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

PRODUCT DATASHEET
AAT1231
SwitchRegTM
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 singlecell lithium-ion/polymer (Li-ion) based portable devices.
• 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 Over-Temperature
Protection
• 12-Pin TSOPJW Package
• -40°C to +85°C Temperature Range
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 Pb-free,
thermally-enhanced 12-pin TSOPJW packages.
Applications
•
•
•
•
•
Digital Still Cameras (DSCs)
Mobile Handsets
MP3 Players
PDAs and Notebook PCs
White LED Drivers
Typical Application
L = 2.2μH
C1
2.2μF
VIN
SW
PGND
Li-Ion:
VIN = 2.7V to 4.2V
Select
DS1
C2
2.2μF
Capable of Driving
Six LEDs in Series
(see Applications Section)
FB
AGND
OSRAM
LW M678
R3
12kΩ
EN/SET
SEL
Up to 24V/
50mA max
R2
226kΩ
OVP
AAT1231/
1231-1
Enable/Set
1231.2008.06.1.5
PVIN
LIN
R1 (RBALLAST)
30.1Ω
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1
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Pin Descriptions
Pin #
Symbol
1
PVIN
2
EN/SET
3
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)
2
PVIN
1
12
LIN
EN/SET
2
11
OVP
SEL
3
10
FB
VIN
4
9
AGND
N/C
5
8
PGND
SW
6
7
SW
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1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Part Number Descriptions
SEL Polarity
Part Number
HIGH
LOW
S2Cwire 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
Input Voltage
Switching Node
Maximum Rating
Operating Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
28
VIN + 0.3
-40 to 150
-65 to 150
300
V
V
V
°C
°C
°C
Value
Units
160
625
°C/W
mW
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.
1231.2008.06.1.5
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3
PRODUCT DATASHEET
AAT1231
SwitchRegTM
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
Description
Typ
Max
Units
5.5
24
70
1.0
50
V
V
μA
μA
mA
SEL = GND, FB = 0.1V
EN/SET = GND
2.7V < VIN < 5.5V, VOUT = 24V
40
Line Regulation
VIN = 2.7V to 5.5V, VFB = 0.6V
0.7
%/V
2.7
80
mΩ
300
μs
Low Side Switch On Resistance
Soft-Start Time
VOVP
Over-Voltage Protection Threshold
Over-Voltage Hysteresis
N-Channel Current Limit
TJ Thermal Shutdown Threshold
TJ Thermal Shutdown Hysteresis
FB
Min
Input Voltage Range
Maximum Output Voltage
Operating Current
Shutdown Current
Maximum Continuous Output Current2
TSS
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
Conditions
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
From Enable to Output Regulation;
VFB = 300mV
VOUT Rising
VOUT Falling
1.1
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
0.564
0.6
0.636
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
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
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1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
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
4.7
5.1
5.5
Input Voltage (V)
1231.2008.06.1.5
-40
-15
10
35
60
85
Temperature (°C)
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5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
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)
3.6V
Enable Voltage (V) (top)
Feedback Voltage (V) (middle)
Shutdown
(VFB = 0.6V; ILED = 20mA)
20.4
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
20.6
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)
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PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Typical Characteristics
AAT1231 Soft Start
AAT1231 Soft Start with S2Cwire
(6 White LEDs; VFB = 0.3V)
0V
0.4
0.2
0
2
1
0
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
2.5V
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
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)
1231.2008.06.1.5
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)
0V
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)
Inductor Current (bottom) (A)
Enable Voltage (top) (V)
Feedback Voltage (middle) (V)
(6 White LEDs; VFB = 0.6V)
Time (20µs/div)
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PRODUCT DATASHEET
AAT1231
SwitchRegTM
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
5
5.5
6
100°C
240
220
200
180
25°C
160
40
140
2.5
Input Voltage (V)
8
25°C
3
85°C
3.5
4
4.5
5
5.5
6
Input Voltage (V)
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1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Functional Block Diagram
LIN
PVIN
VIN
OVP
EN/SET
SW
Control
FB
Reference
Output
Select
SEL
AGND
Functional Description
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. Softstart eliminates output voltage overshoot across the full
input voltage range and all loading conditions.
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
1231.2008.06.1.5
PGND
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 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 high-resolution control of the LED current,
using the single-wire S2Cwire control.
