
SW
PGND
Li-Ion:
VIN = 2.7V to 4.2V
Select
R3
12kΩ
Capable of Driving
Six LEDs in Series
(see Applications Section)
FB
AGND
OSRAM
LW M678
C2
2.2µF
EN/SET
SEL
Up to 24V/
50mA max
R2
226kΩ
OVP
AAT1231/
1231-1
Enable/Set
1231.2007.01.1.2
PVIN
DS1
R1 (RBALLAST)
30.1Ω
1
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Pin Descriptions
Pin #
Symbol
1
PVIN
2
3
EN/SET
SEL
4
5
6, 7
8
9
10
11
12
VIN
N/C
SW
PGND
AGND
FB
OVP
LIN
Function
Input power pin; connected to the source of the P-channel MOSFET. Connect to the
input capacitor(s).
IC enable pin and S2Cwire input control to set output current.
FB voltage range select.
For the AAT1231, a logic LOW sets the FB voltage range from 0.1V to 0.4V; a logic
HIGH sets the FB voltage range from 0.3V to 0.6V.
For the AAT1231-1, a logic LOW sets the FB voltage range from 0.4V to 0.1V; a logic
HIGH sets the FB voltage range from 0.6V to 0.3V.
Input voltage for the converter. Connect directly to the PVIN pin.
No connection.
Boost converter switching node. Connect the power inductor between this pin and LIN.
Power ground for the boost converter.
Ground pin.
Feedback pin. Connect a resistor to ground to set the maximum LED current.
Feedback pin for over-voltage protection sense.
Switched power input. Connect the power inductor between this pin and SW.
Pin Configuration
TSOPJW-12
(Top View)
PVIN
EN/SET
SEL
VIN
N/C
SW
2
1
12
2
11
3
10
4
9
5
8
6
7
LIN
OVP
FB
AGND
PGND
SW
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Part Number Descriptions
SEL Polarity
Part Number
HIGH
LOW
S2C Feedback
Voltage Programming
AAT1231ITP
AAT1231ITP-1
0.3V ≤ VFB ≤ 0.6V
0.6V ≥ VFB ≥ 0.3V
0.1V ≤ VFB ≤ 0.4V
0.4V ≥ VFB ≥ 0.1V
See Table 2
See Table 3
Absolute Maximum Ratings1
TA = 25°C unless otherwise noted.
Symbol
PVIN, VIN
SW
LIN, EN/SET,
SEL, FB
TJ
TS
TLEAD
Description
Value
Units
Input Voltage
Switching Node
-0.3 to 6.0
28
V
V
Maximum Rating
VIN + 0.3
V
-40 to 150
-65 to 150
300
°C
°C
°C
Value
Units
160
625
°C/W
mW
Operating Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Thermal Information
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.
1231.2007.01.1.2
3
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Electrical Characteristics1
TA = -40°C to +85°C unless otherwise noted. Typical values are at 25°C, VIN = 3.6V.
Symbol
Power Supply
PVIN, VIN
VOUT(MAX)
IQ
ISHDN
IOUT
ΔVLINEREG(FB)/
ΔVIN
RDS(ON) L
RDS(ON) IN
TSS
VOVP
ILIMIT
TSD
THYS
SEL, EN/SET
VSEL(L)
VSEL(H)
VEN/SET(L)
VEN/SET(H)
TEN/SET (LO)
TEN/SET(HI)
TOFF
TLAT
IEN/SET
AAT1231
FB
Description
Conditions
Input Voltage Range
Maximum Output Voltage
Operating Current
Shutdown Current
Maximum Continuous Output
Current2
SEL = GND, FB = 0.1V
EN/SET = GND
Line Regulation
VIN = 2.7V to 5.5V, VFB = 0.6V
Min
2.7
40
2.7V < VIN < 5.5V, VOUT = 24V
Low Side Switch On Resistance
Input Disconnect Switch
On Resistance
From Enable to Output Regulation;
VFB = 300mV
Over-Voltage Protection Threshold VOUT Rising
Over-Voltage Hysteresis
VOUT Falling
N-Channel Current Limit
TJ Thermal Shutdown Threshold
TJ Thermal Shutdown Hysteresis
Soft-Start Time
SEL Threshold Low
SEL Threshold High
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
EN/SET Input Leakage
FB Pin Regulation
Typ
1.1
Max
Units
5.5
24
70
1.0
V
V
µA
µA
50
mA
0.7
%/V
80
mΩ
180
mΩ
300
µs
1.2
100
2.5
140
15
1.3
V
mV
A
°C
°C
0.4
V
V
V
V
µs
µs
µs
µs
µA
1.4
0.4
VEN/SET
VEN/SET
VEN/SET
VEN/SET
VEN/SET
<
>
<
>
=
0.6V
1.4V
0.6V
1.4V
5V VIN = 5V
VIN = 2.7V to 5.5V, SEL = GND,
EN/SET = HIGH
VIN = 2.7V to 5.5V, SEL = HIGH,
EN/SET = DATA16
1.4
0.3
75
75
500
500
1
-1
0.09
0.1
0.11
0.564
0.6
0.636
0.09
0.1
0.11
V
AAT1231-1
FB
FB Pin Regulation
VIN = 2.7V to 5.5V, SEL = GND,
EN/SET = DATA16
VIN = 2.7V to 5.5V, SEL = HIGH,
EN/SET = HIGH
V
0.564
0.6
0.636
1. Specification over the -40°C to +85°C operating temperature range is assured by design, characterization, and correlation with statistical process controls.
2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and thermal limitations.
