IS32LT3126
150MA DUAL CHANNEL LED DRIVER WITH FAULT DETECTION
May 2018
GENERAL DESCRIPTION
FEATURES
The IS32LT3126 is a dual linear programmable current
regulator consisting of 2 independently controlled
output channels; each channel is capable of sourcing
150mA. Both channels can be combined to provide a
total of 300mA. It supports PWM dimming of both
channels via power supply modulation (PSM). It also
features ENx pins to individually PWM dim and
independently adjust the average output current for
each channel. The max current for each channel is set
with its corresponding external resistor.
The UVx pins set the VCC under voltage lockout of
each channel to match the LED stack for high side
PWM dimming operation. In addition, the IC integrates
fault protection for LED open/short, ISETx pin
open/short and over temperature condition for robust
operation. Detection of these failures is reported by
FAULTB pin. When a fault is detected the device will
disable itself and output an open drain low signal.
Multiple devices can have their FAULTB pins
connected to create a “one-fail-all-fail” condition. For
multiple LED string applications, the device can detect
a single LED short. The single LED short detection is
set by a resistor divider on the STx pins. A single LED
short failure is reported by the separate FAULTB_S
pin.
The IS32LT3126 is targeted at the automotive market
with end applications to include interior and exterior
lighting. For 12V automotive applications the low
dropout driver can support one to several LEDs on the
output channels. It is offered in a small thermally
enhanced eTSSOP-16 package.
Dual channel: each channel can source up to
150mA and the two channels combined to source
up to 300mA
External resistors individually set source current
4% channel to channel current matching
Individually programmable VCC under voltage
lockout to match the LED stack for PSM operation
Individual PWM dimming
Shared fault flag for multiple devices operation
Fault protection with flag reporting:
- Single LED short (optional to turn off all LEDs)
- LED string open/short
- OUTx pins short to VCC/GND
- ISETx pins open/short
- Over temperature current rollback (no reporting)
- Thermal shutdown
External CSTOR capacitor keeps fault status during
start/stop operation
eTSSOP-16 package
Operating temperature range from -40°C ~ +125°C
AEC-Q100 qualification
APPLICATIONS
Automotive interior/exterior lighting:
- Turn signal light
TYPICAL APPLICATION CIRCUIT
Figure 1
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Rev. A, 05/08/2018
Typical Application Circuit
1
IS32LT3126
Figure 2
Typical Application Circuit (Several Devices In Parallel with FAULTB Interlinkage)
Note 1: For PSM dimming application, high CVCC capacitor value will affect the dimming accuracy. To get better dimming performance,
recommend 0.1µF for it.
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Rev. A, 05/08/2018
2
IS32LT3126
PIN CONFIGURATION
Package
Pin Configuration (Top View)
eTSSOP-16
PIN DESCRIPTION
No.
Pin
Description
1
GND
Ground.
2
CSTOR
Keep-alive capacitor to maintain the deglitch timer and fault latch
status with collapsing VCC.
3
ISET1
Output current setting for channel 1. Connect a resistor between
this pin and GND to set the maximum output current.
4
ISET2
Output current setting for channel 2. Connect a resistor between
this pin and GND to set the maximum output current.
5
FAULTB_S
Open drain fault reporting output with internal pull up to 4.5V.
Indicate the fault condition of single LED short.
6
FAULTB
Open drain fault reporting output with internal pull up to 4.5V.
Indicate the fault conditions except single LED short. This pin is
also an input pin. Pulling this pin low will shutdown the device.
7
ST1
LED string voltage monitor pin of OUT1 to achieve single LED
short detection.
8
OUT1
Output current source channel 1.
9
OUT2
Output current source channel 2.
10
ST2
LED string voltage monitor pin of OUT2 to achieve single LED
short detection.
11
NC
Not connect.
12
VCC
Power supply input pin.
13
UV1
External under voltage lockout threshold detection pin for OUT1.
14
EN1
Enable pin of OUT1. It can be used to set OUT1 current by PWM.
15
UV2
External under voltage lockout threshold detection pin for OUT2.
16
EN2
Enable pin of OUT2. It can be used to set OUT2 current by PWM.
Thermal Pad
Must be electrically connected to GND plane for better thermal
dissipation.
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3
IS32LT3126
ORDERING INFORMATION
Automotive Range: -40°C to +125°C
Order Part No.
