ISSI IS32LT3175N Single channel linear led driver with fade in/out and pwm dimming Datasheet

IS32LT3175N/P
SINGLE CHANNEL LINEAR LED DRIVER WITH FADE IN/OUT AND PWM DIMMING
July 2016
GENERAL DESCRIPTION
FEATURES
The IS32LT3175 is a single channel linear
programmable current regulator capable of up to
150mA. It integrates a debounce and latch circuit on
the channel enable pin (EN) to facilitate the use of a
low cost momentary contact switch. The PWM pin can
be interfaced to a logic level “courtesy light” signal to
directly drive the LED channel. The IS32LT3175P
accepts a positive polarity PWM signal while the
IS32LT3175N accepts a negative polarity PWM signal.


The device operates as a stand-alone LED driver
configurable with external resistors; no microcontroller
is required. A single external resistor programs the
current level, while two separate resistors
independently program the fade in and fade out ramp
rate for the channel.
The device integrates a 63 steps fade in and fade out
algorithm (Gamma correction) which causes the output
LED current to gradually ramp up to the full source
value after the EN pin is pulsed. The same controller
causes the LED current to gradually ramp down to
zero if the EN pin is pulsed while the output channel is
ON. The fade ramp can be interrupted mid-cycle
before completion of the ramp cycle. The EN pin will
accept either a momentary contact switch or logic level
signal pulsed low.
The IS32LT3175 is targeted at the automotive market
with end applications to include map and dome lighting
as well as exterior accent lighting. For 12V automotive
applications the low dropout driver can support 1 to 3
LEDs (VF = 3.2V) per channel. It is offered in a small
thermally enhanced SOP-8-EP package.






Operating voltage 5V to 42V
Single channel current source
- Programmable current via a single external
resistor
- Configurable from 20mA to 150mA
Momentary contact button EN input
- Input is debounced and latched
- Higher priority than PWM input
- Gamma corrected Fade In/Out algorithm
- Pull down resistors set independent fade IN and
OUT ramp time
PWM input pin driven by external PWM source
- PWM directly drives the current source
- IS32LT3175P – Positive polarity
- IS32LT3175N – Negative polarity
Fault Protection:
- OUT pin shorted to GND
- ISET pin shorted to GND
- Over temperature
SOP-8-EP package
Automotive Grade:
- IS32LT3175P – AEC-Q100
- IS32LT3175N – AEC-Q100
Operating temperature range from -40°C ~ +125°C
APPLICATIONS

Automotive Interior:
- Map/Dome light
- Puddle lamp in doors
- Glove box
- Vanity mirror
TYPICAL APPLICATION CIRCUIT
Figure 1
Typical Application Circuit
Note: The resistor RPWM is a fixed value. Please don’t change it. CPWM is optional. Add it for robust electromagnetic susceptibility.
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IS32LT3175N/P
PIN CONFIGURATION
Package
Pin Configuration (Top view)
SOP-8-EP
PIN DESCRIPTION
No.
Pin
Description
1
EN
Internally debounced input pin for control of LED current. A
negative going pulse on this pin will toggle the state of the OUT
current. The pin condition is constantly monitored after the
debounce time period.
2
ISET
Output current setting for channel. Connect a resistor between
this pin and GND to set the maximum output current.
3
TSET_UP
Timing control for the Fade In feature. Connect a resistor
between this pin and GND to set the Fade In time. Connect this
pin directly to ground to disable the fade function for instant ON.
4
TSET_DN
Timing control for the Fade Out feature. Connect a resistor
between this pin and GND to set the Fade Out time. Connect
this pin directly to ground to disable the fade function for instant
OFF.
5
GND
Ground pin for the device.
6
OUT
Output current source channel.
7
VCC
Power supply input pin. A capacitor on this pin will help maintain
EN latch status during low voltage conditions.
PWM
PWM (or BCM) signal via a 10kΩ to drive OUT pin. Pin
condition is ignored if EN pin has latched and activated OUT
pin. IS32LT3175P positive polarity, IS32LT3175N negative
polarity.
Thermal Pad
Connect to GND.
8
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IS32LT3175N/P
ORDERING INFORMATION
Automotive Range: -40°C to +125°C
Order Part No.
