Download AT6731

AT6731
White LED Step-Up Converter
Immense Advance Tech.
FEATURES
DESCRIPTION

Inherently Matched LED Current
The AT6731 is a step-up DC/DC converter

Drives Up to 27 LEDs From a 5V Supply
specifically designed to drive white LEDs with a

36V Rugged Bipolar Switch
constant current. The device can drive up to 27

Fast 1.2MHz Switching Frequency
LEDs from a 5V supply.

Over Voltage Protection
The AT6731 implements a 1.2MHz control scheme.
The high frequency operation saves board space by
reducing external component sizes.
To optimize efficiency, the feedback voltage is set to
APPLICATION
only 95mV. This reduces the power dissipation in

Cellular Phones

PDAs, Handheld Computers

Digital Cameras

Mp3 Players

GPS Receivers
the current set resistor and allows the lowest total
output voltage, hence minimal current draw from the
battery.
Additional feature include output voltage limiting
when LEDs are disconnected.
PIN CONFIGURATIONS (TOP VIEW)
ORDER INFORMATION
AT 6731-KF R
IAT
Circuit Type
Shipping:
R: Tape & Reel
KF: SOT-26
S8: SOP-8
Rev 1.1
1
AT6731
White LED Step-Up Converter
Immense Advance Tech.
PIN DESCRIPTIONS
Pin Name
SW
GND
FB
Pin Description
Switch Pin. (Minimize trace area at this pin to reduce EMI.)
Ground Pin. Connect directly to local ground plane.
Feedback Pin. Reference voltage is 95mV.
(Calculate resistor value according to the formula RFB = 95mV / ILED.)
EN
Enable Pin. (Connect to 1.5V or higher to enable device; 0.4V or less to disable device.)
VIN
Input Supply Pin. (Must be locally bypassed.)
Vout
Over Voltage Protection Pin. Voltage sensing input to trigger the function of over-voltage protection
TYPICAL APPLICATION CIRCUIS
Figure .1
Rev 1.1
2
AT6731
White LED Step-Up Converter
Immense Advance Tech.
BLOCK DIAGRAM
Figure .2
OPERATION
The AT6731 uses a constant frequency, current mode control scheme to provide excellent line and load
regulation. Operation can be best understood by referring to the block diagram in Figure 2. At the start of
each oscillator cycle, the RS latch is set, which turns on the power switch Q1. A voltage proportional to the
switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM
comparator A2. When this voltage exceeds the level at the negative input of A2, the RS latch is reset turning
off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an
amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this
manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error
amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered.
Rev 1.1
3
AT6731
White LED Step-Up Converter
Immense Advance Tech.
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter
Range
Unit
Input Voltage (VIN )
10
V
SW Voltage
36
V
FB Voltage
10
V
EN Voltage
10
V
-40 to +85
°C
125
°C
-65 to +150
°C
260
°C
Operating Temperature Range
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering, 5sec)
SOT-26
300
TA=25°C (Note 2)
SOP8
400
Thermal Resistance
SOT-26(Note 3)
333
Junction to Ambient
SOP8
160
Power Dissipation
Thermal Resistance
Junction to Case
PD @
SOT-26
106.6
mW
°C/W
C/W
Note 1: Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress
ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections
of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain
possibility to affect device reliability.
Note 2: Thermal Resistance is specified with the component mounted on a low effective thermal conductivity test board in free air at
TA=25°C.
Note 3: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
Rev 1.1
4
AT6731
White LED Step-Up Converter
Immense Advance Tech.
ELECTRICAL CHARACTERISTICS
TA= 25°C, VIN= 5V, VEN =5V, unless otherwise specified.
Parameter
Symbol
Minimum Operating Voltage
VIN_Min
Maximum Operating Voltage
VIN_Max
Feedback Voltage
IFB
FB Pin Bias Current
IFB_BIAS
Supply Current
ISUPPLY
Condition
Min
Typ
Max
2.5
Unit
V
10
V
ILOAD = 180mA, VIN = 5V
83
95
107
ILOAD= 100mA, VIN = 5V
86
95
104
10
45
100
nA
2.1
3.0
mA
0.1
1.0
μA
1.6
MHz
EN = 0V
mV
Switching Frequency
IFREQ
0.8
1.2
Maximum Duty Cycle
DCMAX
85
90
%
Switch Current Limit
ILIMIT
650