Package
QTY/Reel
IS32LT3126-ZLA3-TR
eTSSOP-16, Lead-free
2500
Copyright © 2018 Lumissil Microsystems. All rights reserved. Lumissil Microsystems reserves the right to make changes to this specification and its
products at any time without notice. Lumissil Microsystems 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.
Lumissil Microsystems 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 Lumissil Microsystems 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 Lumissil Microsystems is adequately protected under the circumstances
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Rev. A, 05/08/2018
4
IS32LT3126
ABSOLUTE MAXIMUM RATINGS
VCC, OUT1, OUT2, EN1, EN2, UV1, UV2, ST1, ST2
ISET1, ISET2, CTSOR, FAULTB, FAULTB_S
Ambient operating temperature, TA=TJ
Maximum continuous junction temperature, TJ(MAX)
Storage temperature range, TSTG
Maximum power dissipation, PDMAX
Package thermal resistance, junction to ambient (4 layer standard
test PCB based on JEDEC standard), θJA
Package thermal resistance, junction to thermal PAD (4 layer
standard test PCB based on JEDEC standard), θJP
ESD (HBM)
ESD (CDM)
-0.3V ~ +45V
-0.3V ~ +7.0V
-40°C ~ +125°C
+150°C
-65°C ~ +150°C
2.15W
46.5°C/W
1.617°C/W
±2kV
±750V
Note 2: 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.
ELECTRICAL CHARACTERISTICS
TJ = -40°C ~ +125°C, VCC=12V, the detail refer to each condition description. Typical values are at TJ = 25°C.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
42
V
4.8
V
Power Up Parameter
VCC
Supply voltage range
VUVLO
VCC under voltage lockout
threshold voltage
VUVLO_HY
VCC under voltage lockout
voltage hysteresis
5
Voltage falling
4.2
4.5
200
ICC
VCC supply current
VENx= High, RISETx= 20kΩ
ISD
Shutdown current in normal
mode
VENx= Low, TJ= 25°C
ISD_FLT
Shutdown current in fault mode
VENx= High, FAULTB= Low
TJ= 25°C
tSD
Both of EN pins low time for IC
power shutdown
tON
EN high time for IC power up
3
40
mV
5.5
mA
1
2
mA
1
2
mA
48
55
ms
40
μs
IOUT= -150mA, VCC= 12V
VENx= High (Note 3)
Channel Parameter
VISETx
IOUT
VHR
The ISETx voltage
Output current per channel
(Note 4)
Minimum headroom voltage
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Rev. A, 05/08/2018
1
V
RISETx= 80kΩ, VHR= 1V
-27.5
-25
-22.5
RISETx= 20kΩ, VHR= 1V
-106
-100
-94
RISETx= 13.3kΩ, VHR= 1V
-159
-150
-141
VCC - VOUT, IOUT= -150mA
1100
VCC - VOUT, IOUT= -100mA
800
mA
mV
5
IS32LT3126
ELECTRICAL CHARACTERISTICS (CONTINUE)
TJ = -40°C ~ +125°C, VCC=12V, the detail refer to each condition description. Typical values are at TJ = 25°C.
Symbol
Parameter
Conditions
Min.
IOUT_R
Output current per channel
range
RISETx= 80kΩ, IOUT=-25mA
RISETx= 13.33kΩ, IOUT=-150mA
-150
IOUT_L
Output limit current per channel
RISETx=5kΩ
-290
∆IOUT
Current matching
RISETx=20kΩ
-4
tSL
Current slew time
Enable by ENx pin, current
rise/fall between 0%~100%
Leakage current per channel
VENx=Low, VOUT=0V, VCC=42V
ILEAK
Typ.
-230
Max.