4
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Typical Characteristics
Efficiency vs. LED Current
Efficiency vs. LED Current
(4 White LEDs; RBALLAST = 30.1Ω
Ω)
(5 White LEDs; RBALLAST = 30.1Ω
Ω)
85
83
VIN = 5V
82
83
Efficiency (%)
Efficiency (%)
84
82
81
80
VIN = 4.2V
VIN = 3.6V
79
78
VIN = 5V
81
80
VIN = 4.2V
79
VIN = 3.6V
78
77
76
77
75
2
4
6
8
10
12
14
16
18
20
2
4
6
LED Current (mA)
12
14
16
18
20
18
20
Efficiency vs. LED Current
(6 White LEDs; RBALLAST = 30.1Ω
Ω)
(12 White LEDs; RBALLAST = 30.1Ω
Ω)
84
81
80
83
VIN = 5V
79
78
VIN = 4.2V
77
76
VIN = 3.6V
75
VIN = 5V
82
Efficiency (%)
Efficiency (%)
10
LED Current (mA)
Efficiency vs. LED Current
81
80
79
VIN = 4.2V
78
77
VIN = 3.6V
76
74
75
73
74
2
4
6
8
10
12
14
16
18
20
2
4
6
LED Current (mA)
10
12
14
16
Feedback Voltage vs. Temperature
(RBALLAST = 30.1Ω
Ω)
(EN = GND)
700
Feedback Voltage (mV)
1.0
0.8
0.6
85°C
0.4
25°C
0.2
0.0
2.7
8
LED Current (mA)
Shutdown Current vs. Input Voltage
Shutdown Current (µA)
8
-40°C
600
500
400
300
200
100
0
3.1
3.5
3.9
4.3
Input Voltage (V)
1231.2007.01.1.2
4.7
5.1
5.5
-40
-15
10
35
60
85
Temperature (°C)
5
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Typical Characteristics
Accuracy ILED vs. Temperature
Accuracy ILED vs. Input Voltage
(VFB = 0.6V; RBALLAST = 30.1Ω
Ω)
1.0
2.0
0.8
1.5
Accuracy ILED (%)
Accuracy ILED (%)
(VFB = 0.6V; RBALLAST = 30.1Ω
Ω)
0.5
0.3
0.0
-0.3
-0.5
1.0
-40°C
0.5
0.0
-0.5
25°C
-1.0
-1.5
-0.8
-2.0
-1.0
-40
-15
10
35
60
85
2.7
3.2
20.2
5.2
5.7
0.8
0.6
0.4
2.5V
0V
0.6
0.4
0.2
0
0.5
0.0
Time (50µs/div)
Inductor Current (A) (bottom)
20.4
Enable Voltage (V) (top)
Feedback Voltage (V) (middle)
Shutdown
(VFB = 0.6V; ILED = 20mA)
20.6
Time (50µs/div)
Output Ripple
Output Ripple
(6 White LEDs; ILED = 13mA)
(6 White LEDs; ILED = 20mA)
VOUT (DC
Offset 20.7V)
(20mV/div)
VOUT (DC
Offset 19.8V)
(50mV/div)
20
VLX (V)
0
20
0
0.5
0.5
IL (A)
4.7
Line Transient
3.6V
VLX (V)
4.2
(6 White LEDs; RBALLAST = 30.1Ω)
4.2V
20.8
3.7
Input Voltage (V)
Feedback Voltage (bottom) (V)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Temperature (°C)
IL (A)
0
Time (400ns/div)
6
85°C
0
Time (200ns/div)
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
AAT1231 Soft Start
(6 White LEDs; VFB = 0.6V)
(6 White LEDs; VFB = 0.3V)
0V
0.4
0.2
0
2
1
0
2.5V
0V
0.2
0
2
1
0
Time (100µs/div)
Time (50µs/div)
AAT1231-1 Soft Start with S2Cwire
AAT1231-1 Soft Start
(6 White LEDs; VFB = 0.6V)
0V
0.4
0.2
0
1
0
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
2.5V
2.5V
0.6
0V
0.4
0.2
0
1
0
Time (50µs/div)
Time (100µs/div)
Transition of LED Current
(6 White LEDs; SEL = Low; ILED = 3.3mA to 13.3mA)
20
18
0.4
0.3
0.2
0.1
0.0
Time (20µs/div)
1231.2007.01.1.2
22
20
18
0.4
0.3
0.2
0.1
0.0
Feedback Voltage (bottom) (V)
22
Output Voltage (top) (V)
Transition of LED Current
(6 White LEDs; SEL = Low; ILED = 13.3mA to 6.6mA)
Feedback Voltage (bottom) (V)
Output Voltage (top) (V)
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
(6 White LEDs; VFB = 0.3V)
0.6
Inductor Current (bottom) (A)
2.5V
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
AAT1231 Soft Start with S2Cwire
Inductor Current (bottom) (A)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
Typical Characteristics
Time (20µs/div)
7
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Typical Characteristics
EN/SET Off Timeout vs. Input Voltage
300
350
300
EN/SET Off Timeout (µs)
EN/SET Latch Timeout (µs)
EN/SET Latch Timeout vs. Input Voltage
25°C
-40°C
250
85°C
200
150
100
-40°C
250
200
85°C
150
100
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
Input Voltage (V)
4.7
5.1
5.5
1.2
1.1
1.1
-40°C
1.0
0.9
0.8
0.7
85°C
25°C
0.6
-40°C
1.0
VIH (V)
VIL (V)
4.3
EN/SET High Threshold vs. Input Voltage
1.2
0.9
25°C
0.8
85°C
0.7
0.6
0.5
0.5
0.4
2.7
3.1
3.5
3.9
4.3
4.7
5.1
0.4
2.7
5.5
3.1
3.5
Input Voltage (V)
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Low Side Switch On Resistance
vs. Input Voltage
Input Disconnect Switch Resistance
vs. Input Voltage
160
300
280
120°C
120
RDS(ON)IN (mΩ
Ω)
140
RDS(ON)L (mΩ)
3.9
Input Voltage (V)
EN/SET Low Threshold vs. Input Voltage
100°C
100
80
25°C
60
85°C
2.5
3
3.5
120°C
260
4
4.5
Input Voltage (V)
5
5.5
6
100°C
240
220
200
180
25°C
160
40
8
25°C
140
2.5
3
85°C
3.5
4
4.5
5
5.5
6
Input Voltage (V)
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Functional Block Diagram
LIN
PVIN
VIN
OVP
EN/SET
FB
SW
Reference
Output
Select
Control
SEL
AGND
PGND
Functional Description
age overshoot across the full input voltage range
and all loading conditions.
