IS31LT3350-V2STLS2-TR ISSI, IS31LT3350-V2STLS2-TR Datasheet - Page 8

• Manufacturer Part Number: IS31LT3350-V2STLS2-TR
• Description: LED Lighting Drivers 40V LED Drvr w/ intrnl switch
• Manufacturer: ISSI

Specifications of IS31LT3350-V2STLS2-TR

• Input Voltage: 6 V to 40 V
• Operating Frequency: 154 kHz
• Maximum Supply Current: 80 uA
• Output Current: 400 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23-5
• Factory Pack Quantity: 3000

IS31LT3350
APPLICATION INFORMATION
Setting nominal average output current with external
resistor R
The nominal average output current in the LED(s) is
determined by the value of the external current sense
resistor (R
given by:
I
The table below gives values of nominal average output
current for several preferred values of current setting
resistor (R
page 1:
R
0.13
0.15
0.27
0.3
Vsense is divided into two ranges to improve current
accuracy, please refer to bin information on page 3.
The above values assume that the ADJ pin is floating and
at a nominal voltage of V
Note that R
sense resistor under these conditions to maintain switch
current below the specified maximum value.
It is possible to use different values of R
driven from an external voltage.
Output current adjustment by external DC
control voltage
The ADJ pin can be driven by an external dc voltage
(V
above or below the nominal average value defined by R
The nominal average output current in this case is given
by:
I
Note that 100% brightness setting corresponds to V
V
will be clamped to 100% brightness automatically.
The input impedance of the ADJ pin is 500kΩ ±25% .
Output current adjustment by PWM control
Directly driving ADJ input
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 10/18/2011
OUT nom
OUTdc
REF
S
ADJ
(Ω)
. When driving the ADJ pin above 1.2V, the current
), as shown, to adjust the output current to a value
= 0.083*V
GND
DC
= 0.1/R
S
S
S
) connected between V
Nominal average
output current (mA)
769
667
370
333
S
) in the typical application circuit shown on
=0.13Ω is the minimum allowed value of
S
ADJ
[for R
/R
ADJ
S
[for 0.3V< V
REF
S
>0.13Ω]
=1.2V.
IS31LT3350
IN
GND
and I
ADJ
S
if the ADJ pin is
SENSE
<1.2V]
and is
ADJ
=
S
.
A Pulse Width Modulated (PWM) signal with duty cycle
D
adjust the output current to a value below the nominal
average value set by resistor R
0V~5V. The PWM signal must have the driving ability to
drive the internal 500KΩ pull-up resistor.
Driving the ADJ input from a microcontroller
Another possibility is to drive the chip from the open drain
output of a microcontroller. The diagram below shows
one method of doing this:
The diode and resistor suppress possible high amplitude
negative spikes on the ADJ input resulting from the
drain-source capacitance of the FET. Negative spikes at
the input to the chip should be avoided as they may
cause errors in output current or erratic device operation.
See the section on PWM dimming for more details of the
various modes of control using high frequency and low
frequency PWM signals.
Shutdown mode
Taking the ADJ pin to a voltage below 0.2V will turn off
the output and supply current will fall to a low standby
level of 60μA nominal.
Inherent open-circuit LED protection
If the connection to the LED(s) is open-circuited, the coil
is isolated from the LX pin of the chip, so the chip will not
be damaged, unlike in many boost converters, where the
back EMF may damage the internal switch by forcing the
drain above its breakdown voltage.
Capacitor selection
A low ESR capacitor should be used for input decoupling,
as the ESR of this capacitor appears in series with the
supply source impedance and lowers overall efficiency.
This capacitor has to supply the relatively high peak
current to the coil and smooth the current ripple on the
input supply.
PWM
MCU
can be applied to the ADJ pin, as shown below, to
GND
10K
ADJ
S
, the signal range is from
IS31LT3350
GND
8