IS31LT3360

40V/1.2A LED DRIVER WITH INTERNAL SWITCH

January 2014

GENERAL DESCRIPTION FEATURES

The IS31LT3360 is a continuous mode inductive  Up to 1.2A output current
step-down converter, designed for driving a single  High efficiency (up to 98%)
LED or multiple series connected LEDs efficiently  Wide input voltage range: 6V ~ 40V
from a voltage source higher than the LED voltage.
The chip operates from an input supply between 6V  Internal 40V power switch
and 40V and provides an externally adjustable output  Simple low parts count
current of up to 1.2A.  Typical 3% output current accuracy (-40°C to
+105°C, IS31LT3360-SDLS3-TR)
The IS31LT3360 includes an integrated output
switch and a high-side output current sensing circuit,  Typical 5% output current accuracy (-40°C to
which uses an external resistor to set the nominal +125°C, IS31LT3360-SDLS4-TR)
average output current.  Single pin on/off and brightness control using
DC voltage or PWM
Output current can be adjusted linearly by applying
an external control signal to the ADJ pin. The ADJ  Up to 1MHz switching frequency
pin will accept either a DC voltage or a PWM  Inherent LED open-circuit/short-circuit
waveform. This will provide either a continuous or a protection
gated output current.  Thermal shutdown protection circuitry
Applying a voltage less than 0.2V to the ADJ pin  Up to 1200: 1 dimming ratio
turns the output off and switches the chip into a low
current standby state.
APPLICATIONS
The chip is assembled in SOT89-5 package. It
 Automotive and avionic lighting
operates from 6V to 40V over two temperature
 LED MR16, MR11 spot light
ranges of -40°C to +105°C and -40°C to +125°C.
 LED street light
 PAR light
 Industrial lighting
 Refrigeration lights
 Other LED lighting

APPLICATION CIRCUIT

Figure 1 Typical Application Circuit

Note: The capacitor, C2, can’t be removed. And it should be placed as close as possible to the VIN and GND pins, otherwise the
operation might be abnormal.

Integrated Silicon Solution, Inc. – www.issi.com 1

Rev. C, 12/22/2013
IS31LT3360
PIN CONFIGURATION
Package Pin Configuration

LX 1 5 VIN

SOT89-5 GND 2 Thermal Pad

ADJ 3 4 ISENSE

PIN DESCRIPTION
No. Pin Description
1 LX Drain of power switch.
2 GND Ground (0V).
Multi-function On/Off and brightness control pin:
* Leave floating for normal operation.(VADJ = VREF = 1.2V giving
nominal average output current IOUT(NOM) =0.1/RS )
* Drive to voltage below 0.2V to turn off output current
3 ADJ * Drive with DC voltage (0.3V<VADJ <1.2V) to adjust output
current from 25% to 100% of IOUT_NOM
* Drive with PWM signal to adjust output current.
* When driving the ADJ pin above 1.2V, the current will be
clamped to 100% brightness automatically.
Connect resistor RS from this pin to VIN to define nominal
4 ISENSE
average output current IOUT_NOM =0.1/RS
Input voltage (6V ~ 40V). Decouple to ground with 0.1μF X7R
5 VIN
ceramic capacitor as close to device as possible.
Thermal Pad Connect to GND.

Integrated Silicon Solution, Inc. – www.issi.com 2

Rev. C, 12/22/2013
IS31LT3360
ORDERING INFORMATION
Industrial Range: -40°C to +105°C
Order Part No. Package QTY/Reel