Package
QTY/Reel
IS32LT3175P-GRLA3-TR
IS32LT3175N-GRLA3-TR
SOP-8-EP, Lead-free
2500
Copyright © 2016 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
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IS32LT3175N/P
ABSOLUTE MAXIMUM RATINGS
VCC, OUT, PWM
EN, ISET, TSET_UP, TSET_DN
Ambient operating temperature, TA=TJ
Maximum continuous junction temperature, TJ(MAX)
Storage temperature range, TSTG
Maximum power dissipation, PDMAX
ESD (HBM)
ESD (CDM)
-0.3V ~ +45V
-0.3V ~ +7.0V
-40°C ~ +125°C
150°C
-55°C ~ +150°C
1.96W
±2kV
±750V
Note:
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.
THERMAL CHARACTERISTICS
Characteristic
Test Conditions
Value
Package Thermal Resistance
(Junction to Ambient), θJA
Package Thermal Resistance
(Junction to Pad), θJP
On 4-layer PCB based on JEDEC standard
at 1W, TA=25°C
50.98°C/W
2.24°C/W
ELECTRICAL CHARACTERISTICS
TJ = -40°C ~ +125°C, VCC=12V, refer to each condition description. Typical values are at TJ = 25°C.
Symbol
Parameter
VCC
Supply voltage range
VDO
Minimum dropout
voltage
Condition
tON
Quiescent supply
current
Startup time
IOUT_LIM Output limit current
IOUT
Output current
(Note 3)
EOUT
Absolute current
accuracy (Note 3)
Typ.
5
Max. Unit
42
V
VCC –VOUT, IOUT= -150mA (Note 1)
900
mV
VCC –VOUT, IOUT= -100mA (Note 2)
700
mV
1
mA
PWM pin floating. EN disables the output.
ICC
Min.
0.1
RISET=15kΩ, EN enable the output, PWM floating,
OUT floating
2.3
3.8
mA
VCC=4.2V, EN enable the output. VPWM=4V for
IS32LT3175P and VPWM=GND for IS32LT3175N.
0.25
0.6
mA
400
μs
VCC> 6V to IOUT<-5mA (Note 4)
VCC –VOUT =1V, OUT sourcing current,
ISET pin connected to GND.
-240
-205
-160
mA
RISET = 15kΩ, VCC –VOUT =1V,-40°C<TJ<+125°C
-105
-100
-95
mA
-50mA≤IOUT≤-20mA, VCC –VOUT =1V,
-40°C< TJ <+125°C
-8
8
%
-150mA≤IOUT<-50mA, VCC –VOUT =1V,
-40°C< TJ <125°C
-6
6
%
gLINE
Output current line
regulation
IOUT = -50mA, 6V<VCC<18V, VOUT = VCC -2V
(Note 4)
-0.2
0.2
mA/V
gLOAD
Output current load
regulation
2.5V< VOUT <VCC-2.0V,IOUT = -50mA (Note 4)
-0.2
0.2
mA/V
Current slew time
Current rise/fall between 0%~100%, VTSET = 0V
70
100
μs
PWM current latency
Delay time between PWM rising edge to 10% of
IOUT
10
17
μs
tSL
tTD_ON
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4
IS32LT3175N/P
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
UVLO
Parameter
Release from under voltage
lock out VCC voltage
Condition
Min.
VCC rising release from UVLO
Into under voltage lock out VCC
VCC falling into UVLO
voltage
4.1
Typ.
Max.
Unit
4.6
4.8
V
4.5
4.7
V
Logic Input TSET_UP, TSET_DN
VTSET Voltage reference
TACC
Fade timing accuracy
1
*Neglecting the RTSET Tolerance*
RTSET_UP=100kΩ, TJ = 25°C
-5
V
5
%
0.8
V
Logic Input PWM – Active High (IS32LT3175P)
VIL
Input low voltage
VIH
Input high voltage
VIN_HY Input hysteresis
IPD
Internal pull-down current
2
V
(Note 4)
150
350
VPWM=12V
15
28
mV
46
μA
0.8
V
Logic Input PWM – Active Low (IS32LT3175N)
VIL
Input low voltage
VIH
Input high voltage
VIN_HY Input hysteresis
IPU
Internal pull-up current
2
V
(Note 4)
150
350
VPWM=GND
20
38
mV
58
μA
0.8
V
Logic Input EN
VIL
Input low voltage
VIH
Input high voltage
VIN_HY Input hysteresis
2
(Note 4)
150
V
350
mV
50
kΩ
RPU
Internal pull-up resistor
(Note 4)
IPU
Internal pull-up current
VEN=0
55
75
95
μA
tSW
EN input debounce time
EN pin must not change state within
this time to be interpreted as a switch
press or release
25
37
50
ms
Measured at OUT
1.2
1.8
V
Protection
VSCD
Short detect voltage
VSCD_HY Short detect voltage hysteresis Measured at OUT
220
mV
tFD
Fault detect persistence time
(Note 4)
5
ms
TRO
Thermal roll off threshold
(Note 4)
145
°C
TSD
Thermal shutdown threshold
Temperature increasing (Note 4)
175
°C
THY
Over temperature hysteresis
Recovery = TSHT – TJ_HY (Note 4)
30
°C
Note 1: IOUT output current in case of VCC-Vout=VDO called IOUT_VDO. IOUT output current in case of VCC-VOUT=2V called IOUT_VDO2V, VDO accuracy is
computed as |IOUT_VDO-IOUT_VDO2V|/IOUT_VDO2V<5%.
