ISSI IS31LT3360 User manual

IS31LT3360 AIC LED Driver Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com
R1.1, 3/22/2011
1
Description
The IS31LT3360 is a continuous mode inductive
step-down converter, designed for driving a single LED
or multiple series connected LEDs efficiently from a
voltage source higher than the LED voltage. The chip
operates from an input supply between 6V and 40V and
provides an externally adjustable output current of up to
1.2A. The IS31LT3360 includes an integrated output
switch and a high-side output current sensing circuit,
which uses an external resistor to set the nominal
average output current. Output current can be adjusted
linearly by applying an external control signal to the
ADJ pin. The ADJ pin will accept either a DC voltage or
a PWM waveform. This will provide either a continuous
or a gated output current. Applying a voltage of 0.2V or
lower to the ADJ pin turns the output off and switches
the chip into a low current standby state. The chip is
assembled in SOT89-5 package. IS31LT3360 AIC
DEMO board is used in RGB lamp or the general LED
lamp.
Features
Internal 40V power switch
6V to 40V VIN
Open-circuit protection
Thermal shutdown protection
I
OUTPUT =1.2A (max output current)
98% efficiency (max)
1200:1 dimming rate (typical)
3% IOUTPUT accuracy (typical)
PWM and DC line control mechanism
•Single pin On/Off
•Brightness control
1MHz switching frequency (max)
SOT89-5 package
Low part count and system resource overhead
Quick Start
Figure 1: IS31LT3360 AIC Evaluation Board Photo
Recommended Equipment
60VDC power supply
3 x LED panel (1W LED, 10 LEDs in series on
each panel)
Multi-meter
Recommended I/O Ratings
Input: 6-40VDC
Output: 1-10 LEDs in series (333mA)
Note: The input voltage must be 5V higher than the output
voltage (∑VF).
Absolute Maximum Ratings
Input voltage ≤40VDC
Caution: Do not exceed the conditions listed above, otherwise
the board will be damaged.
Ordering Information
Part No Temperature Range IC Package
IS31LT3360-SDLS3-EBAIC -40 to +85C (Industrial) SOT89-5
Table 1: IS31LT3360 AIC Ordering Information
For information about ordering, delivery, and pricing, please contact ISSI at
[email protected] or [phone].

IS31LT3360 AIC LED Driver Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com
R1.1, 3/22/2011
2
Procedure
The IS31LT3360 AIC evaluation board is fully assembled and tested. Follow the steps listed below to verify board
operation.
Caution: Do not turn on the power supply until all connections are completed.
1. Connect the terminals of the power supply to the AC1 and AC2 pin(If the board don’t have the rectifier(D1-D4),
Connect the positive terminal of the power supply to the DC+ of the board and the negative terminal of power
supply to the DC- of the board) .
2. Connect the negative of the one of LED panel (LED arrays) to the LED1- terminal. And connect the positive of
the same LED panel (LED arrays) to the LED1+ terminal.
3. Connect the other two LED panels to LED2 and LED3 as above.
4. Turn on the power supply to drive LED current and watch for lighting.
Figure 2: IS31LT3360 AIC Application Schematic
Application Notes
C8-10 are optional components that enhance filtering of noise coupling from ADJ pin.
D4-6 are optional component that serve to protect the IC during heavy load surge during the power on phase.
Bill of Materials
Name Description Symbol Qty Supplier Part No.
Capacitor Aluminum, 220uF,50V C0 1
Capacitor 100nF,50V, Surface-mount C1,C2,C3 3
Capacitor 10nF,50V, Surface-mount C4,C5,C6 3
Resistor 6.8KΩ±5%,0805, Surface-mount R4,R5,R6 3
Resistor 1KΩ±5%,0805, Surface-mount R7,R8,R9 3
Resistor 0.3Ω±1%,0805, Surface-mount R1,R2,R3 3
Diode Schottky, SS26,2A,60V D1-D3,D7-D10 7
Zener Diode Zener, 39V,0.25W D4,D5,D6 3
Inductor 47uH,Isat≥600A, Surface-mount L1,L2,L3 3
Driver Inductive Step-down LED Driver U1,U2,U3 3 ISSI IS31LT3360 AIC
Table 2: Bill of Materials; Refer to Figure 2.
LEDS D1
L1
GND
ADJ
VIN ISENSE LX
R1
U1
C0
C1
LEDS D2
L2
GND
ADJ
VIN ISENSE LX
R2
U2
C2
LEDS D3
L3
GND
ADJ
VIN ISENSE LX
R3
U3
C3
R4 R5 R6
D4 D6
D5
R7
C4
PWM1
R8
C5
PWM2
R9
C6
PWM3
AC/DC
D9
D7 D8
D10