For torch and flash applications where a short duration,
pulsed load is desired, applying a low-to-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
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PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
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.
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 programmed 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.
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).
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 P-channel 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 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.
Some applications may require the output to be active
when a valid input voltage is present. In these cases,
add a 10kΩ resistor between the VIN, VP, and EN/SET
pins to avoid startup issues.
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1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Current Limit and
Over-Temperature Protection
Application Information
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.
Over-Voltage Protection
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.
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.
Over-Voltage Protection
R2 = R3 ·
Under-Voltage Lockout
AAT1231/1231-1
R2
COUT
OVP
R3
GND
Figure 1: Over-Voltage Protection Circuit.
1.224V
1.168V
26
24
22
2
1
0
Output Voltage (middle) (V)
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.
VOUT
Over Voltage Protection Pin (top) (V)
Inductor Current (bottom (A)
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.
⎛ VOUT(MAX) ⎞
-1
⎝ VOVP
⎠
Time (5ms/div)
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
1231.2008.06.1.5
www.analogictech.com
11
PRODUCT DATASHEET
AAT1231
SwitchRegTM
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) ·
OVP Constant Voltage Operation
Cold Temperature Applied
⎛ R2
⎞
+1
⎝ R3
⎠
ILED
(10mA/div)
= 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)
In some cases, this may disallow configurations with
high LED forward voltage (VFLED) and/or greater than five
series white LEDs. VFLED unit-to-unit 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 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.
12
Self-Recovery
VOUT
(5V/div)
ΔILED
Time (1s/div)
Figure 3: Over-Voltage Protection
Constant Voltage Operation
(6 White LEDs; ILED = 13mA;
R2 = 182kΩ; R3 = 12kΩ).
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 worstcase operating conditions.
VSW(MAX) = VOVP(MAX) ·
⎛ R3
⎞
+ 1 + VF + VRING
⎝ R2
⎠
VF = -Schottky Diode DS1 forward voltage at turn-OFF
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.
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
The ballast resistor (RBALLAST) value can be calculated as
follows:
RBALLAST =
VFB(MAX)
ILED(MAX)
where:
VFB(MAX) = 0.4V when SEL = Low
VFB(MAX) = 0.6V when SEL = High
i.e., for a maximum LED current of 20mA (SEL = High):
RBALLAST =
VFB
ILED(MAX)
VOUT(OVP_MIN) = VOVP(MIN) ·
0.6
=
= 30Ω ≈ 30.1Ω
0.020
N=
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
Table 1: Maximum LED Current and RBALLAST
Resistor Values (1% Resistor Tolerance).
1231.2008.06.1.5
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 (VFLED(MAX)). VFLED(MAX) can
be estimated from the manufacturers’ datasheet at the
maximum LED operating current.
⎛ R2
⎞
+1
⎝ R3
⎠
(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.
VOUT(OVP_MIN) = 1.1V ·
N=
⎛ 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.
www.analogictech.com
13
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
VIN = 2.7V to 5.5V
JP1
1
2
2
3
3
4
Enable
JP2
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
VOUT = 24V/20mA
2.2µH
U1 AAT1231/1231-1
R4 10K
1
C1
2.2µF
DS1
L1
R2
226K
12
11
10
R3
12K
9
8
7
2
3
Select
D2
LED
C2
2.2µF
D3
LED
TSOP12JW
1
D1
LED
D4
LED
R1
D6
D5
30.1Ω
LED
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
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 real-time
control of LED brightness.
LED Current (mA)
25
SEL = HIGH
15
10
(Default)
SEL = LOW
0
1
4
7
20
SEL=HIGH
(Default)
15
10
SEL=LOW
5
0
1
4
7
10
13
16
S2Cwire Data Register
Figure 6: Programming AAT1231-1 LED Current
with RBALLAST = 30.1Ω.
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.
20
5
LED Current (mA)
25
10
13
16
S2Cwire Data Register
Figure 5: Programming AAT1231 LED Current
with RBALLAST = 30.1Ω.
14
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
16 individual states. Each state corresponds to a reference feedback voltage setting on the FB pin, as shown
in Table 2.
Select Pin Scaling Factor
(High to Low)
3.5
(Default)
3.0
2.5
S2Cwire Serial Interface Timing
2.0
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.
1.5
1.0
1
4
7
10
13
16
S2Cwire Data Register
Figure 7: AAT1231 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
Select Pin Scaling Factor
(Low to High)
3. 5
3. 0
2. 5
S2Cwire Feedback Voltage Programming
2. 0
(Default)
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 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.