IS31LT3360-SDLS3-TR SOT89-5, Lead-free 2500

Industrial Range: -40°C to +125°C

Order Part No. Package QTY/Reel

IS31LT3360-SDLS4-TR SOT89-5, Lead-free 2500

Copyright © 2014 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

Integrated Silicon Solution, Inc. – www.issi.com 3

Rev. C, 12/22/2013
IS31LT3360
ABSOLUTE MAXIMUM RATINGS (NOTE 1)
Input voltage, VIN -0.3V ~ +50V
VIN-5V ~ VIN+0.3V, VIN≥5V
ISENSE voltage, VSENSE
-0.3V ~ VIN+0.3V, VIN<5V
LX output voltage, VLX -0.3V ~ +50V
Adjust pin input voltage, VADJ -0.3V ~ +6.0V
Switch output current, ILX 1.5A
Power dissipation, PD(MAX) (Note 2) 0.94W
-40°C ~ +105°C, IS31LT3360-SDLS3-TR
Operating temperature, TA = TJ
-40°C ~ +125°C, IS31LT3360-SDLS4-TR
Storage temperature, TST -55°C ~ +150°C
Junction temperature, TJMAX 150°C
Junction to ambient, θJA 132.6°C/W
ESD (HBM) 4kV
ESD (CDM) 750V
Note 1:
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only and
functional operation of the device at these or any other condition beyond those indicated in the operational sections of the specifications is not
implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Note 2:
Detail information please refer to package thermal de-rating curve on Page 12.

ELECTRICAL CHARACTERISTICS
Valid are at VIN =12V, typical value at 25°C, unless otherwise noted.
○ Parameter range based on TA = -40°C ~ +125°C (Note 3)
The symbol in the table means these parameters are only available in the above temperature range.
Symbol Parameter Conditions Temp. Min. Typ. Max. Unit
VIN Input voltage 6 40 V
Quiescent supply current with output 80 120 160
IINQ_OFF ADJ pin grounded μA
off ○ 60 120 200
Quiescent supply current with output 450 600
IINQ_ON ADJ pin floating μA
switching ○ 450 680
Mean current sense threshold 97 100 103
VSENSE mV
voltage ○ 95 100 105
VSENSEHYS Sense threshold hysteresis ±15 %
ISENSE ISENSE pin input current VSENSE =VIN-0.1V 8 μA
Measured on ADJ
VREF Internal reference voltage 1.2 V
pin with pin floating
External control voltage range on
VADJ 0.3 1.2 V
ADJ pin for dc brightness control
DC voltage on ADJ pin to switch 0.15 0.2 0.25
VADJ_OFF chip from active (on) state to VADJ falling V
quiescent (off) state ○ 0.11 0.2 0.29
DC voltage on ADJ pin to switch 0.2 0.25 0.3
VADJ_ON chip from quiescent (off) state to VADJ rising V
active (on) state ○ 0.16 0.25 0.34

Integrated Silicon Solution, Inc. – www.issi.com 4

Rev. C, 12/22/2013
IS31LT3360
ELECTRICAL CHARACTERISTICS (CONTINUED)
Valid are at VIN =12V, typical value at 25°C, unless otherwise noted.
○ Parameter range based on TA = -40°C ~ +125°C (Note 3)
The symbol in the table means these parameters are only available in the above temperature range.
Symbol Parameter Conditions Temp. Min. Typ. Max. Unit
Resistance between ADJ pin
RADJ 500 kΩ
and VREF
1
ILX_LEAK LX switch leakage current μA
○ 2.5
ILX_MEAN Continuous LX switch current (Note 4) 1.2 A
0.27 0.4
RLX LX switch ‘ON’ resistance Ω
○ 0.27 0.7
tON_MIN Minimum switch ‘ON’ time LX switch ‘ON’ 200 ns
tOFF_MIN Minimum switch ‘OFF’ time LX switch ‘OFF’ 200 ns
Internal comparator propagation
tPD (Note 4) 50 ns
delay
TSD Thermal shutdown temperature (Note 4) 150 °C
TSD_HYS Thermal shutdown hysteresis (Note 4) 20 °C
Note 3: Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified over -40°C to
+125°C temperature range, are guaranteed by design, characterization and process control.
Note 4: Guaranteed by design.

