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PDF IS31LT3117 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3117 | |
| Descripción | 4-CHANNEL CONSTANT CURRENT REGULATOR | |
| Fabricantes | ISSI | |
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IS31LT3117
53V, 350MA, 4-CHANNEL CONSTANT CURRENT REGULATOR WITH OTP
GENERAL DESCRIPTION
The IS31LT3117 is a 4-channel, linear regulated,
constant current LED driver which can provide 4 equal
currents outputs of up to 350mA per channel to drive
high brightness LEDs over an input voltage range of
6V to 53V, while maintaining an output leakage current
of less than 1µA. The output current is easily
programmed using a single, tiny external resistor. The
outputs of the IS31LT3117 can be connected in
parallel to allow greater than 350mA output current.
The IS31LT3117 also features a PWM input to enable
simple dimming control using a digital control signal.
The recommended frequency range of the PWM signal
is 4kHz ~ 100kHz.
The IS31LT3117 provides a unique over temperature
protection scheme. A hard shutdown which turns off all
LED currents occurs if the die junction temperature
exceeds the maximum value of 160°C. However, as
the die junction temperature rises up to over 130°C
(Typ.), the output current will begin to roll off at a rate
of -2.22%/°C (Typ.). If the die temperature continues to
rise above the hard shutdown temperature threshold,
the LED currents will drop to zero. When temperature
returns to 140°C (Typ.) or below, the hard shutdown
protection is released and the chip will function again.
The IS31LT3117 also has an optional 2.5V reference
voltage output which is able to supply up to 10mA (typ.)
output current. This voltage may be used to drive the
base of the external BJTs for higher current
applications in such case, driving for a wide varying
input voltage is needed.
The IS31LT3117 is offered in eTSSOP-16 package
with operating temperature range of -40°C to +125°C.
TYPICAL APPLICATION CIRCUIT
FEATURES
Preliminary Information
June 2014
6V to 53V input supply voltage range
Up to 1.4A total output current
Over temperature protections
Thermal current regulation above 130°C
±3% output current matching between channels
PWM dimming and shutdown control input
Optional 2.5V output to drive external standoff BJTs
Very few external components
APPLICATIONS
Industrial LED lighting
Low EMI lighting applications
Low-side constant current regulator
Figure 1 IS31LT3117 Directly Driving 4 LED Strings
Integrated Silicon Solution, Inc. – www.issi.com
Rev.0C, 06/19/2014
1
1 page  
IS31LT3117
ABSOLUTE MAXIMUM RATINGS (NOTE 4)
VCC pin to GND
-0.3V ~ +56V
Voltage at PWM and VLEDx pins
-0.3V ~ +56V
Voltage at ISET pin
-0.3V ~ +6.0V
Current at VREF pin
Junction temperature, TJ
Storage temperature range, TSTG
Operating temperature range, TA
Power dissipation, PD(MAX) (Note 5)
Thermal resistance, junction to ambient, still air, θJA
ESD (HBM)
ESD (CDM)
10mA
-40°C ~ +160°C
-65°C ~ +150°C
−40°C ~ +125°C
2.5W
39.9°C/W
All pins pass 2kV, except all ground pin pass 1.5kV
All pins pass 750V, except Pin 1 passes 100V
Note 4:
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 5:
Detail information please refers to package thermal de-rating curve on Page 12.
ELECTRICAL CHARACTERISTICS
Valid are at VCC = 12V, typical value at 25°C, unless otherwise noted.