The AAT1231 and the AAT1231-1 consist of a
DC/DC boost controller, an integrated slew rate
controlled input disconnect MOSFET switch, and a
high voltage MOSFET power switch. A high voltage
rectifier, power inductor, output capacitor, and
sense resistors are required to implement a DC/DC
constant current boost converter. The input disconnect switch is activated when a valid input voltage
is present and the EN/SET pin is pulled high. The
slew rate control on the P-channel MOSFET
ensures minimal inrush current as the output voltage is charged to the input voltage, prior to the
switching of the N-channel power MOSFET.
Monotonic turn-on is guaranteed by the integrated
soft-start circuitry. Soft-start eliminates output volt-
The maximum current through the LED string is set
by the ballast resistor and the feedback voltage of
the IC. The output current may be programmed by
adjusting the level of the feedback reference voltage which is programmed through the S2Cwire
interface. The SEL pin selects one of two feedback
voltage ranges. For the AAT1231 and with a LOW
logic level applied to the SEL pin, the FB pin voltage can be programmed from 0.1V to 0.4V. With a
logic HIGH applied to the SEL pin, the FB pin voltage can be programmed from 0.3V to 0.6V. In the
AAT1231-1, the SEL function is inverted in that the
FB pin voltage can be programmed from 0.4V to
0.1V with a logic LOW applied to the SEL pin and
0.6V to 0.3V with a logic HIGH applied to the SEL
1231.2007.01.1.2
9
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
pin. Regardless of which device is chosen, the
feedback voltage can be set to any one of 16 current levels within each FB range, providing highresolution control of the LED current, using the single-wire S2Cwire control.
grammed current source connected to the output
capacitor, parallel with the LED string and ballast
resistor. There is no right-half plane zero, and
loop stability is achieved with no additional compensation components.
For torch and flash applications where a short
duration, pulsed load is desired, applying a lowto-high transition on the AAT1231's SEL pin produces a 1.5x to 3.0x LED current step. In the
AAT1231-1 on the other hand, the LED current
step for a low-to-high transition on the SEL pin
can be programmed from 3.0x to 1.5x. In both
products, the step size is determined by the programmed voltage at the FB pin where the internal
default setting is 3.0x in the AAT1231 and 1.5x in
the AAT1231-1.
An increase in the feedback voltage (VFB) results
in an increased error signal sensed across the
ballast resistor (R1). The controller responds by
increasing the peak inductor current, resulting in
higher average current in the inductor and LED
string(s). Alternatively, when the VFB is reduced,
the controller responds by decreasing the peak
inductor current, resulting in lower average current in the inductor and LED string(s).
Control Loop
The AAT1231/1231-1 provide the benefits of current mode control with a simple hysteretic output
current loop providing exceptional stability and
fast response with minimal design effort. The
device maintains exceptional constant current
regulation, transient response, and cycle-by-cycle
current limit without additional compensation
components.
The AAT1231/1231-1 modulate the power MOSFET switching current to maintain the programmed FB voltage. This allows the FB voltage
loop to directly program the required inductor current in order to maintain the desired LED current.
The switching cycle initiates when the N-channel
MOSFET is turned ON and current ramps up in
the inductor. The ON interval is terminated when
the inductor current reaches the programmed
peak current level. During the OFF interval, the
input current decays until the lower threshold, or
zero inductor current, is reached. The lower current is equal to the peak current minus a preset
hysteresis threshold, which determines the inductor ripple current. The peak current is adjusted by
the controller until the LED output current requirement is met.
The magnitude of the feedback error signal determines the average input current. Therefore, the
AAT1231/1231-1 controller implements a pro-
10
Under light load conditions, the inductor OFF interval current goes below zero and the boost converter enters discontinuous mode operation. Further
reduction in the load current results in a corresponding reduction in the switching frequency. The
AAT1231/1231-1 provide pulsed frequency operation which reduces switching losses and maintains
high efficiency under light load conditions.
Operating frequency varies with changes in the
input voltage, output voltage, and inductor size.
Once the boost converter has reached continuous
mode, further increases in the LED current will not
significantly change the operating frequency. A
small 2.2µH (±20%) inductor is selected to maintain high frequency switching (up to 2MHz) and
high efficiency operation for outputs up to 24V.
Soft Start / Enable
The input disconnect switch is activated when a
valid input voltage is present and the EN/SET pin
is pulled high. The slew rate control on the Pchannel MOSFET ensures minimal inrush current
as the output voltage is charged to the input voltage, prior to switching of the N-channel power
MOSFET. Monotonic turn-on is guaranteed by the
built-in soft-start circuitry. Soft start eliminates
output current overshoot across the full input voltage range and all loading conditions.
After the soft start sequence has terminated, the
initial LED current is determined by the internal,
default FB voltage across the external ballast resistor at the FB pin. Additionally, the AAT1231 and the
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
AAT1231-1 have been designed to offer the system designer two choices for the default FB voltage
based on the state of the SEL pin. Changing the
LED current from its initial default setting is easy by
using the S2Cwire single wire serial interface; the
FB voltage can be increased (as in the AAT1231;
see Table 2) or decreased (as in the AAT1231-1;
see Table 3) relative to the default FB voltage.
Current Limit and Over-Temperature
Protection
The switching of the N-channel MOSFET terminates when a current limit of 2.5A (typical) is
exceeded. This minimizes power dissipation and
component stresses under overload and short-circuit conditions. Switching resumes when the current decays below the current limit.
Application Information
Over-Voltage Protection
OVP Protection with Open Circuit Failure
The OVP protection circuit consists of a resistor
network tied from the output voltage to the OVP pin
(see Figure 1). To protect the device from open circuit failure, the resistor divider can be selected
such that the over-voltage threshold occurs prior to
the output reaching 24V (VOUT(MAX)). The value of
R3 should be selected from 10kΩ to 20kΩ to minimize losses without degrading noise immunity.
R2 = R 3 ·
Thermal protection disables the AAT1231/1231-1
when internal dissipation becomes excessive.
Thermal protection disables both MOSFETs. The
junction over-temperature threshold is 140°C with
15°C of temperature hysteresis. The output voltage
automatically recovers when the over-temperature
fault condition is removed.
