MAX1582ETC-T Maxim Integrated Products, MAX1582ETC-T Datasheet - Page 7

• Manufacturer Part Number: MAX1582ETC-T
• Description: LED Drivers High Efficiency 26V Step-Up Converter fo
• Manufacturer: Maxim Integrated Products

Specifications of MAX1582ETC-T

• Number Of Segments: 6
• Operating Supply Voltage: 2.6 V to 5.5 V
• Maximum Power Dissipation: 1349 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TQFN EP
• Minimum Operating Temperature: - 40 C

path between the input and the LEDs through the
inductor and Schottky diode. To ensure the LEDs
remain off when the MAX1582/MAX1582Y are in shut-
down, the minimum input forward voltage of the LED
array must exceed the maximum input voltage.
Typically, the leakage current through the LEDs in shut-
down is less than 1µA.
The MAX1582/MAX1582Y attain soft-start by charging
C
rises above 1.25V, the internal MOSFET begins switch-
ing, but at a reduced duty cycle. When V
above 2.25V, the duty cycle is at its maximum.
OVLO occurs when V
MAX1582Y). The protection circuitry stops the internal
MOSFET from switching and causes V
GND. The device comes out of OVLO and into soft-start
when V
Adjusting the MAX1582/MAX1582Ys’ output current
changes the brightness of the LEDs. The LED current is
set by the voltage at CTRL (V
resistor value (R
The V
0 to +1.62V. To set the maximum current, calculate
R
Power dissipation in R
therefore, a standard chip resistor is sufficient.
CTRL is also used as a digital input, allowing LED
brightness control with a logic-level PWM signal
applied directly to CTRL. The frequency range is from
200Hz to 200kHz, while 0% duty cycle corresponds to
zero current and 100% duty cycle corresponds to full
current. The error amplifier and compensation capaci-
tor form a lowpass filter, so PWM dimming results in DC
current to the LEDs without any additional RC filters
required.
SENSE
COMP
for White LED Main and Subdisplay Backlighting
CTRL
OUT1
gradually with a current source. When V
when V
voltage range for adjusting output current is
falls below 25V (16.7V for the MAX1582Y).
R
SENSE
CTRL
SENSE
I
LED
_______________________________________________________________________________________
is at its maximum as follows:
OUT1
):
=
SENSE
=
10
Overvoltage Protection
10
Adjusting LED Current
PWM Dimming Control
rises above 27V (18V for the
Design Procedure
×
V
is typically less than 5mW;
×
CTRL
R
1 62
I
LED MAX
SENSE
CTRL
.
High-Efficiency Step-Up Converters
(
) and the sense-
COMP
)
Soft-Start
COMP
to decay to
COMP
rises
The exact values of input and output capacitors are not
critical. The typical value for the input capacitor is
2.2µF, and the typical value for the output capacitor is
0.1µF. Larger value capacitors can be used to reduce
input and output ripple, but at the expense of size and
higher cost.
C
Connect a 0.022µF capacitor from COMP to GND. The
minimum value for C
time is found from:
Recommended inductor values range from 10µH to
47µH. A 22µH inductor optimizes the efficiency for most
applications, while maintaining a low 15mV
ple. With input voltages near 5V, a larger value of induc-
tance may be more efficient. To prevent core saturation,
ensure that the inductor saturation current rating exceeds
the peak inductor current for the application. Calculate
the peak inductor current with the following formula:
The MAX1582/MAX1582Ys’ high switching frequency
demands a high-speed rectification diode (D1) for opti-
mum efficiency. A Schottky diode is recommended due
to its fast recovery time and low forward-voltage drop.
Ensure that the diode’s average and peak current
rating exceeds the average output current and peak
inductor current. In addition, the diode’s reverse break-
down voltage must exceed V
current can be calculated from:
Due to fast-switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1582EVKIT) is available to speed design.
I
PEAK
COMP
≅
stabilizes the converter and controls soft-start.
V
OUT MAX
I
DIODE RMS
1
0 8
t
SS
(
Applications Information
.
×
(
=
)
V
COMP
C
×
IN MIN
Schottky Diode Selection
)
COMP
(
I
LED MAX
≅
is C
)
(
Capacitor Selection
I
×
OUT
Inductor Selection
OUT1
OUT
⎛
⎜
⎝
)
1 25
PC Board Layout
1
5
.
+
μ
×
/ 10. The soft-start
. The RMS diode
A
V
V
IN MIN
I
PEAK
⎞
⎟
⎠
(
P-P
2
)
×
input rip-
×
L
0 8
.
μ
s
7