Symbol
Parameter
Conditions
Min. Typ. Max. Unit
VCC
RSET
ISINK
IIN
ISD
tSD
fPWM
VHR
ILEAKAGE
tRISE
tFALL
VISET
VPWMH
VPWML
Supply voltage range
The ISET resistance
Output current per channel
Quiescent Input supply current
Shutdown input current
The time of PWM pin keeping low
to shutdown the IC
The PWM dimming frequency
Recommended VLED output
voltage headroom
Leakage current per channel
Output current rise time
Output current fall time
ISET pin output voltage
PWM pin input logic high voltage
PWM pin input logic low voltage
RSET=5.8kΩ, PWM=High
VVLEDx=1V, TA = 25°C
RSET=5.8kΩ, PWM=High
RSET=203kΩ, PWM=High
PWM = Low, VCC=12V
VCC=12V
ISINK=350mA (Note 6)
PWM=Low, VVLEDx=53V
RSET=5.8kΩ, PWM=20kHz,
current rise from 10%~90%
(Note 7)
RSET=5.8kΩ, PWM=20kHz,
current fall down from
90%~10% (Note 7)
VPWM rising
VPWM falling
6.0
5.8
332.5
3.5
4
0.8
1.16
1.4
350
300
200
1.27
53
203
367.5
13.8
6.3
90
100
1
1.38
0.4
V
kΩ
mA
mA
µA
ms
kHz
V
µA
ns
ns
V
V
V
Integrated Silicon Solution, Inc. – www.issi.com
Rev.0C, 06/19/2014
5
5 Page 
IS31LT3117
To address this thermal condition, the IS31LT3117
integrates a 2.5V reference output which can be used
to drive the base of an external BJT. This turns on the
BJT and effectively clamps the voltage across the
IS31LT3117’s output driver to approximately 0.8V. The
power dissipation is then shared between the IC and
the standoff transistor. The VREF pin can source up to
10mA of current to drive 4 external BJT’s, one for each
channel.
OPERATION WITH EXTERNAL BJTS
In most of the applications, the largest power
dissipation will be caused by the current regulator. The
thermal dissipation is proportional to the headroom
voltage (VVLEDx) and the sink current flowing through it.
When VCC is much higher than the VLEDS or ISINKx is
large, the power dissipation of the IS31LT3117 will be
high. This condition may easily trigger the over
temperature protection (OTP). Using external standoff
BJTs can transfer the unwanted thermal power from
the current regulator channel to the BJTs (Figure 15).
Figure 15 IS31LT3117 with external BJTs
With the external BJTs, the voltage across VLEDx to
GND is given by Equation (3):
VVLEDx VREF VbeQ 5 Rx I beQx VbeQx
VREF
VbeQ 5
Rx
I SINKx
1
VbeQx
(3)
Where VbeQ5 and VbeQx are the base-emitter voltage of
Q5 and Qx, IbeQx is the base-emitter current of Qx. is
the gain of BJT.
In order to ensure the normal operation, the voltage
across VLEDx should not be lower than the minimum
headroom voltage, minimum VHD (0.8V). So,
VREF
VbeQ 5
Rx
I SINKx
1
VbeQx
VHD
Therefore,
Rx
VREF
VbeQ 5 VbeQx
I SINKx
VHD
1
(4)
Integrated Silicon Solution, Inc. – www.issi.com
Rev.0C, 06/19/2014
R5 can transfer the unwanted thermal power from Q5 to
itself. Assume the current thought Q5 is IQ5,
IQ5
X
4
1
I SINKx
1
(5)
The power on R5 can be given by Equation (6):
PR5 R5 IQ52
(6)
The power on Q5 can be given by Equation (7):
PQ5 VCC VREF VbeQ5 R5 IQ5 I Q5 (7)
An appropriate value of R5 should be chosen to ensure
the power dissipation on Q5 won’t exceed the power
rating of Q5. If the sum of total power of PR5 and PQ5 is
low enough, R5 can be shorted and all power
dissipates on Q5.
The power on Qx can be calculated by Equation (8):
PQx VCC VLEDS VVLEDx I SINKx
(8)
An appropriate value of Rx should be chosen to ensure
the power dissipation on Qx won’t exceed the power
rating of Qx.
All of these BJTs should be set to operate in the linear
region to ensure normal operation.
For example, assume ISINKx =350mA, VCC=12V, VLEDS
of three LEDs is 9.6V, the minimum of the selected
BJT is 200, the maximum base-emitter voltage of Q5
and Qx are all 0.7V, The minimum VREF pin output
voltage is 2.4V, The Vbe of BJT is approximately 0.7V.
Rx can be calculated from Equation (4):
Rx
VREF
VbeQ 5 VbeQx
I SINKx
VHD
1
2.4
0.7 0.7
0.35
0.8
115
200 1
By Equation (5),
IQ5
4
X
1
I SINKx
1
4
0.35
200 1
7mA
Therefore,
PS PQ5 PR5 VCC (VREF VbeQ5 ) IQ5
12 2.4 0.7 0.007 0.0721W
The PS is pretty low. So R5 can be eliminated.
And,
11
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