⎛ VOUT(MAX) ⎞
-1
⎝ VOVP
⎠
VOUT
AAT1231/1231-1
R2
COUT
OVP
R3
GND
Over-Voltage Protection
Internal bias of all circuits is controlled via the VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all internal circuitry prior to soft start.
1231.2007.01.1.2
Over Voltage Protection Pin (top) (V)
Inductor Current (bottom (A)
Under-Voltage Lockout
Figure 1: Over-Voltage Protection Circuit.
1.224V
1.168V
26
24
22
2
1
0
Output Voltage (middle) (V)
Over-voltage protection prevents damage to the
AAT1231/1231-1 during open-circuit or high output
voltage conditions. An over-voltage event is
defined as a condition where the voltage on the
OVP pin exceeds the Over-Voltage Threshold Limit
(VOVP = 1.2V typical). When the voltage on the
OVP pin has reached the threshold limit, the converter stops switching and the output voltage
decays. Switching resumes when the voltage on
the OVP pin drops below the lower hysteresis limit,
maintaining an average output voltage between the
upper and lower OVP thresholds multiplied by the
resistor divider scaling factor.
Time (5ms/div)
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
11
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Assume R3 = 12kΩ and VOUT(MAX) = 24V. Selecting
1% resistor for high accuracy, this results in R2 =
226kΩ (rounded to the nearest standard value).
The minimum OVP threshold can be calculated:
VOUT(OVP_MIN) = VOVP(MIN) ·
⎛ R2
⎞
+1
⎝ R3
⎠
= 21.8V
To avoid OVP detection and subsequent reduction
in the programmed output current (see following
section), the maximum operating voltage should
not exceed the minimum OVP set point.
VOUT(MAX) < VOUT(OVP_MIN)
ensure DC current and negligible flicker in the LED
string(s).
The waveform in Figure 3 shows the output voltage
and LED current at cold temperature with a six
series white LED string and VOVP = 19.4V. As
shown, the output voltage rises as a result of the
increased VFLED which triggers the OVP constant
voltage operation. Self heating of the LEDs triggers a smooth transition back to constant current
control.
OVP Constant Voltage Operation
Cold Temperature Applied
ILED
(10mA/div)
In some cases, this may disallow configurations
with high LED forward voltage (VFLED) and/or
greater than five series white LEDs. VFLED unit-tounit tolerance can be as high as +15% of nominal
for white LED devices.
OVP Constant Voltage Operation
Under closed loop constant current conditions, the
output voltage is determined by the operating current, LED forward voltage characteristics (VFLED),
quantity of series connected LEDs (N), and the
feedback pin voltage (VFB).
VOUT = VFB + N · VFLED
When the rising OVP threshold is exceeded,
switching is stopped and the output voltage
decays. Switching automatically restarts when the
output drops below the lower OVP hysteresis voltage (100mV typical) and, as a result, the output
voltage increases. The cycle repeats, maintaining
an average DC output voltage proportional to the
average of the rising and falling OVP levels (multiplied by the resistor divider scaling factor). High
operating frequency and small output voltage ripple
12
Self-Recovery
VOUT
(5V/div)
ΔILED
Time (1s/div)
Figure 3: Over-Voltage Protection
Constant Voltage Operation
(6 White LEDs; ILED = 13mA;
Ω; R3 = 12kΩ
Ω).
R2 = 182kΩ
While OVP is active, the maximum LED current
programming error (ΔILED) is proportional to voltage
error across an individual LED (ΔVFLED).
ΔVFLED =
(N · VFLED(MAX) - VOUT(OVP_MIN) - VFB)
N
To minimize the ΔILED error, the minimum OVP voltage (VOUT(OVP_MIN)) may be increased, yielding a
corresponding increase in the maximum OVP voltage (VOUT(OVP_MAX)). Measurements should confirm
that the maximum switching node voltage
(VSW(MAX)) is less than 28V under worst-case operating conditions.
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
VSW(MAX) = VOVP(MAX) ·
⎛ R3
⎞
+ 1 + VF + VRING
⎝ R2
⎠
VF = Schottky Diode DS1 forward voltage at turnOFF
VRING = Voltage ring occurring at turn-OFF
LED Selection and Current Setting
The AAT1231/1231-1 are well suited for driving
white LEDs with constant current. Applications
include main and sub-LCD display backlighting,
and color LEDs.
The LED current is controlled by the FB voltage
and the ballast resistor. For maximum accuracy, a
1% tolerance resistor is recommended.
The ballast resistor (RBALLAST) value can be calculated as follows:
RBALLAST =
VFB(MAX)
ILED(MAX)
Typical white LEDs are driven at maximum continuous currents of 15mA to 20mA. For maximum
output, two parallel strings of six series LEDs are
used. A total output current of 30mA or 40mA is
required (15mA to 20mA in each string). The
maximum quantity of series connected LEDs is
determined by the minimum OVP voltage of the
boost converter (VOUT(OVP_MIN)), minus the maximum feedback voltage (VFB(MAX)) divided by the
maximum LED forward voltage (V FLED(MAX)).
VFLED(MAX) can be estimated from the manufacturers’ datasheet at the maximum LED operating
current.
VOUT(OVP_MIN) = VOVP(MIN) ·
N=
(VOUT(OVP_MIN) - VFB(MAX))
VFLED(MAX)
Figure 4 shows the schematic of using six LEDs in
series. Assume VFLED @ 20mA = 3.5V (typical)
from LW M673 (OSRAM) datasheet.
where:
VFB(MAX) = 0.4V when SEL = Low
VFB(MAX) = 0.6V when SEL = High
VOUT(OVP_MIN) = 1.1V ·
i.e., for a maximum LED current of 20mA (SEL =
High):
N=
RBALLAST =
⎛ R2
⎞
+1
⎝ R3
⎠
VFB
0.6
=
= 30Ω ≈ 30.1Ω
ILED(MAX)
0.020
Ω)
RBALLAST (Ω
Maximum ILED
Current (mA)
SEL = High
SEL = Low
50
40
35
30
25
20
15
10
5
12.1
15.0
16.9
20.0
24.3
30.1
40.2
60.4
121.0
8.06
10.0
11.3
13.3
16.2
20.0
26.7
40.2
80.6
⎛ 226kΩ
⎞
+ 1 = 21.82V
⎝ 12kΩ
⎠
21.82V - 0.6V
3.5V
≈ 6.1
Therefore, under typical operating conditions, six
LEDs can be used in series.