Note 2: IOUT output current in case of VCC-VOUT=VDO called IOUT_VDO. IOUT output current in case of VCC-VOUT=1V called IOUT_VDO1V, VDO accuracy is
computed as |IOUT_VDO-IOUT_VDO1V|/IOUT_VDO1V<5%.
Note 3: Output current accuracy is not intended to be guaranteed at output voltages less than 1.8V.
Note 4: Guaranteed by design.
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IS32LT3175N/P
TYPICAL PERFORMANCE CHARACTERISTICS
3
200
RTSET = 100kΩ
RISET = 15kΩ
No Load
2
Output Current (mA)
Supply Current (mA)
2.5
RTSET = 100kΩ
VDO = 1V
Operating Mode
1.5
Shutdown Mode
1
150
RISET = 15kΩ
100
50
RISET = 75kΩ
0.5
0
5
10
15
20
25
30
35
40
0
5
45
RISET = 10kΩ
10
15
Supply Voltage (V)
30
Output Current (mA)
100
50
0
45
VCC = 12V
RISET = 15kΩ
RTSET = 0Ω
PWM Frequency is 50Hz,100Hz,300Hz
80
60
40
20
10
50
100
150
0
200
0
20
40
Figure 4
60
80
100
Duty Cycle (%)
RISET (kΩ)
Output Current vs. RISET
Figure 5
Output Current vs. PWM Duty Cycle
2000
2000
VCC = 12V
RISET = 20kΩ
RISET = 20kΩ
RTSET = 600kΩ
RTSET = 600kΩ
1500
1500
1000
Fade Time (ms)
Fade Time (ms)
40
100
VCC = 12V
RTSET = 100kΩ
VDO = 1V
TJ = 25°C
150
RTSET = 300kΩ
500
0
35
Output Current vs. Supply Voltage
Figure 3
200
Output Current (mA)
25
Supply Voltage (V)
Supply Current vs. Supply Voltage
Figure 2
20
10
15
20
RTSET = 300kΩ
500
RTSET = 100kΩ
5
1000
25
30
35
40
45
RTSET = 100kΩ
0
-40 -25
-10
Supply Voltage (V)
Figure 6
Fade Time vs. Supply Voltage
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5
20
35
50
65
80
95
110 125
Temperature (°C)
Figure 7
Fade Time vs. Temperature
6
IS32LT3175N/P
200
3.5
VCC = 12V
RTSET = 0Ω
VDO = 1V
Output Current (mA)
Supply Current (mA)
3
VCC = 12V
RTSET = 0Ω
RISET = 15kΩ
No Load
2.5
Operating Mode
2
1.5
Shutdown Mode
1
RISET = 10kΩ
150
RISET = 15kΩ
100
RISET = 30kΩ
50
RISET = 75kΩ
0.5
0
-40
-25
-10
5
20
35
50
65
80
95
110 125
0
-40
-5
30
Supply Current vs. Temperature
Figure 9
PWM On Delay Time
RTSET = 0Ω
RISET = 15kΩ
135
175
Output Current vs. Temperature
PWM Off Delay Time
RTSET = 0Ω
RISET = 15kΩ
VV
PWM
EN
2V/Div
VVPWM
EN
2V/Div
IOUT
50mA/Div
IOUT
50mA/Div
Time (10µs/Div)
Time (10µs/Div)
Figure 10
100
Temperature (°C)
Temperature (°C)
Figure 8
65
PWM On Delay Time (For IS32LT3175P Only)
Figure 11
PWM On Delay Time (For IS32LT3175P Only)
RTSET = 0Ω
RTSET = 0Ω
IOUT
20mA/Div
IOUT
20mA/Div
Time (20µs/Div)
Time (20µs/Div)
Figure 12
Instant on
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Figure 13
Instant Off
7
IS32LT3175N/P
Fade In
RTSET = 100kΩ
Fade Out
RTSET = 100kΩ
IOUT
20mA/Div
IOUT
20mA/Div
VEN
5V/Div
VEN
5V/Div
Time (100ms/Div)
Figure 14
Time (100ms/Div)
VEN vs. IOUT
Figure 15
Fade In
RTSET = 510kΩ
VEN vs. IOUT
Fade Out
RTSET = 510kΩ
IOUT
50mA/Div
IOUT
50mA/Div
VEN
5V/Div
VEN
5V/Div
Time (400ms/Div)
Figure 16
Time (400ms/Div)
VEN vs. IOUT
Figure 17
Fade In
RTSET = 510kΩ
Enable Twice
VEN vs. IOUT
Fade Out
RTSET = 510kΩ
Enable Twice
IOUT
50mA/Div
IOUT
50mA/Div
VEN
2V/Div
VEN
2V/Div
Time (400ms/Div)
Figure 18
Time (400ms/Div)
VEN vs. IOUT
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Figure 19
VEN vs. IOUT
8
IS32LT3175N/P
200
Output Current (mA)
RTSET = 0Ω
