Analogic AAT1239ITP-1-T1 40v step-up converter for 4 to 10 white led Datasheet

PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
General Description
Features
The AAT1239-1 is a high frequency, high efficiency constant current boost converter capable of driving up to
ten (10) series-connected white LEDs or 40V. It is an
ideal power solutions for backlight applications with up
to ten white LEDs in series. The input voltage is 2.7V to
5.5V for single-cell lithium-ion/polymer (Li-ion) based
portable devices.
• Input Voltage Range: 2.7V to 5.5V
• Maximum Continuous Output 40V @ 30mA
• Drives up to 10 LEDs in Series
▪ Constant LED Current with 3.5% Accuracy Over
Temperature and Input Voltage Range
• 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
AAT1239 operation, LED brightness increases based on
the data applied at the EN/SET pin. The SEL logic pin
changes the feedback voltage between two programmable ranges.
The AAT1239-1 features a 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 AAT1239-1
offers 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.
Applications
The AAT1239-1 is available in the Pb-free, thermallyenhanced 12-pin TSOPJW package.
•
•
•
•
•
Color Display Backlight
Digital Still Cameras (DSCs)
Digital Photo Frames
PDAs and Notebook PCs
White LED Drivers
Typical Application
L1
2.2μH
LIN
PVIN
Li-Ion:
VIN = 2.7V to 4.2V
C1
2.2μF
DS1
SS16L or equivalent
VIN
C2
2.2μF
M673
SW
R2
374k
AAT1239-1
OVP
Enable/Set
Feedback Voltage
Select
EN/SET
R3
12k
SEL
FB
PGND
AGND
ILED
20mA
1239-1.2007.10.1.0
R1 (RBALLAST)
30.1
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White LEDs
OSRAM LW M678
or equivalent
1
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Pin Descriptions
Pin #
Symbol
1
2
PVIN
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. 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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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Part Number Descriptions
SEL Polarity
Part Number
AAT1239ITP-1
HIGH
0.6V ≥ VFB ≥ 0.3V
LOW
S2C Feedback Voltage Programming
0.4V ≥ VFB ≥ 0.1V
See Table 2
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
45
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.
1239-1.2007.10.1.0
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3
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
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
Description
Conditions
Input Voltage Range
Maximum Output Voltage
Operating Current
Shutdown Current
Maximum Continuous Output
Current2
Line Regulation
Low Side Switch On Resistance
Input Disconnect Switch
On Resistance
Typ
Max
Units
SEL = GND, FB = 0.1V
EN/SET = GND
5.5
40
70
1.0
V
V
μA
μA
2.7V < VIN < 5.5V, VOUT = 40V
30
mA
2.7
VIN = 2.7V to 5.5V, VFB = 0.6V
Soft-Start Time
Over-Voltage Protection Threshold
Over-Voltage Hysteresis
N-Channel Current Limit
TJ Thermal Shutdown Threshold
TJ Thermal Shutdown Hysteresis
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
Min
From Enable to Output Regulation;
VFB = 300mV
VOUT Rising
VOUT Falling
1.1
0.7
135
%
mΩ
180
mΩ
400
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
1.4
0.3
75
75
500
500
1
-1
AAT1239-1
VFB
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
0.085
0.1
1.115
0.54
0.6
0.66
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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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Typical Characteristics
Efficiency vs. LED Current
Efficiency vs. LED Current
(9 White LEDs; RBALLAST = 30.1Ω
Ω)
80
78
78
76
VIN = 5V
76
Efficiency (%)
Efficiency (%)
(10 White LEDs; RBALLAST = 30.1Ω
Ω)
74
72
70
66
VIN = 3.6V
VIN = 4.2V
68
2
4
6
8
10
VIN = 5V
74
72
VIN = 3.6V
VIN = 4.2V
70
68
12
14
16
18
66
20
2
4
6
8
10
ILED (mA)
Input Voltage (top) (V)
Output Voltage (middle) (V)
Shutdown Current (µA)
25°C
85°C
0.4
-40°C
0.0
3.5
3.9
4.3
4.7
5.1
4.2V
3.6V
33.2
33
32.8
0.62
0.6
0.58
5.5
Input Voltage (V)
Time (50µs/div)
Accuracy ILED vs. Input Voltage
Accuracy ILED vs. Temperature
(VFB = 0.6V; RBALLAST = 30.1Ω
Ω)
(VFB = 0.6V; RBALLAST = 30.1Ω
Ω)
1.5
2.0
-40°C
1.0
Accuracy ILED (%)