Table 1: Maximum LED Current and RBALLAST
Resistor Values (1% Resistor Tolerance).
1231.2007.01.1.2
13
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
VIN = 2.7V to 5.5V
JP1
1
R4 10K
2
C1
2.2µF
DS1
L1
3
Enable
JP2
2.2µH
U1 AAT1231/1231-1
1
2
3
4
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
VOUT = 24V/20mA
R2
226K
12
11
10
R3
12K
9
8
7
TSOP12JW
1
2
3
Select
R1
D6
D5
30.1Ω
LED
LED
D1
LED
D2
LED
D3
LED
C2
2.2µF
D4
LED
U1 AAT1231/1231-1 TSOPJW-12
L1 2.2µH SD3814-2R2
C1 2.2µF 10V 0603
C2 2.2µF 25V 0805
D1-D6 LW M673 White LED
DS1 30V 0.2A BAT42W SOD-123
R1 30.1 0603
R2 226K 0603
R3 12K 0603
R4 10K 0603
Figure 4: AAT1231/1231-1 White LED Boost Converter Schematic.
LED Brightness Control
14
LED Current (mA)
The AAT1231 and the AAT1231-1 use S2Cwire programming to control LED brightness and does not
require PWM (pulse width modulation) or additional control circuitry. 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 output current of the
AAT1231 and the AAT1231-1 can be changed successively to brighten or dim the LEDs in smooth
transitions (i.e., to fade out) or in abrupt steps, giving the user complete programmability and realtime control of LED brightness.
25
20
SEL = HIGH
15
10
(Default)
SEL = LOW
5
0
1
4
7
10
13
16
S2Cwire Data Register
Figure 5: Programming AAT1231 LED Current
Ω.
with RBALLAST = 30.1Ω
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
3. 5
Select Pin Scaling Factor
(Low to High)
25
LED Current (mA)
20
SEL=HIGH
(Default)
15
10
SEL=LOW
5
0
1
4
7
10
13
16
(Default)
1. 5
1. 0
4
7
10
13
16
Figure 8: AAT1231-1 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
Alternatively, toggling the SEL logic pin from low to
high implements stepped or pulsed LED currents by
increasing the FB pin voltage. Figures 7 and 8 illustrate the SELECT pin scaling factor, defined as the
LED current with SEL=HIGH divided by the LED
current with SEL=LOW. For the AAT1231, scaling
factors from 1.5x to 3.0x are possible, depending on
the S2Cwire data register (default = 3.0x). In the
AAT1231-1, the possible scaling factors are 3.0x to
1.5x with the internal default setting of 1.5x.
S2Cwire Serial Interface
AnalogicTech's S2Cwire single wire serial interface
is a proprietary high-speed single-wire interface
available only from AnalogicTech. The S2Cwire
interface records rising edges of the EN/SET input
and decodes them into 16 individual states. Each
state corresponds to a reference feedback voltage
setting on the FB pin, as shown in Table 2.
S2Cwire Serial Interface Timing
3.5
Select Pin Scaling Factor
(High to Low)
2. 0
S2Cwire Data Register
Figure 6: Programming AAT1231-1 LED
Ω.
Current with RBALLAST = 30.1Ω
(Default)
3.0
2.5
2.0
1.5
1.0
4
7
10
13
16
S2Cwire Data Register
Figure 7: AAT1231 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
1231.2007.01.1.2
2. 5
1
S2Cwire Data Register
1
3. 0
The S2Cwire single wire serial interface data can be
clocked-in at speeds up to 1MHz. After data has
been submitted, EN/SET is held high to latch the
data for a period TLAT. The FB pin voltage is subsequently changed to the level as defined by the state
of the SEL logic pin. When EN/SET is set low for a
time greater than TOFF, the AAT1231/1231-1 is disabled. When either the AAT1231 or the AAT1231-1
is disabled, the register is reset to its default value.
In the AAT1231, the default register value sets the
FB pin voltage to 0.6V if the EN/SET pin is subsequently pulled HIGH. In the AAT1231-1, the FB pin
voltage is set to 0.3V under the same condition.
15
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
S2Cwire Feedback Voltage
Programming
edges applied at the EN/SET pin determine the FB
pin voltage. If a logic LOW is applied at the SEL pin,
the default feedback voltage range for the AAT1231
is 0.1V to 0.4V; for a logic HIGH condition at the
SEL pin, the default feedback voltage range is 0.3V
to 0.6V. Conversely, if a logic LOW is applied at the
SEL pin of the AAT1231-1, the default feedback
voltage range becomes 0.4V to 0.1V and 0.6V to
0.3V for a logic HIGH condition at the SEL pin.
The FB pin voltage is set to the default level at initial powerup. The AAT1231 and the AAT1231-1 are
programmed through the S2Cwire interface. Table 2
illustrates FB pin voltage programming for the
AAT1231 and Table 3 illustrates FB pin voltage programming for the AAT1231-1. The rising clock
THI
TLO
TOFF
T LAT
EN/SET
1
Data Reg
2
n-1
n ≤ 16
0
n-1
0
Figure 9: AAT1231/1231-1 S2Cwire Timing Diagram to Program the Output Voltage.
Rising Clock
Edges/Data
Register
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
SEL = Low
Reference
LED Current (mA);
Ω
Voltage (V)
RBALLAST = 30.1Ω
SEL = High
Reference
LED Current (mA);
Ω
Voltage (V)
RBALLAST = 30.1Ω
0.1 (default)
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.34
0.36
0.38
0.40
0.3 (default)
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
0.48
0.50
0.52
0.54
0.56
0.58
0.60
3.32
3.99
4.65
5.32
5.98
6.64
7.31
7.97
8.64
9.30
9.97
10.63
11.30
11.96
12.62
13.29
9.97
10.63
11.30
11.96
12.62
13.29
13.95
14.62
15.28
15.95
16.61
17.28
17.94
18.60
19.27
19.93
Ω
Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1Ω
(Assume Nominal Values).