Unit
-25
mA
-170
mA
4
%
4
μs
1
μA
Fault Protect Parameter
Fault deglitch time
Fault must be present at least this
long to trigger the fault detect
25
VFAULTB
FAULTB pin voltage
Sink current=20mA
0.2
0.4
V
RFAULTB
FAULTB pin internal pull up
210
300
KΩ
2
V
tFD
μs
VFAULTB_IH
FAULTB pin input high enable
threshold
VFAULTB_IL
FAULTB pin input low disable
threshold
VFAULTB_S
FAULTB_S pin voltage
Sink current=20mA
VSCD
OUTx pin short to GND
threshold
Measured at OUTx
VSCD_HY
OUTx pin short to GND
hysteresis
Measured at OUTx
VOCD
OUTx pin open threshold
Measured at (VCC-VOUTx)
VOCD_HY
OUTx pin open hysteresis
Measured at (VCC-VOUTx)
ICST
CSTOR pin leakage current
VCSTOR=5.5V
TRO
Thermal rollback threshold
(Note 3)
145
°C
TSD
Thermal shutdown threshold
(Note 3)
165
°C
THY
Over-temperature hysteresis
(Note 3)
25
°C
ENx input voltage threshold
Voltage rising
ENx input hysteresis
(Note 3)
fPWM
PWM frequency to ENx
(Note 3)
VUV
UVx input voltage threshold
Voltage rising
0.8
1.0
V
0.2
0.4
V
1.2
1.5
V
220
150
225
mV
300
100
5
mV
mV
10
μA
Logic Input
VEN
VENHY
VUVHY
VST
1.18
VSTHY
STx Input hysteresis
RSTPL
STx pull up resistor
1.28
40
1.18
UVx input hysteresis
STx input voltage threshold
1.23
1.23
mV
1
kHz
1.28
V
40
Voltage falling
VST=1V
1.12
1.16
V
mV
1.20
V
40
mV
500
kΩ
Note 3: Guaranteed by design.
Note 4: Output current accuracy is not intended to be guaranteed at output voltages less than 1.5V.
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IS32LT3126
TYPICAL PERFORMANCE CHARACTERISTICS
180
110
VCC = 12V
TJ = -40°C
160
Output Current (mA)
Output Current (mA)
VHR = 2V
RISET = 20kΩ
TJ = -40°C, 25°C, 125°C
105
100
95
RISET = 13kΩ
140
120
RISET = 20kΩ
100
80
RISET = 39kΩ
60
40
20
90
5
15
25
35
0
45
0
1
2
3
VCC = 12V
TJ = 25°C
160
140
RISET = 20kΩ
100
80
RISET = 39kΩ
60
3
4
5
6
7
8
9
0
1
2
3
VCC = 12V
VHR = 2V
RISET = 20kΩ
245
Output Current (mA)
Output Current (mA)
6
7
8
10
110
125
250
104
102
100
98
96
240
230
225
220
215
210
92
205
-25
-10
5
20
35
50
65
80
Temperature (°C)
Figure 7 IOUT vs. TJ
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Rev. A, 05/08/2018
95
110
125
VCC = 12V
VHR = 2V
RISET = 5.1kΩ
235
94
90
-40
5
Figure 6 IOUT vs. VHR
Figure 5 IOUT vs. VHR
110
106
4
Headroom Voltage (V)
Headroom Voltage (V)
108
9
RISET = 39kΩ
60
0
10
RISET = 20kΩ
80
20
2
10
100
20
1
9
RISET = 13kΩ
120
40
0
8
140
40
0
7
VCC = 12V
TJ = 125°C
RISET = 13kΩ
Output Current (mA)
Output Current (mA)
180
120
6
Figure 4 IOUT vs. VHR
Figure 3 IOUT vs. VCC
160
5
Headroom Voltage (V)
Supply Voltage (V)
180
4
200
-40
-25
-10
5
20
35
50
65
80
95
Temperature (°C)
Figure 8 IOUT_L vs. TJ
7
IS32LT3126
180
5.5
VCC = 12V
VHR = 2V
RISET = 13kΩ
5.4
140
Supply Current (mA)
Output Current (mA)
160
RISET = 20kΩ
120
100
80
60
40
RISET = 100kΩ
5.3
VCC = 12V
RISET = 20kΩ
EN = High
5.2
5.1
5
4.9
4.8
4.7
20
4.6
0
100
110
120
130
140
150
160
4.5
-40
170
-25
-10
5
Temperature (°C)
35
50
65
80
95
110
125
80
95
110
125
80
95
110
125
Temperature (°C)
Figure 9 IOUT vs. TA (Thermal Rolloff)
Figure 10 ICC vs. TJ
1
1.50
VCC = 12V
FAULTB = Low
1.45
0.9
Supply Current (mA)