Accuracy ILED (%)
1.5
0.5
0.0
85°C
25°C
-0.5
-1.0
-1.5
-2.0
2.7
20
Feedback Voltage (bottom) (V)
0.8
3.1
18
Line Transient
1.0
2.7
16
(10 White LEDs; RBALLAST = 30.1Ω
Ω)
(EN = GND)
0.2
14
ILED (mA)
Shutdown Current vs. Input Voltage
0.6
12
3.2
3.7
4.2
4.7
5.2
5.7
1.0
0.5
0.0
-0.5
-1.0
-1.5
-40
Input Voltage (V)
1239-1.2007.10.1.0
-15
10
35
60
85
Temperature (°C)
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5
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Soft Start
(10 White LEDs; VFB = 0.3V)
0V
0.4
0.2
0
2
1
0
3.3V
0V
0V
0.4
0.2
2
0
1
0
Time (200µs/div)
Shutdown
(10 LEDs; VFB = 0.3V)
0V
0.6
0.4
0.2
0.5
0.0
3.3V
0V
0.4
0.2
0
0.5
0
Time (100µs/div)
Time (50µs/div)
Output Ripple
Output Ripple
(10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 13mA)
(10 White LEDs; VIN = 3.6V; COUT = 2.2µF; ILED = 20mA)
VOUT
(AC Coupled)
(20mV/div)
VOUT
(AC Coupled)
(20mV/div)
VSW
(20V/div)
VSW
(20V/div)
IL
(500mA/div)
IL
(500mA/div)
Time (200ns/div)
6
Inductor Current (bottom) (A)
3.3V
EnableVoltage (top) (V)
Feedback Voltage (middle) (V)
Shutdown
(10 White LEDs; VFB = 0.6V)
Inductor Current (bottom) (A)
EnableVoltage (top) (V)
Feedback Voltage (middle) (V)
Time (200µs/div)
0
EnableVoltage (top) (V)
Inductor Current (bottom) (A)
3.3V
0.6
Feedback Voltage (middle) (V)
Soft Start
(10 White LEDs; VFB = 0.6V)
EnableVoltage (top) (V)
Inductor Current (bottom) (A)
Feedback Voltage (middle) (V)
Typical Characteristics
Time (200ns/div)
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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Transition of LED Current
(10 White LEDs; SEL = Low; ILED = 13mA to 6mA)
34
30
28
0.4
0.3
0.2
0.1
34
32
30
0.4
0.3
0.2
0.1
0.0
0.0
Time (50µs/div)
Time (50µs/div)
Low Side Switch On Resistance
vs. Input Voltage
300
260
280
240
100°C
240
220
200
180
85°C
25°C
200
100°C
180
160
85°C
140
120
160
140
2.7
120°C
220
120°C
RDS(ON)L (mΩ
Ω)
RDS(ON)IN (mΩ
Ω)
Input Disconnect Switch Resistance
vs. Input Voltage
260
100
3.1
3.5
3.9
4.3
4.7
5.1
25°C
80
2.7
5.5
3.1
3.5
Input Voltage (V)
4.3
4.7
5.1
5.5
EN/SET Off Timeout vs. Input Voltage
300
350
EN/SET Off Timeout (µs)
EN/SET Latch Timeout (µs)
3.9
Input Voltage (V)
EN/SET Latch Timeout vs. Input Voltage
300
-40°C
250
85°C
200
25°C
150
100
2.7
Feedback Voltage
(bottom) (V)
32
Output Voltage (top) (V)
Transition of LED Current
(10 White LEDs; SEL = Low; ILED = 3mA to 13mA)
Feedback Voltage
(bottom) (V)
Output Voltage (top) (V)
Typical Characteristics
3.1
3.5
3.9
4.3
4.7
5.1
5.5
200
25°C
150
85°C
100
50
2.7
Input Voltage (V)
1239-1.2007.10.1.0
-40°C
250
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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7
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Enable High Threshold (VIH) vs. Input Voltage
Enable Low Threshold (VIL) vs. Input Voltage
Enable High Threshold (VIH) (V)
Enable Low Threshold (VIL) (V)
Typical Characteristics
1.2
1.1
1.0
25°C
-40°C
0.9
85°C
0.8
0.7
0.6
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
1.2
1.1
1.0
0.9
25°C
0.8
0.7
85°C
0.6
0.5
0.4
Input Voltage (V)
8
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Functional Block Diagram
LIN
PVIN
VIN
OVP
EN/SET
SW
Control
FB
Reference
Output
Select
SEL
AGND
Functional Description
The AAT1239-1 consists 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
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
the level of the feedback reference voltage which is programmed through the S2Cwire interface. The SEL pin
selects one of two feedback voltage ranges. In the
AAT1239-1, the SEL function is inverted in that the FB
pin voltage can be programmed from 0.4V to 0.1V with
1239-1.2007.10.1.0
PGND
a logic LOW applied to the SEL pin and 0.6V to 0.3V with
a logic HIGH applied to the SEL pin. 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 some applications requiring a short duration of
boosting current applying a low-to-high transition on the
AAT1239-1’s SEL pin, LED current can be programmed
up to 3x. The step size is determined by the programmed
voltage at the FB pin where the internal default setting
is 1.5x in the AAT1239-1.