Integrated Silicon Solution, Inc. – www.issi.com 5

Rev. C, 12/22/2013
IS31LT3360
TYPICAL PERFORMANCE CHARACTERISTICS
3 4
L = 47μH L = 47μH
RS = 0.083Ω 3 RS = 0.17Ω
2
2
1 1LED
1 1LED

Error (%)
Error(%)

2LED
0 3LED 0 2LED
4LED
3LED
5LED -1 4LED 5LED
-1 6LED 7LED 6LED
8LED -2 7LED
9LED 10LED
-2 8LED
-3
9LED 10LED
-3 -4
5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40

Power Supply(V) Power Supply(V)

Figure 2 Output Current Error vs. Power Supply Figure 3 Output Current Error vs. Power Supply

100 100 10LED

9LED 10LED 6LED 7LED 8LED 9LED
L = 47μH 6LED 7LED 8LED
RS = 0.083Ω 4LED 5LED 4LED 5LED
95 95 3LED
3LED
2LED
90 2LED 90
Efficiency (%)
Efficiency (%)

85 85 1LED
1LED

80 80

75 75
L = 47μH
RS = 0.17Ω
70 70
5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40

Power Supply(V) Power Supply(V)

Figure 4 Efficiency vs. Power Supply Figure 5 Efficiency vs. Power Supply

600 400
Operating Mode Shutdown Mode
500
Supply Current (µA)
Supply Current (µA)

300
400

300 200

200
100

100

0 0
6 10 15 20 25 30 35 40 6 10 15 20 25 30 35 40

Power Supply(V) Power Supply(V)

Figure 6 Supply Current vs. Power Supply (Operating Mode) Figure 7 Supply Current vs. Power Supply (Shutdown Mode)

Integrated Silicon Solution, Inc. – www.issi.com 6

Rev. C, 12/22/2013
IS31LT3360
1145 1150
Low Supply Voltage Normal Supply Voltage

1143 1146

VREF Voltage (mV)

VREF Voltage (mV)

1141 1142

1139 1138

1137 1134

1135 1130
6 7 8 9 10 6 10 15 20 25 30 35 40

Power Supply(V) Power Supply(V)

Figure 8 VREF vs. Power Supply (Low Supply Voltage) Figure 9 VREF vs. Power Supply (Normal Supply Voltage)

105 1200
VIN = 12V VIN = 12V
104

103 1190
VSENSE Voltage (mV)

102

101 1180
VADJ (mV)

100

99 1170

98

97 1160

96

95 1150
-40 -25 -10 5 20 35 50 65 80 95 110 125 -40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature (°C) Temperature (°C)

Figure 10 VSENSE vs. Temperature Figure 11 VADJ vs. Temperature

400
VIN = 12V
VIN = 12V
350 L = 47µH
RS = 0.2Ω
300

250
RDS_ON (mΩ)

200

150

100
IL
100mA/Div
50

0 VADJ
-40 -25 -10 5 20 35 50 65 80 95 110 125 1.0V/Div

Temperature (°C) Time (4µs/Div)

Figure 12 RDS_ON vs. Temperature Figure 13 ADJ Pin Voltage vs. IL

Integrated Silicon Solution, Inc. – www.issi.com 7

Rev. C, 12/22/2013
IS31LT3360

VIN = 12V
L = 47µH
RS = 0.2Ω

LED Open

IL VIN = 12V
100mA/Div L = 47µH
IL RS = 0.2Ω
100mA/Div LED Short

VLED
VLX 2V/Div
5V/Div
Time (1s/Div) Time (400ms/Div)