1. 5
1. 0
1
4
7
10
13
16
S2Cwire Data Register
Figure 8: AAT1231-1 SEL Pin Scaling Factor:
ILED (SEL = High) Divided by ILED (SEL = Low).
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
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.
1231.2008.06.1.5
www.analogictech.com
15
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
SEL = Low
SEL = High
Rising Clock
Edges/Data
Register
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1Ω
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1Ω
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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
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
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
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
Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1Ω
(Assume Nominal Values).
SEL = Low
SEL = High
Rising Clock
Edges/Data
Register
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1Ω
Reference
Voltage (V)
LED Current (mA);
RBALLAST = 30.1Ω
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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
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
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
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
Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1Ω
(Assumes Nominal Values).
16
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
Step-Up DC/DC Converters for White LED Backlight Applications
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 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
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 =
IAVG(OFF) =
IOUT
1 - DMAX
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.
10000
B340LA
MBR0530T
1000
ZHCS350
100
BAT42W
10
0.00
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.
Duty cycle is defined as the ON time divided by the total
switching interval.
D=
VOUT - VIN(MIN)
VOUT
The average diode current during the OFF time can be
estimated.
Forward Current (mA)
SwitchRegTM
0.10
0.20
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
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
TON
TON + TOFF
PLOSS(DIODE) = IAVG(TOT) · VF
= IOUT · VF
= TON ⋅ FS
For continuous LED currents, the diode junction temperature can be estimated.
TJ(DIODE) = TAMB + θJA · PLOSS(DIODE)
1231.2008.06.1.5
www.analogictech.com
17
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Manufacturer
Part Number
Rated
Forward
Current (A)
Diodes, Inc.
Diodes, Inc.
ON Semi
Zetex
Central Semi
B340LA
BAT42W
MBR0530T
ZHCS350
CMDSH2-3
3
0.2
0.5
0.35
0.2
Non-Repetitive
Peak Surge
Current (A)
Rated
Voltage (V)
Thermal
Resistance
(θJA, °C/W)
Case
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.
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.
Switching Frequency (MHz)
Selecting the Boost Inductor
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.
2.0
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
VIN = 2.7V
VOUT = 15V
50
60
70
80
90
100
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
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.
18
VIN = 3.0V
VOUT = 18V
1.8
40
Switching Frequency (MHz)
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.
www.analogictech.com
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)
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
Step-Up DC/DC Converters for White LED Backlight Applications
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.
IRMS =
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.
ing applied to the LIN node (non-switching) 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 (wound and gapped) inductors. In general, chip-type inductors have increased
winding resistance (DCR) when compared to shielded,
wound varieties.
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
Efficiency (%)
SwitchRegTM
77
Cooper SD3814-2R2 (77mΩ)
Cooper SD3110-2R2 (161mΩ)
74
71
68
65
2
5
8
11
14
17
20
LED Current (mA)
PLOSS(INDUCTOR) = IRMS2 · DCR
To ensure high reliability, the inductor case temperature
should not exceed 100ºC. In some cases, PCB heatsink-
Manufacturer
Sumida
www.sumida.com
Cooper Electronics
www.cooperet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
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
(mΩ)
Size (mm)
LxWxH
Type
CDRH2D11-2R2
2.2
780
78
3.2x3.2x1.2
Shielded
SD3814-2R2
SD3110-2R2
LQH3NPN2R2NG0
LQM2HPN2R2MG0
NR3010T-2R2M
2.2
2.2
2.2
2.2
2.2
1900
910
1250
1300
1100
77
161
164
80
95
4.0x4.0x1.4
3.1x3.1x1.0
3.0x3.0x1.0
2.5x2.0x1.0
3.0x3.0x1.0
CBC2016T2R2M
2.2
750
200
2.0x1.6x1.6
CBC2518T2R2M
2.2
510
90
2.5x1.8x1.8
Shielded
Shielded
Chip Coil Shield
Chip Coil Shield
Shielded
Chip
Non-Shielded
Shielded
Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT).
1231.2008.06.1.5
www.analogictech.com
19
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Selecting the Boost Capacitors
The high output ripple inherent in the boost converter
necessitates low impedance output filtering.
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.
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.