Control Loop
The AAT1239-1 provides 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 AAT1239-1 modulates the power MOSFET switching
current to maintain the programmed FB voltage. This
allows the FB voltage loop to directly program the
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9
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
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 AAT1239-1
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).
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 AAT1239-1 provides 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 40V.
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
10
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 AAT1239-1 has 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 decreased (as in the AAT1239-1; see Table 2) 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.
Thermal protection disables the AAT1239-1 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.
Over-Voltage Protection
Over-voltage protection prevents damage to the
AAT1239-1 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 overvoltage 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.
Under-Voltage Lockout
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.
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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Application Information
Assume R3 = 12kΩ and VOUT(MAX) = 40V. Selecting 1%
resistor for high accuracy, this results in R2 = 374kΩ
(rounded to the nearest standard value). The minimum
OVP threshold can be calculated:
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 40V
(VOUT(MAX)). The value of R3 should be selected from 10kΩ
to 20kΩ to minimize losses without degrading noise
immunity.
R2 = R3 ·
VOUT(OVP_MIN) = VOVP(MIN) ·
= 35.4V
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) ⎞
-1
⎝ VOVP
⎠
VOUT(MAX) < VOUT(OVP_MIN)
In some cases, this may disallow configurations with
high LED forward voltage (VFLED) and/or greater than ten
series white LEDs. VFLED unit-to-unit tolerance can be as
high as +15% of nominal for white LED devices.
VOUT
AAT1239-1
OVP Constant Voltage Operation
R2
COUT
OVP
R3
GND
⎛ R2
⎞
+1
⎝ R3
⎠
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
1.238V
1.142V
40
30
4
2
0
Time (4ms/div)
Figure 2: Over-Voltage Protection
Open Circuit Response (No LED).
1239-1.2007.10.1.0
Output Voltage (middle) (V)
Over Voltage Protection Pin (top) (V)
Inductor Current (bottom)(A)
Figure 1: Over-Voltage Protection Circuit.
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 ten series white
LED string and VOVP = 40V. 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.
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PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Over-Voltage Protection
Cold Temperature Apply
Self-Recovery
where:
VFB(MAX) = 0.4V when SEL = Low
VOUT
(5V/div)
VFB(MAX) = 0.6V when SEL = High
i.e., for a maximum LED current of 20mA (SEL = High):
ILED
(200mA/div)
RBALLAST =
Figure 3: Over-Voltage Protection
Constant Voltage Operation
(10 White LEDs; ILED = 20mA;
R2 = 12kΩ; R3 = 374kΩ).
Maximum ILED
Current (mA)
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 45V under worstcase operating conditions.
VSW(MAX) = VOVP(MAX) ·
VOUT(OVP_MIN) = VOVP(TYP) ·
N=
The AAT1239-1 is well suited for driving white LEDs with
constant current. Applications include main and sub-LCD
display backlighting, and color LEDs.
(VOUT(OVP_MIN) - VFB(MAX))
VFLED(MAX)
VOUT(OVP_MIN) = 1.2V ·
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:
12
⎛ R2
⎞
+1
⎝ R3
⎠
Figure 4 shows the schematic of using ten LEDs in series.
Assume VFLED @ 20mA = 3.5V (typical) from LW M673
(OSRAM) datasheet.