Supply Current (mA)
20
0.8
0.7
VCC = 12V
EN = Low
1.40
1.35
1.30
1.25
1.20
1.15
1.10
0.6
1.05
0.5
-40
-25
-10
5
20
35
50
65
80
95
110
1.00
-40
125
-25
-10
5
35
50
65
Temperature (°C)
Temperature (°C)
Figure 12 ISD vs. TJ
Figure 11 ISD_FLT vs. TJ
1.05
1.04
20
1.25
VIH
VCC = 12V
VCC = 12V
RISET = 20kΩ
1.03
1.23
VEN (V)
VISET (V)
1.02
1.01
1.00
0.99
VIL
1.21
1.19
0.98
0.97
1.17
0.96
0.95
-40
-25
-10
5
20
35
50
65
80
Temperature (°C)
Figure 13 VISET vs. TJ
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Rev. A, 05/08/2018
95
110
125
1.15
-40
-25
-10
5
20
35
50
65
Temperature (°C)
Figure 14 VEN vs. TJ
8
IS32LT3126
4.8
1.25
VIH
VCC = 12V
1.24
VCC = 12V
4.75
1.23
4.7
1.21
VUVLO (V)
VUV (V)
1.22
VIL
1.2
1.19
VIH
4.65
4.6
4.55
VIL
1.18
4.5
1.17
4.45
1.16
1.15
-40
-25
-10
5
20
35
50
65
80
95
110
4.4
-40
125
-25
-10
Temperature (°C)
Figure 15 VUV vs. TJ
Output Current (mA)
VST (V)
65
80
95
110
125
VIH
1.16
1.15
VIL
1.13
80
70
60
50
40
30
1.12
20
1.11
10
-25
VCC = 12V
RISET = 20kΩ
PSM Dimming 1kHz
TJ = -40°C, 25°C, 125°C
90
1.14
-10
5
20
35
50
65
80
95
110
0
125
0
20
Temperature (°C)
40
60
80
100
PSM Duty Cycle (%)
Figure 17 VST vs. TJ
Figure 18 PSM Dimming at 1kHz
100
100
VCC = 12V
RISET = 20kΩ
PSM Dimming 500Hz
TJ = -40°C, 25°C, 125°C
80
VCC = 12V
RISET = 20kΩ
PSM Dimming 100Hz
TJ = -40°C, 25°C, 125°C
90
Output Current (mA)
90
Output Current (mA)
50
Figure 16 VUVLO vs. TJ
VCC = 12V
1.17
70
60
50
40
80
70
60
50
40
30
30
20
20
10
10
0
35
100
1.18
1.10
-40
20
Temperature (°C)
1.20
1.19
5
0
0
20
40
60
PSM Duty Cycle (%)
Figure 19 PSM Dimming at 500Hz
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Rev. A, 05/08/2018
80
100
0
20
40
60
80
100
PSM Duty Cycle (%)
Figure 20 PSM Dimming at 100Hz
9
IS32LT3126
100
100
VCC = 12V
RISET = 20kΩ
PWM Dimming 1kHz
TJ = -40°C, 25°C, 125°C
80
70
60
50
40
80
70
60
50
40
30
30
20
20
10
10
0
0
20
VCC = 12V
RISET = 20kΩ
PWM Dimming 500Hz
TJ = -40°C, 25°C, 125°C
90
Output Current (mA)
Output Current (mA)
90
40
60
80
100
0
0
20
40
PWM Duty Cycle (%)
60
80
100
PWM Duty Cycle (%)
Figure 21 PWM Dimming at 1kHz
Figure 22 PWM Dimming at 500Hz
100
Output Current (mA)
VCC = 12V
VHR = 2V
TJ = -40°C
VCC = 12V
RISET = 20kΩ
PWM Dimming 100Hz
TJ = -40°C, 25°C, 125°C
90
80
VEN
1V/Div
70
60
VISET1
1V/Div
50
40
30
VFAULTB
5V/Div
20
10
0
0
20
40
60
80
100
IOUT
50mA/Div
Time (4µs/Div)
PWM Duty Cycle (%)
Figure 24 EN On
Figure 23 PWM Dimming at 100Hz
VCC = 12V
VHR = 2V
TJ = 125°C
VCC = 12V
VHR = 2V
TJ = 25°C
VEN
1V/Div
VEN
1V/Div
VISET1
1V/Div
VISET1
1V/Div
VFAULTB
5V/Div
VFAULTB
5V/Div
IOUT
50mA/Div
IOUT
50mA/Div
Time (4µs/Div)
Figure 25 EN On
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Time (4µs/Div)
Figure 26 EN On
10
IS32LT3126
VEN
1V/Div
VCC = 12V
VHR = 2V
TJ = -40°C
VEN
1V/Div
VISET1
1V/Div
VISET1
1V/Div
VFAULTB
5V/Div
VFAULTB
5V/Div
IOUT
50mA/Div
IOUT
50mA/Div
Time (1µs/Div)
Time (1µs/Div)
Figure 27 EN Off
VEN
1V/Div
VCC = 12V
VHR = 2V
TJ = 25°C
VCC = 12V
VHR = 2V
TJ = 125°C
Figure 28 EN Off
VEN
2V/Div
VISET1
1V/Div
VCC = 12V
VHR = 2V
TJ = -40°C
VISET1
1V/Div
VISET2
1V/Div
VFAULTB
5V/Div
IOUT
50mA/Div
IOUT
50mA/Div
