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Número de pieza PT4110
Descripción High Efficiency White LED Driver
Fabricantes Powtech 
Logotipo Powtech Logotipo



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PT4110
High Efficiency White LED Driver
GENERAL DESCRIPTION
The PT4110 is a high efficiency step-up DC/DC
converter designed for driving multiple strings of up to
eight series-connected white LED from a single cell
Lithium Ion battery. It regulates the output current,
ideal for driving light emitting diodes (LED) whose
light intensity is proportional to the current passing
through them. The external ballast resistor sets the LED
current ranging from 5mA to 20mA, which can be
easily adjusted using either a DC voltage or a pulse
width modulated (PWM) signal alternatively. Its low
300mV feedback voltage reduces power loss and
improves efficiency.
The PT4110 has multiple features to protect itself from
fault conditions including built-in open load protection,
cycle-by-cycle current limit, over temperature
shutdown, input under voltage control and integrated
soft-start.
The PT4110 is available in SOT-89-5 and SOP-8
packages.
FEATURES
z 2.7V to 5.5V Input Voltage Range
z 35V Maximum Step-Up Voltage
z <1µA Shutdown Mode
z 1.2MHz Fixed Frequency Operation
z Cycle-By-Cycle Current Limit
z Open Load Protection
z Under Voltage Lockout
z Integrated Soft-Start
z Thermal Shutdown
z Frequency Jittering for better EMI performance
z SOT89-5 or SOP8 package
APPLICATIONS
z White LED Power Suppliers
z Flat Screen LCD Bias Suppliers
z Portable Media Players
z GPSs
z General middle-sized LCD backlight
ORDERING INFORMATION
PACKAGE
TEMPERATURE ORDERING PART
RANGE
NUMBER
SOT89-5, Pb free
-40to 85
PT4110E89E
SOP8, Pb free
-40to 85
PT4110ESOP
Note:
xxxxxX
Assembly Factory Code
Lot Number
TRANSPORT
MEDIA
Tape and Reel
Tape and Reel
MARKING
PT4110
xxxxxX
PT4110
xxxxxX
TYPICAL APPLICATION CIRCUIT
China Resources Powtech (Shanghai) Limited
PT4110_DS Rev EN_1.3
WWW.CRPOWTECH.COM
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PT4110 pdf
PT4110
High Efficiency White LED Driver
APPLICATION INFORMATION
Setting the LED current
The LED current is controlled by the feedback resistor.
The feedback reference is 300mV. The LED current is
300mV/RFB. In order to have accuracy LED current,
precision resistor is preferred. (1% is recommended).
Selecting the inductor
Choose an inductor that does not saturate under the
worst-case load transient and startup conditions. A good
rule for determining the inductance is to allow the
peak-to-peak ripple current to be approximately 30% to
50% of the maximum input current. Make sure that the
peak inductor current is below 1.2A to prevent loss of
regulation due to the current limit. For most of the
applications of the PT4110, it is recommended to use an
inductor of 10uH.
Selecting the Input Capacitor
An input capacitor is required to supply the AC ripple
current to the inductor, while limiting noise at the input
source. A low ESR capacitor is required to keep the
noise at the IC to a minimum. Ceramic capacitors are
preferred, but tantalum or low-ESR electrolytic
capacitors may also suffice.
Use an input capacitor value greater than 22μF. The
capacitor can be electrolytic, tantalum or ceramic.
However since it absorbs the input switching current it
requires an adequate ripple current rating. Use a
capacitor with RMS current rating greater than the
inductor ripple current.
open circuit. In some cases an LED may fail, which
will result in the feedback voltage always being zero.
The PT4110 will then switch at its maximum duty cycle
boosting the output voltage higher and higher. The
PT4110 detects the voltage of SW pin. The output of
PT4110 is equal high level of SW pin subtracting the
forward voltage of the Schottky diode. If the SW pin
exceeds 35V for several periods, the PT4110 will shut
down. The part will not switch again until the power is
recycled.
Dimming Control
There are two different types of dimming control
circuits:
1. Using a DC Voltage
For some applications, the preferred method of
brightness control is a variable DC voltage to adjust the
LED current. The dimming control using a DC voltage
is shown as below. As the DC voltage increases, the
voltage drop on R2 increases and the voltage drop on
R1 decreases. Thus, the LED current decreases. The
selection of R2 and R3 will make the current from the
variable DC source much smaller than the LED current
and much larger than the FB pin bias current.
Selecting the Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Low ESR capacitors are preferred to
keep the output voltage ripple to a minimum. The
characteristic of the output capacitor also affects the
stability of the regulation control system. 2.2uF ceramic,
tantalum, or low ESR electrolytic capacitors are
recommended.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To reduce
losses due to diode forward voltage and recovery time,
use a Schottky diode. Choose a diode whose maximum
reverse voltage rating is greater than the maximum
output voltage. The rated average forward current needs
to be equal to or greater than the load current.
Open Circuit Protection
when the input voltage exceeds 4.5V, the open load
protection will shut off the PT4110 if the output is in
2. Using a PWM Signal to EN Pin
With the PWM signal applied to the EN pin, the
reference of PT4110 is changed with the duty cycle of
the PWM signal. The LEDs operate at either zero or
full current. The average LED current increases
proportionally with the duty cycle of the PWM signal.
A 0% duty cycle will turn off the PT4110 and
corresponds to zero LED current. A 100% duty cycle
corresponds to full current. The typical frequency range
of the PWM signal should be higher than 20 kHz to
avoid the audio noise.
China Resources Powtech (Shanghai) Limited
PT4110_DS Rev EN_1.3
WWW.CRPOWTECH.COM
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