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 =
IOUT · DMAX
FS · ΔVOUT
To maintain stable operation at full load, the output
capacitor should be sized to maintain ΔVOUT between
100mV and 200mV.
20
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.
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:
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.
5. To avoid problems at startup, add a 10kΩ resistor
between the VIN, VP and EN/SET pins (R4). This is
critical in applications requiring immunity from input
noise during “hot plug” events, e.g. when plugged
into an active USB port.
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Manufacturer
Part Number
Value (μF)
Voltage Rating
Temp Co
Case Size
Murata
Murata
Murata
Murata
Murata
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.
AAT1231/1231-1
White LED
Driver
S2Cwire
Microcontroller
Figure 11: AAT1231/1231-1 Evaluation
Board Top Side Layout (with six LEDs
and microcontroller).
1231.2008.06.1.5
Figure 12: AAT1231/1231-1 Evaluation
Board Bottom Side Layout (with six LEDs
and microcontroller).
www.analogictech.com
21
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
VCC
R7
1K
R8
330
R6
1K
R5
1K
D7
RED
02
4
Down
Select
02
4
C3
1μF
U2
1
02
4
Up
SW3
2
1
3
5
3
4
SW2
1
3
5
S2Cwire
Microcontroller
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
8
7
6
R9
330
5
PIC12F675
D8
GREEN
(Select indicator)
SW1
1
3
5
R4
10K
J2
DC-
J3
DC+
DS1
Schottky
L1
J1
1
2
3
2.2μH
U1
VCC
1
2
JP1
3
4
C1
2.2μF
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
R2
226K
12
11
10
R3
12K
9
8
AAT1231/1231-1
White LED
Driver
VOUT
7
AAT1231/1231-1
R1
D6
D5
30.1Ω
LED
LED
D1
LED
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).
22
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Additional Applications
Efficiency vs. LED Current
L = 2.2μH
C1
2.2μF
LIN
VIN
SW
R2
187kΩ
C2
2.2μF
OVP
R3
12kΩ
ENSET
SEL
85
VIN = 5V
84
AAT1231/
1231-1
PGND
DS1
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
PVIN
(4 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 24V/
50mA max
83
82
81
80
VIN = 4.2V
VIN = 3.6V
79
78
FB
AGND
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
L = 2.2μH
C1
2.2μF
LIN
VIN
SW
83
82
AAT1231/
1231-1
PGND
R2
196kΩ
OVP
R3
12kΩ
ENSET
SEL
(5 White LEDs; RBALLAST = 30.1Ω
Ω)
FB
C2
2.2μF
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
PVIN
DS1
Up to 24V/
50mA max
VIN = 5V
81
80
VIN = 4.2V
79
VIN = 3.6V
78
77
76
AGND
30.1Ω
20mA
75
2
4
6
8
10
12
14
16
LED Current (mA)
Figure 15: Five LEDs In Series Configuration.
1231.2008.06.1.5
www.analogictech.com
23
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Efficiency vs. LED Current
(6 White LEDs; RBALLAST = 30.1Ω
Ω)
L = 2.2μH
C1
2.2μF
LIN
VIN
SW
Up to 24V/
50mA max
81
80
AAT1231/
1231-1
R2
226kΩ
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
PVIN
DS1
C2
2.2μF
OVP
PGND
R3
12kΩ
EN/SET
SEL
FB
AGND
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
18
20
LED Current (mA)
Figure 16: Six LEDs In Series Configuration.
Efficiency vs. LED Current
L = 2.2μH
PVIN
LIN
VIN
SW
84
83
AAT1231/
1231-1
PGND
(12 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 24V/
50mA max
R2
226kΩ
C2
2.2μF
OVP
R3
12kΩ
EN/SET
SEL
AGND
FB
30.1Ω
VIN = 5V
82
Efficiency (%)
Li-Ion
VIN = 2.7V
to 5.5V
C1
2.2μF
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
LED Current (mA)
Figure 17: Twelve LEDs In Series/Parallel Configuration.
24
www.analogictech.com
1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Multi-String White LED Configurations
for Digital Photo Frame Applications
(3S7P: 3 in series per string with 7 strings in parallel) is
shown in Figure 18. A scalable schematic and PCB layout
are illustrated in Figures 19 through 21.
The AAT1231 and AAT1231-1 can be configured to light
up as many as thirty-two white LEDs (WLED). This solution is scalable, flexible and good for digital photo frame
applications with multi-strings of WLEDs.