16
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Rising Clock
Edges/Data
Register
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
SEL = Low
Reference
LED Current (mA);
Ω
Voltage (V)
RBALLAST = 30.1Ω
Reference
Voltage (V)
0.4 (default)
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.6 (default)
0.58
0.56
0.54
0.52
0.50
0.48
0.46
0.44
0.42
0.40
0.38
0.36
0.34
0.32
0.30
13.29
12.62
11.96
11.30
10.63
9.97
9.30
8.64
7.97
7.31
6.64
5.98
5.32
4.65
3.99
3.32
SEL = High
LED Current (mA);
Ω
RBALLAST = 30.1Ω
19.93
19.27
18.60
17.94
17.28
16.61
15.95
15.28
14.62
13.95
13.29
12.62
11.96
11.30
10.63
9.97
Ω
Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1Ω
(Assumes Nominal Values).
Selecting the Schottky Diode
To ensure minimum forward voltage drop and no
recovery, high voltage Schottky diodes are considered the best choice for the AAT1231/1231-1 boost
converters. The output diode is sized to maintain
acceptable efficiency and reasonable operating
junction temperature under full load operating conditions. Forward voltage (VF) and package thermal
resistance (θJA) are the dominant factors to consider in selecting a diode. The diode non-repetitive
peak forward surge current rating (IFSM) should be
considered for high pulsed load applications, such
as camera flash. IFSM rating drops with increasing
conduction period. Manufacturers’ datasheets
should be consulted to verify reliability under peak
loading conditions. The diode's published current
rating may not reflect actual operating conditions
1231.2007.01.1.2
and should be used only as a comparative measure between similarly rated devices.
20V rated Schottky diodes are recommended for outputs less than 15V, while 30V rated Schottky diodes
are recommended for outputs greater than 15V.
The switching period is divided between ON and
OFF time intervals.
1
= TON + TOFF
FS
During the ON time, the N-channel power MOSFET
is conducting and storing energy in the boost inductor. During the OFF time, the N-channel power
MOSFET is not conducting. Stored energy is transferred from the input battery and boost inductor to
the output load through the output diode.
17
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Duty cycle is defined as the ON time divided by the
total switching interval.
Forward Current (mA)
D=
10000
TON
TON + TOFF
= TON ⋅ FS
B340LA
MBR0530T
1000
ZHCS350
100
BAT42W
10
0.00
The maximum duty cycle can be estimated from
the relationship for a continuous mode boost converter. Maximum duty cycle (DMAX) is the duty cycle
at minimum input voltage (VIN(MIN)).
DMAX =
0.10
0.30
0.40
0.50
0.60
0.70
Forward Voltage (V)
The average diode current is equal to the output
current.
IAVG(TOT) = IOUT
VOUT - VIN(MIN)
VOUT
The average diode current during the OFF time can
be estimated.
IAVG(OFF) =
0.20
The average output current multiplied by the forward diode voltage determines the loss of the output diode.
IOUT
1 - DMAX
PLOSS(DIODE) = IAVG(TOT) · VF
= IOUT · VF
The following curves show the VF characteristics
for different Schottky diodes (100°C case). The VF
of the Schottky diode can be estimated from the
average current during the off time.
For continuous LED currents, the diode junction
temperature can be estimated.
TJ(DIODE) = TAMB + θJA · PLOSS(DIODE)
Manufacturer
Diodes, Inc.
Diodes, Inc.
ON Semi
Zetex
Central Semi
Part
Number
Rated
Forward
Current (A)
Non-Repetitive
Peak Surge
Current (A)
Rated
Voltage (V)
Thermal
Resistance
θJA, °C/W)
(θ
Case
B340LA
BAT42W
MBR0530T
ZHCS350
CMDSH2-3
3
0.2
0.5
0.35
0.2
70.0
4.0
5.5
4.2
1.0
40
30
30
40
30
25
500
206
330
500
SMA
SOD-123
SOD-123
SOD-523
SOD-323
Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Levels.
18
1231.2007.01.1.2
AAT1231/1231-1
Output diode junction temperature should be maintained below 110ºC, but may vary depending on
application and/or system guidelines. The diode
θJA can be minimized with additional PCB area on
the cathode. PCB heat-sinking the anode may
degrade EMI performance. The reverse leakage
current of the rectifier must be considered to maintain low quiescent (input) current and high efficiency under light load. The rectifier reverse current
increases dramatically at elevated temperatures.
Switching Frequency (MHz)
Step-Up DC/DC Converters for
White LED Backlight Applications
2.0
VIN = 3.0V
VOUT = 18V
1.8
VIN = 3.0V
VOUT = 15V
1.6
VIN = 3.6V
VOUT = 18V
1.4
VIN = 3.6V
VOUT = 15V
1.2
1.0
0.8
0.6
VIN = 2.7V
VOUT = 18V
0.4
40
VIN = 2.7V
VOUT = 15V
50
60
70
80
90
100
Selecting the Boost Inductor
The AAT1231 and the AAT1231-1 controllers utilize
hysteretic control and the switching frequency
varies with output load and input voltage. The
value of the inductor determines the maximum
switching frequency of the boost converter.
Increased output inductance decreases the switching frequency, resulting in higher peak currents and
increased output voltage ripple. To maintain 2MHz
maximum switching frequency and stable operation, an output inductor sized from 1.5µH to 2.7µH
is recommended.
A better estimate of DMAX is possible once VF is
known.
DMAX =
(VOUT + VF - VIN(MIN))
(VOUT + VF)
Where VF is the Schottky diode forward voltage. If
not known, it can be estimated at 0.5V.
Manufacturer’s specifications list both the inductor
DC current rating, which is a thermal limitation, and
peak inductor current rating, which is determined
by the saturation characteristics. Measurements at
full load and high ambient temperature should be
completed to ensure that the inductor does not saturate or exhibit excessive temperature rise.