Time (1µs/Div)
Time 8ms/Div)
Figure 29 EN Off
VEN
2V/Div
VCC = 12V
VHR = 2V
TJ = 25°C
Figure 30 tSD
VEN
2V/Div
VISET1
1V/Div
VISET1
1V/Div
VISET2
1V/Div
VISET2
1V/Div
IOUT
50mA/Div
IOUT
50mA/Div
Time 8ms/Div)
VCC = 12V
VHR = 2V
TJ = 125°C
Time 8ms/Div)
Figure 31 tSD
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Rev. A, 05/08/2018
Figure 32 tSD
11
IS32LT3126
FUNCTIONAL BLOCK DIAGRAM
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Rev. A, 05/08/2018
12
IS32LT3126
APPLICATION INFORMATION
The IS32LT3126 is a 2-channel linear LED current
source optimized to drive automotive interior or
exterior LED light which can be dimmed via Power
Supply Modulation (PSM) or by digitally driving the EN
pin.
accept a PWM signal to implement LED dimming. LED
average current may be computed using the following
Equation (3).
Each of the 2 output channels is capable of 150mA.
The output current is set by two reference resistors
(RISETx); one for each channel.
IMAX is computed using Equation (1) and DPWM is the
duty cycle. To guarantee a reasonably good dimming
effect, recommend PWM frequency in the range of
100Hz ~ 1kHz. Driving the ENx pins with a PWM signal
can effectively adjust the LED intensity. The PWM
signal voltage levels must meet the ENx pins input
voltage levels, VEN. Tie them to VCC pin via a 10KΩ
resistor when ENx pins are unused; do not leave them
floating.
OUTPUT CURRENT SETTING
A single resistor (RISETx) controls the maximum output
current for each channel. The resistor value for a
specific current level is calculated using the following
Equation (1):
RISET
2000
I SET
(1)
(13.33kΩ≤RISET≤80kΩ)
RISET need to be chosen 1% accuracy resistor with
good temperature characteristic to ensure stable
output current.
The device is protected from an output overcurrent
condition caused by a too low value RISETx, by
internally limiting the maximum current to IOUT_L.
If only one channel is used, the EN pin of the unused
channel should be tied to GND to prevent unwanted
fault reporting.
I LED I MAX DPWM
(3)
UVx PINS OPERATION
The IC has an internal VCC UVLO set at VUVLO.
However, it may be desirable to externally set an
UVLO to track the number of LED’s used in the string.
For PSM dimming application, the higher UVLO will
track the PSM off time to a pre-determined VCC level.
In addition, it is necessary to prevent false LED open
detection due to the LED string losing its headroom
voltage, such as when VCC rises up from zero during
power up or PSM dimming. The UVx pin can be used
to independently set a VCC under voltage lockout
threshold via a resistor divider for each channel.
VBattery
POWER SUPPLY MODULATION DIMMING
The IS32LT3126 can operate with Power Supply
Modulation (PSM) where the device’s power supply is
pulse width modulated to achieve LED dimming. The
IS32LT3126 stability is not affected by operation with
PSM. To get better dimming linearity, the
recommended PSM frequency can be in the range of
100Hz to 300Hz, (200Hz Typ.) and input capacitor,
CVCC, should be low value (0.1µF Typ.) to ensure rapid
discharge during PSM low period.