Efficiency vs. Total LED Current
(21 White LEDs [3 in Series, 7 in Parallel]; RBALLAST = 4.32Ω)
90
The multi-string WLED configuration can be composed of
many different parallel/series combinations, such as
6S2P, 6S3P, 5S4P, 5S5P, 5S6P, 4S7P, 4S8P, 3S9P, and
3S10P. ‘S’ is defined as the number of WLEDs in a series
per string. ‘P’ is defined as the number of strings of
WLEDs that are connected from the output voltage (VOUT)
to the ballast resistor, or in parallel. To match the
“brightness” of each separate string of WLEDs, each
string must have the same number of WLEDs in them.
The over-voltage protection (OVP) should also be adjusted according to the maximum feedback voltage plus the
maximum forward voltage (VF) of each WLED multiplied
by the total number of WLEDs in any of the parallel
strings of WLEDs. The efficiency of one configuration
VIN = 5V
VIN = 4.2V
VIN = 3.6V
Efficiency (%)
85
80
75
70
65
20
40
60
80
100
140
160
Total LED Current (mA)
Figure 18: Efficiency of the 3S7P
Multi-String Configuration.
VCC
R8
1k
R6
1k
D12
RED
R5
1k
R4
1k
1
2
3
4
SW3
Up
SW2
Down
U2
VDD
VSS
GP5
GP0
GP4
GP1
GP3
GP2
PIC12F675
C3
1µF
8
7
6
5
R7
1k
D11
GREEN
(Select
indicator)
SW1
Select
R9
10k
DC-
DC+
J2
VOUT
DS1
D Schottky
J3
L1
J1
VCC
JP1
1
2
3
C1
2.2µF
1
2
3
4
5
6
U1
VIN
EN
SEL
VP
N/C
SW
2.2µH
LIN
OVP
FB
GND
PGND
SW
JP2
R2
220K C2
2.2µF
R3
121K
12
11
10
9
8
7
AAT1231 TSOPJW-12
R1
D1a
LED
D2a
LED
D3a
LED
D1b
LED
D2b
LED
D3b
LED
D4a
LED
D5a
LED
D6a
LED
D1c
LED
D2c
LED
D3c
LED
D4b
LED
D5b
LED
D6b
LED
D7a
LED
D8a
LED
D1d
LED
D2d
LED
D3d
LED
D4c
LED
D5c
LED
D6c
LED
D7b
LED
D8b
LED
D9a
LED
D10a
LED
D1e
LED
D2e
LED
D3e
LED
D4d
LED
D5d
LED
D6d
LED
D7c
LED
D8c
LED
D9b
LED
D10b
LED
D1f
LED
D2f
LED
D3f
LED
D4e
LED
D5e
LED
D6e
LED
D7d
LED
D8d
LED
D9c
LED
D10c
LED
C1 10V 0603 X5R 2.2µF GRM188R60J225KE01
C2 25V 0805 X7R 2.2µF GRM21BR71E225KA73
DS1 B340LA
L1 2.2µH SD10-2R2, SD12-2R2, SD18-2R2
D1a-D10c White LED
Figure 19: Multi-String WLED Application Schematic.
1231.2008.06.1.5
www.analogictech.com
25
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Figure 20: Top Layer of the
Multi-String WLED Application.
Figure 21: Bottom Layer of the
Multi-String WLED Application.
The ballast resistor R1 is calculated based on the total
number of WLED strings and the total WLED current
required from the AAT1231 or AAT1231-1. The value
of the ballast resistor for each application is listed in
Table 7.
Number of
Parallel Strings
Total LED
Current (A)
R1 (Ω)
1% Tolerance
10
9
8
7
6
5
4
3
2
1
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
3.01
3.32
3.74
4.32
4.99
6.04
7.50
10.0
15.0
30.1
Table 7: Ballast Resistor Values for
Multi-String WLED Applications.
26
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1231.2008.06.1.5
PRODUCT DATASHEET
AAT1231
SwitchRegTM
Step-Up DC/DC Converters for White LED Backlight Applications
Ordering Information
Package
LED Current Control
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
TSOPJW-12
Increasing
Decreasing
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/about/quality.aspx.
Package Information
TSOPJW-12
2.85 ± 0.20
2.40 ± 0.10
0.20 + 0.10
- 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.
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3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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