The output inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load
conditions. Peak current may be estimated using
the following equation, assuming continuous conduction mode. Worst-case peak current occurs at
minimum input voltage (maximum duty cycle) and
maximum load. Switching frequency (FS) can be
estimated from the curves and assumes a 2.2µH
inductor.
1231.2007.01.1.2
Switching Frequency (MHz)
Output Current (mA)
2.0
1.8
VIN = 3.0V
VOUT = 12V
1.6
VIN = 3.0V
VOUT = 10V
VIN = 3.6V
VOUT = 12V
VIN = 3.6V
VOUT = 10V
1.4
1.2
1.0
0.8
VIN = 2.7V
VOUT = 10V
0.6
0.4
40
50
VIN = 2.7V
VOUT = 12V
60
70
80
90
100
Output Current (mA)
IPEAK =
IOUT
D
· VIN(MIN)
+ MAX
(1 - DMAX)
(2 · FS · L)
At light load and low output voltage, the controller
reduces the operating frequency to maintain maximum operating efficiency. As a result, further
reduction in output load does not reduce the peak
current. Minimum peak current can be estimated
from 0.5A to 0.75A.
At high load and high output voltages, the switching frequency is somewhat diminished, resulting in
higher IPEAK. Bench measurements are recommended to confirm actual IPEAK and ensure that the
inductor does not saturate at maximum LED current and minimum input voltage.
The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components.
Under worst-case RMS conditions, the current
waveform is critically continuous. The resulting
RMS calculation yields worst-case inductor loss.
The RMS current value should be compared
against the manufacturer's temperature rise, or
thermal derating, guidelines.
19
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
IRMS =
(wound and gapped) inductors. In general, chiptype inductors have increased winding resistance
(DCR) when compared to shielded, wound varieties.
IPEAK
3
For a given inductor type, smaller inductor size leads
to an increase in DCR winding resistance and, in
most cases, increased thermal impedance. Winding
resistance degrades boost converter efficiency and
increases the inductor’s operating temperature.
Inductor Efficiency Considerations
The efficiency for different inductors is shown in
Figure 7 for six white LEDs in series. Smaller
inductors yield increased DCR and reduced operating efficiency.
80
To ensure high reliability, the inductor case temperature should not exceed 100ºC. In some cases,
PCB heatsinking applied to the LIN node (nonswitching) can improve the inductor's thermal
capability. PCB heatsinking may degrade EMI performance when applied to the SW node (switching)
of the AAT1231/1231-1.
Shielded inductors provide decreased EMI and may
be required in noise sensitive applications.
Unshielded chip inductors provide significant space
savings at a reduced cost compared to shielded
Manufacturer
Sumida
www.sumida.com
Cooper Electronics
www.cooperet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Efficiency (%)
PLOSS(INDUCTOR) = IRMS2 · DCR
77
Cooper SD3814-2R2 (77mΩ)
Cooper SD3110-2R2 (161mΩ)
74
71
Murata LQH2MCN2R2M02L (440mΩ)
68
65
2
5
8
11
14
17
20
LED Current (mA)
Figure 10: AAT1231/1231-1 Efficiency for
Different Inductor Types (VIN = 3.6V;
Six White LEDs in Series).
Part
Number
Inductance
(µH)
Maximum
DC ISAT
Current (mA)
DCR
Ω)
(mΩ
Size (mm)
LxWxH
Type
CDRH2D11-2R2
2.2
780
78
3.2x3.2x1.2
Shielded
SD3814-2R2
SD3110-2R2
2.2
2.2
1900
910
77
161
4.0x4.0x1.4
3.1x3.1x1.0
Shielded
Shielded
LQH2MCN2R2M02L
2.2
455
440
2.0x1.6x0.7
Shielded
NR3010T-2R2M
2.2
1100
95
3.0x3.0x1.0
CBC2016T2R2M
2.2
750
200
2.0x1.6x1.6
CBC2518T2R2M
2.2
510
90
2.5x1.8x1.8
Shielded
Chip
Non-Shielded
Shielded
Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT).
20
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Selecting the Boost Capacitors
To maintain stable operation at full load, the output
capacitor should be sized to maintain ΔVOUT
between 100mV and 200mV.
The high output ripple inherent in the boost converter necessitates low impedance output filtering.
The boost converter input current flows during both
ON and OFF switching intervals. The input ripple
current is less than the output ripple and, as a
result, less input capacitance is required.
Multi-layer ceramic (MLC) capacitors provide small
size and adequate capacitance, low parasitic
equivalent series resistance (ESR) and equivalent
series inductance (ESL), and are well suited for
use with the AAT1231/1231-1 boost regulator. MLC
capacitors of type X7R or X5R are recommended
to ensure good capacitance stability over the full
operating temperature range.
PCB Layout Guidelines
Boost converter performance can be adversely
affected by poor layout. Possible impact includes
high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every
attempt should be made to optimize the layout in
order to minimize parasitic PCB effects (stray resistance, capacitance, and inductance) and EMI coupling from the high frequency SW node. A suggested PCB layout for the AAT1231/1231-1 boost converter is shown in Figures 10 and 11. The following
PCB layout guidelines should be considered:
The output capacitor is sized to maintain the output
load without significant voltage droop (ΔVOUT) during the power switch ON interval, when the output
diode is not conducting. A ceramic output capacitor
from 2.2µF to 4.7µF is recommended (see Table 5).
Typically, 25V rated capacitors are required for the
24V maximum boost output. Ceramic capacitors
sized as small as 0805 are available which meet
these requirements.
1. Minimize the distance from Capacitor C1 and
C2 negative terminal to the PGND pins. This is
especially true with output capacitor C2, which
conducts high ripple current from the output
diode back to the PGND pins.
2. Minimize the distance between L1 to DS1 and
switching pin SW; minimize the size of the PCB
area connected to the SW pin.
3. Maintain a ground plane and connect to the IC
PGND pin(s) as well as the GND terminals of
C1 and C2.
4. Consider additional PCB area on DS1 cathode
to maximize heatsinking capability. This may
be necessary when using a diode with a high
VF and/or thermal resistance.