mA
ISW = 250mA
350
mV
VSW = 5V
0.01
Switch VCESAT
Switch Leakage Current
VCESAT
VSW_LEAKAGE
EN Voltage High
EN_H
EN Voltage Low
EN_L
EN Pin Bias Current
OVP Threshold
5
1.5
μA
V
0.4
V
IEN
65
μA
VOVP
29
V
Rev 1.1
5
AT6731
White LED Step-Up Converter
Immense Advance Tech.
TYPICAL OPERATING CHARACTERISTICS
Rev 1.1
6
AT6731
White LED Step-Up Converter
Immense Advance Tech.
APPLICATIONS INFORMATION
Inductor Selection
Schottky diodes with higher current ratings usually
A 10μH inductor is recommended for most AT6731
have lower forward voltage drop and larger diode
applications. Although small size and high efficiency
capacitance, which can cause significant switching
are major concerns, the inductor should have low
losses at the 1.2MHz switching frequency of the
core losses at 1.2MHz and low DCR (copper wire
AT6731. A Schottky diode rated at 1000mA it is
resistance).
sufficient for most AT6731 applications.
Recommended Inductors
Rated
Rated
Part No.
Size
DCR
(WxLxH:mm)
(Ω)
Dimming Control
There are two techniques for dimming control. One
Current,
Inductance
(μH)
Irms (A)
10
2.08
is PWM dimming, and the other is continuous
dimming.
7.6 x 7.6 x
DR73-100-R
0.0656
1. PWM dimming control is implemented by
3.55
applying a PWM signal on EN pin as shown in
5.2 x 5.2 x
SD14-100-R
10
1.1
0.1913
Figure 3. The AT6731 is turned on and off by the
1.45
PWM signal. With this method, the LEDs
4.0 x 4.5 x
LD1-100-R
10
1.13
0.1820
operate with either zero or full current. The
3.2
COOPER Bussmann
average LED current is increased proportionally
http://www.cooperbussmann.com
to the duty-cycle of the PWM signal. This
technique has high-efficiency because the IC
Capacitor Selection
and the LEDs consume no current during the off
The small size of ceramic capacitors makes them
cycle of the PWM signal. Typical PWM
ideal for AT6731 applications. X5R and X7R types
are
recommended
because
they
retain
frequency should be between 100Hz and
their
10KHz.
capacitance over wider voltage and temperature
2. Continuous dimming control is implemented by
ranges than other types such as Y5V or Z5U. A
applying a DC control voltage to the FB pin of
4.7μF input capacitor and a 4.7μF output capacitor
the AT6731 through a series resistor as shown
are sufficient for most AT6731 applications.
in Figure 4. The LED intensity (current) can by
dynamically varied applying a DC voltage to the
Diode Selection
FB pin. The DC voltage can come from a DAC
The Schottky diodes, with their low forward voltage
signal, or a filtered PWM signal. The advantage
drop and fast reverse recovery, are the ideal choices
of this approach is a high frequency PWM signal
for AT6731 applications. The forward voltage drop of
(>10KHz) that can be used to control LED
a Schottky diode represents the conduction losses
intensity.
in the diode, while the diode capacitance (CT or CD)
represents the switching losses. For diode selection,
both forward voltage drop and diode capacitance
need to be considered.
Rev 1.1
7
AT6731
White LED Step-Up Converter
Immense Advance Tech.
APPLICATION INFORMATION (CONTINUED)
Figure 3. PWM Dimming Method
Figure 4. Continuous Dimming
Rev 1.1
8
AT6731
White LED Step-Up Converter
Immense Advance Tech.
PACKAGE OUTLINE DIMENSIONS
Rev 1.1
9
AT6731
White LED Step-Up Converter
Immense Advance Tech.
Note :
Information provided by IAT is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry
other than circuitry entirely embodied in an IAT product; nor for any infringement of patents or other rights of third parties that may result
from its use. We reserve the right to change the circuitry and specifications without notice.
Life Support Policy: IAT does not authorize any IAT product for use in life support devices and/or systems. Life support devices or
systems are devices or systems which, (I) are intended for surgical implant into the body or (II) support or sustain life, and whose failure
to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a
significant injury to the user. Typical numbers are at 25°C and represent the most likely norm.
Rev 1.1
10