Figure 14 LED Open-Circuit Protection Figure 15 LED Short-Circuit Protection

Integrated Silicon Solution, Inc. – www.issi.com 8

Rev. C, 12/22/2013
IS31LT3360
FUNCTIONAL BLOCK DIAGRAM

Integrated Silicon Solution, Inc. – www.issi.com 9

Rev. C, 12/22/2013
IS31LT3360
APPLICATION INFORMATION
SETTING NOMINAL AVERAGE OUTPUT the current will be clamped to 100% brightness
CURRENT WITH EXTERNAL RESISTOR R S automatically.
The nominal average output current in the LED(s) is The input impedance of the ADJ pin is 500kΩ (Typ.).
determined by the value of the external current sense
OUTPUT CURRENT ADJUSTMENT BY PWM
resistor (RS) connected between VIN and ISENSE
CONTROL
pins and in is given by Equation (1):
Directly Driving ADJ Input
0.1
I OUT _ NOM  (1) A Pulse Width Modulated (PWM) signal with duty
RS cycle DPWM can be applied to the ADJ pin, as shown
Note that RS=0.083Ω is the minimum allowed value in Figure 17, to adjust the output current to a value
of sense resistor under these conditions to maintain below the nominal average value set by resistor RS,
the signal range is from 0V~5V.The logic “HIGH” is
switch current below the specified maximum value. It
is possible to use different values of RS if the ADJ pin higher than 1.2V, the logic “LOW” is lower than
0.2V.The PWM signal must have the driving ability to
is driven from an external voltage.
drive internal 500kΩ pull-up resistor.
The table below gives values of nominal average
output current for several preferred values of current
setting resistor (RS) in the typical application circuit
Figure 1:

Nominal Average Output

RS (Ω)
Current (mA) Figure 17 PWM Dimming Control Via ADJ Pin
0.083 1200 Driving The ADJ Input From A Microcontroller
0.15 667 Another possibility is to drive the chip from the open
0.3 333 drain output of a microcontroller. The Figure 18
below shows one method of doing this:
The above values assume that the ADJ pin is floating
and at a nominal voltage of VREF =1.2V.
Rs need to be chosen 1% accuracy resistor with
enough power tolerance and good temperature
characteristic to ensure stable output current.
OUTPUT CURRENT ADJUSTMENT BY
Figure 18 Dimming By MCU
EXTERNAL DC CONTROL VOLTAGE
The diode and resistor suppress possible high
The ADJ pin can be driven by an external DC voltage
amplitude negative spikes on the ADJ input resulting
(VADJ), as shown in Figure 16, to adjust the output
current to a value above or below the nominal from the drain-source capacitance of the FET.
Negative spikes at the input to the chip should be
average value defined by RS.
avoided as they may cause errors in output current or
erratic device operation.
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 120μA nominal.

Figure 16 Dimming by External DC Voltage INHERENT OPEN-CIRCUIT LED PROTECTION

The nominal average output current in this case is If the connection to the LED(s) is open-circuited, the
given by Equation (2): coil is isolated from the LX pin of the chip, so the chip
will not be damaged, unlike in many boost converters,
0.083  V ADJ where the back EMF may damage the internal switch
I OUT _ DC  (2) by forcing the drain above its breakdown voltage.
RS
CAPACITOR SELECTION
For 0.3V< VADJ <1.2V.
A low ESR capacitor should be used for input
Note that 100% brightness setting corresponds to decoupling, as the ESR of this capacitor appears in
VADJ = VREF. When driving the ADJ pin above 1.2V,
Integrated Silicon Solution, Inc. – www.issi.com 10
Rev. C, 12/22/2013
IS31LT3360
series with the supply source impedance and lowers L  I
overall efficiency. This capacitor has to supply the t OFF  (5)
relatively high peak current to the coil and smooth the
VLED  VD  I AVG ( RL  RS )
current ripple on the input supply. Note: tOFF_MIN > 200ns.
If the source is DC supply, the capacitor is decided Where:
by ripple of the source, the value is given by Equation
(3): L is the coil inductance (H)

I F  tON RL is the coil resistance (Ω)