MLC capacitors exhibit significant capacitance
reduction with applied voltage. Output ripple measurements should confirm that output voltage droop
and operating stability are acceptable. Voltage derating can minimize this factor, but results may vary with
package size and among specific manufacturers.
Output capacitor size can be estimated at a switching frequency (FS) of 500kHz (worst case).
COUT =
Manufacturer
Murata
Murata
Murata
Murata
Murata
IOUT · DMAX
FS · ΔVOUT
Part Number
Value (µF)
Voltage Rating
Temp Co
Case Size
GRM188R60J225KE19
GRM188R61A225KE34
GRM219R61E225KA12
GRM21BR71E225KA73L
GRM21BR61E475KA12
2.2
2.2
2.2
2.2
4.7
6.3
10
25
25
25
X5R
X5R
X5R
X7R
X5R
0603
0603
0805
0805
0805
Table 6: Recommended Ceramic Capacitors.
1231.2007.01.1.2
21
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
AAT1231/1231-1
White LED
Driver
S2Cwire
Microcontroller
Figure 11: AAT1231/1231-1 Evaluation
Board Top Side Layout (with six LEDs
and microcontroller).
22
Figure 12: AAT1231/1231-1 Evaluation
Board Bottom Side Layout (with six LEDs
and microcontroller).
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
VCC
R7
1K
R8
330
R6
1K
R5
1K
D7
RED
1
3
5
Down
02
4
1
3
5
Select
02
4
1
3
5
C3
1µF
U2
1
02
4
Up
SW3
2
3
4
SW2
S2Cwire
Microcontroller
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
8
7
6
R9
330
5
PIC12F675
D8
GREEN
(Select indicator)
SW1
R4
10K
J2
DC-
J3
DC+
DS1
Schottky
L1
J1
1
2
3
2.2µH
U1
VCC
1
JP1
2
3
4
C1
2.2µF
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
VOUT
R2
226K
12
11
10
R3
12K
9
8
7
AAT1231/1231-1
R1
D6
D5
30.1Ω
LED
LED
D1
LED
AAT1231/1231-1
White LED
Driver
D2
LED
D3
LED
C2
2.2µF
D4
LED
U1 AnalogicTech AAT1231/1231-1 TSOPJW-12 package
U2 PIC12F675
C1 GRM188R60J225KE01
C2 GRM21BR71E225KA73
C3 GRM216R61A105KA01
R1 30.1Ω, 1%, 1/4W; 0603
R2 226kΩ, 1%, 1/4W; 0603
R3 12.1kΩ, 1%, 1/4W; 0603
R4 10kΩ, 5%, 1/4W; 0603
R5, R6, R7 1KΩ, 5%, 1/4W; 0805
R8, R9 330Ω, 5%, 1/4W; 0805
JP1 0Ω, 5%; 0805
DS1 BAT42W
L1 Cooper Electronics 2.2µH SD3814-2R2
D1-D6 White Hyper-Bright LED LW M673
D7 Red LED 1206
D8 Green LEC 1206
SW1 - SW3 SPST, 5mm
J1, J2, J3 Conn. Header, 2mm
Figure 13: AAT1231/1231-1 Evaluation Board Schematic (with six LEDs and microcontroller).
1231.2007.01.1.2
23
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Additional Applications
Efficiency vs. LED Current
L = 2.2µH
C1
2.2µF
PVIN
LIN
VIN
SW
R2
187kΩ
C2
2.2µF
OVP
R3
12kΩ
ENSET
SEL
85
FB
AGND
VIN = 5V
84
AAT1231/
1231-1
PGND
(4 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 24V/
50mA max
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
DS1
83
82
81
80
VIN = 4.2V
VIN = 3.6V
79
78
30.1Ω
20mA
77
2
4
6
8
10
12
14
16
18
20
18
20
LED Current (mA)
Figure 14: Four LEDs In Series Configuration.
Efficiency vs. LED Current
(5 White LEDs; RBALLAST = 30.1Ω
Ω)
L = 2.2µH
C1
2.2µF
LIN
VIN
SW
82
AAT1231/
1231-1
PGND
DS1
R2
196kΩ
OVP
R3
12kΩ
ENSET
SEL
AGND
83
C2
2.2µF
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
PVIN
Up to 24V/
50mA max
VIN = 5V
81
80
VIN = 4.2V
79
VIN = 3.6V
78
77
76
FB
30.1Ω
20mA
75
2
4
6
8
10
12
14
16
LED Current (mA)
Figure 15: Five LEDs In Series Configuration.
24
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Efficiency vs. LED Current
L = 2.2µH
C1
2.2µF
LIN
VIN
SW
(6 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 24V/
50mA max
81
AAT1231/
1231-1
R2
226kΩ
80
C2
2.2µF
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
PVIN
DS1
OVP
PGND
R3
12kΩ
EN/SET
SEL
AGND
FB
30.1Ω
VIN = 5V
79
78
VIN = 4.2V
77
76
VIN = 3.6V
75
74
20mA
73
2
4
6
8
10
12
14
16
18
20
LED Current (mA)
Figure 16: Six LEDs In Series Configuration.
L = 2.2µH
C1
2.2µF
PVIN
LIN
VIN
SW
Efficiency vs. LED Current
Up to 24V/
50mA max
(12 White LEDs; RBALLAST = 30.1Ω
Ω)
84
AAT1231/
1231-1
R2
226kΩ
83
C2
2.2µF
OVP
PGND
R3
12kΩ
EN/SET
SEL
AGND
FB
30.1Ω
VIN = 5V
82
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
DS1
81
80
79
VIN = 4.2V
78
77
VIN = 3.6V
76
20mA
75
30.1Ω
20mA
74
2
4
6
8
10
12
14
16
18
20
LED Current (mA)
Figure 17: Twelve LEDs In Series/Parallel Configuration.
1231.2007.01.1.2
25
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
TSOPJW-12
SDXYY
TUXYY
AAT1231ITP-T1
AAT1231ITP-1-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
+ 0.10
- 0.05
2.40 ± 0.10
0.20
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.
26
1231.2007.01.1.2
AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight 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 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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AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737- 4600
Fax (408) 737- 4611
1231.2007.01.1.2
27