IS31LT3360 AIC LED Driver Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com
R1.1, 3/22/2011
3
Detailed Description
LED Current Control
The nominal average output current in the LED(s) is
determined by the value of the external current sense
resistor (RS) connected between VIN and ISENSE and in is
given by:
 . 

;0.082
The table below gives values of nominal average
output current for several preferred values of current
setting resistor (Rs) in Figure 2: Application Schematic.
RS(Ω)IOUT (mA)
0.082 1200
0.1 1000
0.15 667
0.3 333
Table 3: Current Sense Resistance vs. Nominal Output Current
Vsense is divided into two ranges for enhanced output
current accuracy, and is explained in bin 3 more in
depth. The above values assume a floating ADJ pin
and a nominal voltage VREF =1.2V. Note that
RS=0.082Ωis the minimum allowed value of sense
resistor under these conditions to maintain switch
current below the specified maximum value. It is
possible to use different values of RSif the ADJ pin is
driven from an external voltage.
Inductor Selection
Recommended inductances range from 47μH to 220μH.
Higher inductances are igher supply voltages and low
output current in order to minimize errors due to
switching delays, which result in increased ripple and
lower efficiency. Higher values of inductance also result
in a smaller change in output current over the supply
voltage range. The inductor should be mounted as
close to LX pin as possible with low resistance
connections to LX and VIN pins.
PCB Layout Guide
Decoupling capacitors and coil
It is particularly important to mount the coil and the
input decoupling capacitor close to the chip to minimize
parasitic resistance and inductance, which will degrade
efficiency. The input decoupling capacitor (0.1uF fixed)
must be placed as close to the Vin and GND pins as
possible. It is also important to take account of any
trace resistance in series with current sense resistor
RS.
LX pin
The LX pin of the chip is a fast switching node, so PCB
traces should be kept as short as possible. To minimize
ground 'bounce', the ground pin of the chip should be
soldered directly to the ground plane.
ADJ pin
The ADJ pin is a high impedance input, so when left
floating, PCB traces to this pin should be as short as
possible to reduce noise pickup. ADJ pin can also be
connected to a voltage between 1.2V~5V. In this case,
the internal circuit will clamp the output current at the
value which is set by ADJ=1.2V.
High voltage traces
Avoid running any high voltage traces close to the ADJ
pin, to reduce the risk of leakage due to board
contamination. Any such leakage may raise the ADJ
pin voltage and cause excessive output current. A
ground ring placed around the ADJ pin will minimize
changes in output current under these conditions.

IS31LT3360 AIC LED Driver Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com
R1.1, 3/22/2011
4
PCB Layout
Physical dimensions (L x W x H): 55mm x 21mm x 22mm
Figure3:PCBLayout-TopLayer Figure4:PCBLayout-BottomLayer
Figure 5: Component Placement Guide -Top Layer Figure 6: Component Placement Guide -Bottom Layer
Copyright © 2011 Integrated Silicon Solution, Inc. All rights reserved. ISSI reserves the right to make changes to this specification and
its products at any time without notice. ISSI assumes no liability arising out of the application or use of any information, products or
services described herein. Customers are advised to obtain the latest version of this device specification before relying on any
published information and before placing orders for products.
Integrated Silicon Solution, Inc. does not recommend the use of any of its products in life support applications where the failure or
malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or
effectiveness. Products are not authorized for use in such applications unless Integrated Silicon Solution, Inc. receives written
assurance to its satisfaction, that:
a.) the risk of injury or damage has been minimized;
b.) the user assume all such risks; and
c.) potential liability of Integrated Silicon Solution, Inc is adequately protected under the circumstances.