LED Selection and Current Setting
VFB(MAX)
ILED(MAX)
13.3
16.2
20.0
26.7
40.2
80.6
Typical white LEDs are driven at maximum continuous
currents of 15mA to 20mA. The maximum number 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.
VF = -Schottky Diode DS1 forward voltage at turn-OFF
RBALLAST =
SEL = Low
20.0
24.3
30.1
40.2
60.4
121.0
Table 1: Maximum LED Current and RBALLAST
Resistor Values (1% Resistor Tolerance).
⎛ R3
⎞
+ 1 + VF + VRING
⎝ R2
⎠
VRING = Voltage ring occurring at turn-OFF
RBALLAST (Ω)
SEL = High
30
25
20
15
10
5
While OVP is active, the maximum LED current programming error (ΔILED) is proportional to voltage error across
an individual LED (ΔVFLED).
(N · VFLED(TYP) - VOUT(OVP_MIN) - VFB)
ΔVFLED =
N
VFB
0.6
=
= 30Ω ≈ 30.1Ω
ILED(MAX)
0.020
N=
⎛ 374kΩ
⎞
+ 1 = 38.6V
⎝ 10.4kΩ
⎠
38.6V - 0.6V
3.5V
≈ 10.9
Therefore, under these typical operating conditions, ten
LEDs can be used in series.
www.analogictech.com
1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
DS1
L1
2.2μH
D1
LED
VCC
D6
LED
JP1
C1
2.2μF
R4 10K
1
2
3
Enable
JP2
U1
1
2
3
4
5
6
VIN
EN
SEL
VP
N/C
SW
LIN
OVP
FB
GND
PGND
SW
R2
374K
12
11
10
9
8
7
D7
LED
D3
LED
D8
LED
R3
12K
D4
LED
D9
LED
AAT1239-1 TSOP12JW
1
2
3
D2
LED
D5
LED
D10
LED
R1
Select
C2
2.2μF
30.1
C1 10V 0603 X5R 2.2μF GRM188R60J225KE01D
C2 50V 1206 X7R 2.2μF GRM31CR71H225KA88
L1 2.2μH SD3814-2R2 or SD3110-2R2
DS1 SS16L
D1-D10 LW M673 White LED
other alternatives:
more stability at 40V: C2 50V 1206 X7R 4.7μF GRM31CR71H475K
under 20V application: C2 25V 0805 X7R 2.2μF GRM21BR71E225KA73L
Figure 4: AAT1239-1 White LED Boost Converter Schematic.
LED Brightness Control
LED Current (mA)
25
The AAT1239-1 uses 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 AAT1239-1 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.
20
SEL=HIGH
Default
15
10
SEL=LOW
5
0
1
4
7
10
13
16
S2Cwire Data Register
Figure 5: Programming AAT1239-1 LED Current
with RBALLAST = 30.1Ω.
1239-1.2007.10.1.0
www.analogictech.com
13
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Alternatively, toggling the SEL logic pin from low to high
implements stepped or pulsed LED currents by increasing the FB pin voltage. Figure 6 illustrates the SELECT
pin scaling factor, defined as the LED current with
SEL=HIGH divided by the LED current with SEL=LOW. In
the AAT1239-1, the possible scaling factors are 3.0x to
1.5x with the internal default setting of 1.5x.
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
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
AAT1239-1 is disabled. When the AAT1239-1 is disabled,
the register is reset to its default value. In the AAT1239-1,
the FB pin voltage is set to 0.3V if the EN/SET pin is
subsequently pulled HIGH.
Select Pin Scaling Factor
(Low to High)
3. 5
3. 0
2. 5
2. 0
(Default)
1. 5
1. 0
1
4
7
10
13
16
S2Cwire Feedback Voltage Programming
S2Cwire Data Register
The FB pin voltage is set to the default level at initial
powerup. The AAT1239-1 is programmed through the
S2Cwire interface. Table 2 illustrates FB pin voltage programming for the AAT1239-1. 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 of the AAT1239-1,
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.
Figure 6: AAT1239-1 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
THI
TLO
TOFF
T LAT
EN/SET
1
Data Reg
2
n-1
n ≤ 16
0
n-1
0
Figure 7: AAT1239-1 S2Cwire Timing Diagram to Program the Output Voltage.
14
www.analogictech.com
1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
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 2: AAT1239-1 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 AAT1239-1 boost converter. 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 nonrepetitive 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.