CSTOR OPERATION
To keep the IC operating normally during condition of
PSM when VCC goes to zero, CSTOR capacitor provides
the keep-alive current needed to power the digital
counter and the fault flag circuits. A capacitor value of
2.2µF is recommended. The keep-alive time could be
roughly calculated by the following Equation (2):
t alive
2.5V C STOR
I CST
(2)
ENx PINS OPERATION
The voltage at the ENx pins must be higher than VEN to
enable the channel and below (VEN-VENHY) to disable
the channel. The ENx pins of the IS32LT3126 can
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Rev. A, 05/08/2018
VCC
PSM
R1
UVx
IS32LT3126
R2
Figure 33
UVx Pins Operation
This external UVLO threshold voltage can be
computed using the following Equation (4):
VCC _ UVLO VUV
R1 R2
R2
(4)
Any unused UVLO pin must be tied to VCC pin via a
10kΩ resistor; do not leave it floating.
To prevent false open detection, the external UVLO
threshold voltage should be set at Equation (5):
VCC _ UVLO VLED _ MAX VOCD
(5)
Where VLED_MAX is the maximum LED string forward
voltage on the output channel.
13
IS32LT3126
STx PINS OPERATION
IS32LT3126 device features single LED short
detection using a resistor divider on the STx pins. In
the case of any single LED short will result in that the
STx pin voltage to drop below the threshold voltage
VST and remains for tFD, the FAULTB_S pin pulls low to
report the failure to host and all channels continue
sourcing current. If FAULTB_S pin is tied to FAULTB
pin, the FAULTB_S pin pulls down the FAULTB pin
together that turns off the no fault condition channel
but keep 4mA sourcing on fault channel for recovery
detection. In multiple LEDs per string application, set
the detection threshold voltage VDT into below voltage
range:
( N 1) VF _ max VDT N VF _ min
(6)
Where, N is the number of LEDs in the string. VF_max
and VF_min are the maximum and minimum forward
voltage of a single LED.
Figure 35
OUTx Pins Short Operation
In the event the LED channel is open circuited, the
OUTx pin voltage will go up close to VCC. If VCC to
OUTx drop voltage remains below the threshold VOCD
for tFD, the fault channel will change to source a 4mA
current for recovery detection and the another channel
will turn off. The FAULTB pin will be pulled low to
indicate the fault condition. The state will recover after
the open condition is removed.
If the ISETx pin is either short or open, the FAULTB pin
will pull low to assert the fault and the both channels
will turn off. The state will recover after the fault
condition is removed.
FAULTB PARALLEL INTERCONNECTION
Figure 34
STx Pins Operation
The detection threshold voltage VDT is calculated by
the following Equation (7):
VDT VST
RST 1 RST 2
RST 2
THERMAL ROLLBACK OF OUTPUT CURRENT
(7)
If single LED short detection is unused, the unused
STx pin should be tied to its corresponding OUTx pin.
OUTPUT STATE
DIAGNOSTIC
DETECTION
AND
FAULT
IS32LT3126 offers a fault diagnostic function. Output
short to GND/VCC, LED string open/short, ISET pins
short/open and over temperature shutdown will trigger
this function.
An output short to GND or VCC is detected as a fault if
the OUTx pin voltage drops below the short detect
voltage threshold VSCD or VCC to OUTx drop voltage is
lower than VOCD and remains below the threshold for
tFD. Then the fault channel will change to source a 4mA
current for recovery detection and the other channel
will turn off. The FAULTB pin will be pulled low to
indicate the fault condition. This state will recover after
the fault condition is removed.
Lumissil Microsystems – www.lumissil.com
Rev. A, 05/08/2018
For LED lighting systems which require the complete
lighting system be shut down when a fault is detected,
the FAULTB pin can be used in a parallel connection
with multiple IS32LT3126 devices as shown in Figure
2. A detected fault output by one device will pull low
the FAULTB pins of the other parallel connected
devices and simultaneously turn them off. This
satisfies the “One-Fail-All-Fail” operating requirement.
To protect the IC from damage due to high power
dissipation, the temperature of the die is monitored.
When the temperature of the die is below the thermal
rollback start threshold of 145°C (Typ.), the dual output
current maximum is the value set by the selection of
RISETx. When the die temperature is between the
thermal rollback start threshold 145°C (Typ.) and the
over temperature shutdown threshold 165°C (Typ.),
the output current decreases linearly from the
maximum value. During the rollback, the FAULTB pin
will not assert this as a fault.
The rollback is related to RISET value:
I OUT _ RO I OUT
K (TJ 145C )
RISET
(8)
Where 145°C ≤TJ≤165°C and K=49.
14
IS32LT3126
Any attempt to enable one or both of the channels
back to the source condition before the IC cooled to
TJTRO
Output current linearly
decreases following TJ
High
High
TJTSD
Off
Low
High
TJ
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