C MIN  (3)
U MAX IAVG is the required LED current (A)
∆I is the coil peak-peak ripple current (A) {Internally
IF is the value of output current， U MAX is the ripple set to 0.3 × IAVG}
of power supply. tON is the “ON” time of MOSFET.
VIN is the supply voltage (V)
The value is higher than the minimum value. A
VLED is the total LED forward voltage (V)
100µF capacitor is recommended.
RLX is the switch resistance (Ω)
If the source is an AC supply, typical output voltages
ripple from a nominal 12V AC transformer can be VD is the diode forward voltage at the required load
±10%.If the input capacitor value is lower than 220μF, current (V)
the AC input waveform is distorted, sometimes the
Example:
lowest value will be lower than the forward voltage of
LED strings. This lower the average current of the For VIN=12V, L=47μH, RL=0.26Ω, VLED=3.4V, IAVG
LEDs. So it is recommended to set the value of the =333mA, VD =0.36V, RS = 0.3Ω, RLX=0.27Ω:
capacitor bigger than 220µF.
47  0.3  0.333
INDUCTOR SELECTION t ON   0.564 s
12  3.4  0.333  (0.3  0.26  0.27)
Recommended inductor values for the IS31LT3360 47  0.3  0.333
are in the range 47μH to 220μH. t OFF   1.19 s
3.4  0.36  0.333  (0.26  0.3)
Higher values of inductance are recommended at
higher supply voltages and low output current in This gives an operating frequency of 570kHz and a
order to minimize errors due to switching delays, duty cycle of 32%.
which result in increased ripple and lower efficiency.
Optimum performance will be achieved by setting the
Higher values of inductance also result in a smaller
duty cycle close to 50% at the nominal supply voltage.
change in output current over the supply voltage
This helps to equalize the undershoot and overshoot
range. The inductor should be mounted as close to
and improves temperature stability of the output
the chip as possible with low resistance connections
current.
to the LX and VIN pins.
DIODE SELECTION
The chosen coil should have a saturation current
higher than the peak output current and a continuous For maximum efficiency and performance, the
current rating above the required mean output rectifier (D1) should be a fast low capacitance
current. It is recommended to use inductor with Schottky diode with low reverse leakage at the
saturation current bigger than 1.2A for 700mA output maximum operating voltage and temperature.
current and inductor with saturation current bigger
than 500mA for 350mA output current. If alternative diodes are used, it is important to select
parts with a peak current rating above the peak coil
The inductor value should be chosen to maintain current and a continuous current rating higher than
operating duty cycle and switch 'on/off' times within the maximum output load current. It is very important
the specified limits over the supply voltage and load to consider the reverse leakage of the diode when
current range. operating at high temperature. Excess leakage will
increase the power dissipation in the device.
The following equations can be used as a guide.
The higher forward voltage and overshoot due to
LX Switch 'ON' time:
reverse recovery time in silicon diodes will increase
L  I the peak voltage on the LX output. If a silicon diode is
t ON  (4) used, care should be taken to ensure that the total
VIN  VLED  I AVG ( RS  RL  RLX ) voltage appearing on the LX pin including supply
Note: tON_MIN > 200ns. ripple, does not exceed the specified maximum
value.
LX Switch 'OFF' time:
Integrated Silicon Solution, Inc. – www.issi.com 11
Rev. C, 12/22/2013
IS31LT3360
REDUCING OUTPUT RIPPLE To ensure the performance, the die temperature (TJ)
of IS31LT3360 should not exceed 125°C. The graph
A value of 1μF will reduce nominal ripple current by a
below gives details for power derating.
factor three (approx.). Proportionally lower ripple can
1
be achieved with higher capacitor values. Note that
the capacitor will not affect operating frequency or SOT89-5
efficiency, but it will increase start-up delay, by

Power Dissipation (W)