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.
Duty cycle is defined as the ON time divided by the total
switching interval.
40V rated Schottky diodes are recommended for outputs
less than 30V, while 60V rated Schottky diodes are recommended for outputs greater than 35V.
D=
TON
TON + TOFF
= TON ⋅ FS
*All table entries are preliminary and subject to change without notice.
1239-1.2007.10.1.0
www.analogictech.com
15
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
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 =
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.
Selecting the Boost Inductor
VOUT - VIN(MIN)
VOUT
The AAT1239-1 controller utilizes 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.
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.
A better estimate of DMAX is possible once VF is known.
PLOSS(DIODE) = IAVG(TOT) · VF
= IOUT · VF
DMAX =
For continuous LED currents, the diode junction temperature can be estimated.
Where VF is the Schottky diode forward voltage. If not
known, it can be estimated at 0.5V.
TJ(DIODE) = TAMB + θJA · PLOSS(DIODE)
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.
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.
Manufacturer
Part Number
Taiwan Semiconductor
Co., Ltd.
SS16L
SS15L
SS14L
Diodes, Inc
B340LA
Zetex
ZHCS350
Rated
Forward
Current
(A)
(VOUT + VF - VIN(MIN))
(VOUT + VF)
Non-Repetitive
Peak Surge
Current (A)
Rated
Voltage
(V)
Thermal
Resistance
(θJA, °C/W)
Size (mm)
(LxWxH)
Case
1.1
30
30
30
60
50
40
45
45
45
3.8x1.9x1.43
3.8x1.9x1.43
3.8x1.9x1.43
Sub SMA
Sub SMA
Sub SMA
3
70.0
40
25
5.59x2.92x2.30
SMA
0.35
4.2
40
330
1.7x0.9x0.8
SOD523
Table 3: Typical Surface Mount Schottky Rectifiers for Various Output Levels.
16
www.analogictech.com
1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
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.
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.
IRMS =
Sumida
www.sumida.com
Cooper Electronics
www.cooperet.com
Taiyo Yuden
www.t-yuden.com
To ensure high reliability, the inductor case temperature
should not exceed 100ºC. In some cases, PCB heatsinking 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 AAT1239-1.
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 8
for ten white LEDs in series. Smaller inductors yield
increased DCR and reduced operating efficiency.
75
CDRH5D16F-2R2 (29mΩ)
72
SD3814-2R2 (77mΩ)
69
66
63
IPEAK
2
5
3
8
11
14
17
20
LED Current (mA)
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.
Manufacturer
PLOSS(INDUCTOR) = IRMS2 · DCR
Efficiency (%)
SwitchRegTM
Figure 8: AAT1239-1 Efficiency for
Different Inductor Types (VIN = 3.6V;
Ten White LEDs in Series).
Part Number
Inductance
(μH)
Maximum DC ISAT
Current (mA)
DCR
(mΩ)
Size (mm)
LxWxH
Type
CDRH2D14-2R2
2.2
1500
75
3.2x3.2x1.55
Shielded
SD3814-2R2
SD3110-2R2
NP03SB-2R0M
NR3010T-2R2M
2.2
2.2
2
2.2
1900
910
1900
1100
77
161
32
95
4.0x4.0x1.0
3.1x3.1x1.0
4.0x4.0x1.8
3.0x3.0x1.0
Shielded
Shielded
Shielded
Shielded
Table 4: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT).
1239-1.2007.10.1.0
www.analogictech.com
17
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
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 AAT1239-1
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, 50V
rated capacitors are required for the 40V maximum
boost output. Ceramic capacitors sized as small as 0805
or 1206 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.
Manufacturer
Murata
Murata
Murata
Murata
Murata
Part Number
GRM188R60J225KE19
GRM188R61A225KE34
GRM21BR71E225KA73L
GRM31CR71H225KA88
GRM31CR71H475K
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 AAT1239-1
boost converter is shown in Figures 9 and 10. 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.
Value (μF)
Voltage Rating
Temp Co
Case Size
2.2
2.2
2.2
2.2
4.7
6.3
10
25
50
50
X5R
X5R
X7R
X7R
X7R
0603
0603
0805
1206
1206
Table 5: Recommended Ceramic Capacitors.
18
www.analogictech.com
1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Figure 9: AAT1239-1 Evaluation
Board Top Side Layout (with ten LEDs
and microcontroller).
