IS31LT3117 Datasheet, PDF (10/15 Pages) Integrated Silicon Solution, Inc – 53V, 350MA, 4-CHANNEL CONSTANT CURRENT REGULATOR WITH OTP

IS31LT3117
APPLICATION INFORMATION
FUNCTIONAL DESCRIPTION
IS31LT3117 is a linear current regulator designed to
drive high brightness LEDs. The device integrates 4
channels capable of driving up to 350mA in each
channel and operates over a supply voltage range of
6V to 53V. Output current is easily programmed by
using a single resistor.
The IS31LT3117 incorporates a special thermal
regulation protection feature which prevents the die
temperature from exceeding the maximum rated
junction temperature of 160°C.
IS31LT3117 features a PWM/enable input which can
be used to realize PWM dimming of the LEDs. In
addition, the enable input can be used to put the
device into a low power consumption shutdown mode.
In shutdown, the device consumes only 80µA of supply
current.
VCC
The VCC input pin provides power to the internal
circuitry of the entire chip. The device supply current
will vary with the output current setting due to the
internal reference currents generated for each channel.
The nominal supply current is 11.5mA (R_SET=5.8kΩ)
during operation.
ISET
The output current for the IS31LT3117 is set by
connecting a resistor from the ISET pin to GND. An
internal 1.27V reference voltage source will supply a
current to the external current setting resistor. The
reference current is internally amplified by a gain of
1600 to each of the 4 outputs. In order to have an
accurate current output, this current setting resistor
must be mounted as close to ISET and AGND pins as
possible.
PWM
When the PWM input pin is at low state (V_PWM < 0.4V)
and stays low for more than 3.5ms, the IS31LT3117
enters a low power consumption mode with all of the
outputs turned OFF. In this mode, the IS31LT3117
consumes only 80µA of supply current. When the
PWM input pin is at high state (V_PWM > 1.4V), the
IS31LT3117 will enters in operation mode to resume
normal operation and all outputs are turned ON. A
PWM input signal to the PWM pin can be used for
HBLED dimming control. The recommended frequency
range of PWM signal is 4kHz ~ 100kHz.
GND
Signal ground current return pin.
PGND
Power ground current return pin. This pin should be
connected to as large as possible of a copper pad on
Integrated Silicon Solution, Inc. – www.issi.com
Rev.0C, 06/19/2014
the PCB to allow the best possible thermal
performance of the circuit.
VLEDx
Constant current regulator channel. Each of the 4 input
pins are capable of sinking up to 350mA of current with
a headroom voltage V_VLEDx of 0.8V (Min.).
It is recommended to maintain above a 0.8V V_VLEDx to
ensure a better line regulation of 350mA output
current.
OUTPUT CURRENT
The maximum sink current of all four channels are set
by a single resistor (R_SET) connected from the ISET pin
to ground. The maximum possible current is 350mA
per channel. However, any of the four channels can be
connected in parallel to allow a larger current output.
The channel sink current can be calculated by the
following Equation (1):
I _SINKx
 1600  ^VISET
R_SET
(1)
Where V_ISET = 1.27V (Typ.)
R_SET need to be chosen 1% accuracy resistor with
enough power tolerance and good temperature
characteristic to ensure stable output current.
The following table shows examples of I_SINKX values for
various R_SET settings:
I_SINKx (mA)
R_SET (kΩ)
10
203
100
20.3
350
5.8
If less than 4 channels are required for a particular
application, it is recommended to combine channels
together to drive the LEDs. This will help to reduce the
individual internal bias currents and, thus, the overall
power consumption and heat dissipation of the device.
For example, it can be configured to combine two or
four channels to one channel to drive two or one string
of LEDs. If only three channels are used, the unused
channel should be connected to GND.
VREF
When time of sinking a high current from a voltage
source increases, the headroom voltage (V_VLEDx) on
the current sinks will also increase. This will cause an
increase in power dissipation at the current sink, which
may result in an increase of the package temperature.
V_VLEDx  V_CC  V_LEDS
(2)
Where V_LEDS = total LED V_F for the channel.
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