0.8
reducing the rate of rise of LED voltage.
OPERATION AT LOW SUPPLY VOLTAGE 0.6
The internal regulator disables the drive to the switch
until the supply has risen above the startup threshold 0.4
set internally which makes power MOSFET
on-resistance small enough. Above this threshold,
the chip will start to operate. However, with the 0.2
supply voltage below the specified minimum value,
the switch duty cycle will be high and the chip power
0
dissipation will be at a maximum. Care should be -40 -25 -10 5 20 35 50 65 80 95 110 125
taken to avoid operating the chip under such
conditions in the application, in order to minimize the Temperature (°C)
risk of exceeding the maximum allowed die Figure 19 PD vs. TA
temperature. (See next section on thermal
considerations). It will also increase if the efficiency of the circuit is low.
This may result from the use of unsuitable coils, or
Note that when driving loads of two or more LEDs, excessive parasitic output capacitance on the switch
the forward drop will normally be sufficient to prevent output.
the chip from switching below approximately 6V. This
will minimize the risk of damage to the chip. LAYOUT CONSIDERATIONS

THERMAL CONSIDERATIONS VIN Pin

When operating the chip at high ambient The GND of power supply usually have some
temperatures, or when driving maximum load current, distance to the chip GND pin, which cause parasitic
care must be taken to avoid exceeding the package resistance and inductance. It causes ground voltage
power dissipation limits. The maximum power bounce while the MOSFET is switching. Connect a
dissipation can be calculated using the following 0.1µF capacitor C2 as close to device as possible to
Equation (6): minimize the ground bounce.

TJ ( MAX )  TA LX Pin
PD ( MAX )  (6) The LX pin of the chip is a fast switching node, so
 JA
PCB traces should be kept as short as possible. To
Where TJ(MAX) is the maximum junction temperature, minimize ground 'bounce', the ground pin of the chip
TA is the ambient temperature, and θJA is the junction should be soldered directly to the ground plane.
to ambient thermal resistance. Coil And Decoupling Capacitor C 1
The recommended maximum operating junction It is particularly important to mount the coil and the
temperature, TJ(MAX), is 150°C and so maximum input decoupling capacitor close to the chip to
ambient temperature is determined by the junction to minimize parasitic resistance and inductance, which
ambient thermal resistance, θJA. will degrade efficiency. It is also important to take
Therefore the maximum power dissipation at TA = account of any trace resistance in series with current
25°C is: sense resistor RS.

150C  25C ADJ Pin

PD ( MAX )   0.94W
132.6C / W 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 VADJ = 1.2V.

Integrated Silicon Solution, Inc. – www.issi.com 12

Rev. C, 12/22/2013
IS31LT3360
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 affect the ADJ
pin voltage and cause unexpectable output current.
The IS31LT3360 has external protection circuitry to
prevent excessive output current if ADJ voltage rises
above 1.2V. A ground ring placed around the ADJ
pin will minimize changes in output current under
these conditions.

Integrated Silicon Solution, Inc. – www.issi.com 13

Rev. C, 12/22/2013
IS31LT3360
CLASSIFICATION REFLOW PROFILES
Profile Feature Pb-Free Assembly

Preheat & Soak

150°C
Temperature min (Tsmin)
200°C
Temperature max (Tsmax)
60-120 seconds
Time (Tsmin to Tsmax) (ts)

Average ramp-up rate (Tsmax to Tp) 3°C/second max.

Liquidous temperature (TL) 217°C
Time at liquidous (tL) 60-150 seconds
Peak package body temperature (Tp)* Max 260°C
Time (tp)** within 5°C of the specified
Max 30 seconds
classification temperature (Tc)
Average ramp-down rate (Tp to Tsmax) 6°C/second max.
Time 25°C to peak temperature 8 minutes max.

Figure 20 Classification Profile

Integrated Silicon Solution, Inc. – www.issi.com 14

Rev. C, 12/22/2013
IS31LT3360
PACKAGE INFORMATION

SOT89-5

Note: All dimensions in millimeters unless otherwise stated.

Integrated Silicon Solution, Inc. – www.issi.com 15

Rev. C, 12/22/2013