Figure 10: AAT1239-1 Evaluation
Board Bottom Side Layout (with ten LEDs
and microcontroller).
S2Cwire
Microcontroller
VCC
R7
1k
R8
330Ω
R6
1k
R5
1k
1
2
S1
3
Select
D12
Red
4
S2
Down
C3
0.1μF
U2
PIC12F675
VDD
VSS
GP5
GP0
GP4
GP1
GP2
GP3
8
7
6
R9
330Ω
5
S3
D11
Green
Up
JP2
JP3
R4
10k
DC-
DC+
C
10μF
VCC
1 2 3
1
U1
AAT1239-1
VIN
EN
3
SEL
JP1
2
4
C1
2.2μF
5
6
VOUT
R2
374k
12
LIN
11
OVP
10
FB
GND
8
PGND
SW
SW
JP4
D1
WLED
R3
12k
9
VP
N/C
AAT1239-1
White LED
Driver
DS1
Schottky
L1
2.2μH
C2
2.2μF
D2
WLED
D3
WLED
7
D4
WLED
D5
WLED
R1
30.1Ω
D10
WLED
D9
WLED
D8
WLED
D6
D7
WLED WLED
Figure 11: AAT1239-1 Evaluation Board Schematic (with ten LEDs and microcontroller).
1239-1.2007.10.1.0
www.analogictech.com
19
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Additional Applications
Efficiency vs. LED Current
PVIN
Li-Ion
VIN = 2.7V
to 5.5V
C1
2.2μF
VIN
DS1
Schottky
SW
AAT1239-1
OVP
84
C2
2.2μF
R3
12k
D2
LED
D3
LED
D4
LED
PGND
EN/SET
SEL
FB
AGND
R1
30.1Ω
83
D1
LED
R2
158k
LIN
(4 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 17V/
30mA max
VIN = 5V
82
Efficiency (%)
L1
2.2μH
81
80
79
VIN = 3.6V
VIN = 4.2V
78
77
76
20mA
75
74
2
4
6
8
10
12
14
16
18
20
18
20
18
20
ILED (mA)
Figure 12: Four LEDs In Series Configuration.
Efficiency vs. LED Current
PVIN
Li-Ion
VIN = 2.7V
to 5.5V
C1
2.2μF
VIN
DS1
Schottky
SW
AAT1239-1
OVP
C2
2.2μF
R3
12k
SEL
D2
LED
D3
LED
D4
LED
PGND
EN/SET
80
D1
LED
R2
287k
LIN
(8 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 30V/
30mA max
D5
LED
FB
AGND
R1
30.1Ω
D8
LED
20mA
D7
LED
VIN = 5V
78
Efficiency (%)
L1
2.2μH
D6
LED
76
74
72
VIN = 3.6V
VIN = 4.2V
70
68
66
2
4
6
8
10
12
14
16
ILED (mA)
Figure 13: Eight LEDs In Series Configuration.
Efficiency vs. LED Current
PVIN
Li-Ion
VIN = 2.7V
to 5.5V
C1
2.2μF
VIN
DS1
Schottky
SW
AAT1239-1
OVP
C2
2.2μF
R3
12k
SEL
D2
LED
D3
LED
D4
LED
PGND
EN/SET
78
D1
LED
R2
324k
LIN
(9 White LEDs; RBALLAST = 30.1Ω
Ω)
Up to 34V/
30mA max
D5
LED
FB
AGND
R1
30.1Ω
20mA
D9
LED
D8
LED
D7
LED
D6
LED
VIN = 5V
76
Efficiency (%)
L1
2.2μH
74
72
VIN = 4.2V
70
VIN = 3.6V
68
66
2
4
6
8
10
12
14
16
ILED (mA)
Figure 14: Nine LEDs In Series Configuration.
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1239-1.2007.10.1.0
PRODUCT DATASHEET
AAT1239-1
SwitchRegTM
40V Step-Up Converter for 4 to 10 White LEDs
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
ZLXYY
AAT1239ITP-1-T1
Package Information
TSOPJW-12
2.40 ± 0.10
2.85 ± 0.20
0.20 + -0.10
0.05
0.50 BSC
0.50 BSC
0.50 BSC
0.50 BSC
0.50 BSC
7° NOM
0.055 ± 0.045
0.04 REF
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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Phone (408) 737-4600
Fax (408) 737-4611
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