TJ = 25°C
RISET = 10kΩ
160
RISET = 15kΩ
120
80
RISET = 30kΩ
40
0
0
2000
4000
6000
8000
10000
Headroom Voltage (mV)
Figure 20
Output Current vs. Headroom Voltage
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IS32LT3175N/P
FUNCTIONAL BLOCK DIAGRAM
Note: IS32LT3175P does not invert the PWM input.
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IS32LT3175N/P
APPLICATION INFORMATION
The IS32LT3175 is a single channel linear current
driver optimized to drive an automotive interior LED
map light, or other interior lamp which is frequently
toggled between the In and Out condition. The device
integrates a debounce input circuit to enable use of a
low cost momentary contact switch for controlling
In/Out an external LED. In addition, a programmable
fade ramp timing function provides flexibility in setting
different Fade In and Fade Out ramp duration periods.
The fade ramp cycle can be interrupted mid-cycle
before the ramp has completed, Figure 21.
mA in the time period as programmed by the resistor
(RTSET_DN) attached to the TSET_DN pin.
ENx
Debounce
Time
Debounce
Time
OUTx (On Condition)
Fade In
OUTx (Off Condition)
Fade Out
t
Fade In
Figure 22
Figure 21
Fade Ramp Interrupted Mid-cycle
The regulated LED current (up to 150mA) is set by a
single reference resistor (RISET).
OUTPUT CURRENT SETTING
A single programming resistor (RISET) controls the
maximum output current for output channel
simultaneously. The programming resistor may be
computed using the following Equation (1):
RISET
1500

I SET
(1)
(10kΩ≤RISET≤75kΩ)
The device is protected from an output overcurrent
condition caused by an accidental short circuit of the
ISET pin, by internally limiting the maximum current in
the event of an ISET short circuit to 205mA (Typ.).
EN PIN OPERATION
The EN pin has in integrated pull-up source so that no
external components are required to provide the input
high level to the pin.
The output channel powers up in the ‘OFF’ condition.
Toggling the EN pin from high to low for a period of
time that exceeds the debounce time will cause the
output to be toggled and latched from the OFF
condition to the current source condition. When this
happens, the output current gradually ramps up from
zero mA to the programmed value (set by RISET) over
the time set by the resistor (RTSET_UP) attached to the
TSET_UP pin. Conversely, if it is already in the source
condition, and the EN pin is toggled low, then the
output current will begin to ramp down towards zero
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EN Debounced
Debounce – Output control is provided by a
debounced switch input, providing an ON/OFF toggle
action for various switch or button characteristics. An
internal debounce circuit will condition the EN input
signal so a single press of the mechanical switch
doesn’t appear like multiple presses. The EN input is
debounced by typically 37ms.
Note: The debounce time applies to both falling and
rising edges of the EN signal.
FADE IN AND FADE OUT DIMMING
The LED fade function can be accomplished in one of
two methods; 1) by applying a PWM control signal to
the PWM pin, or 2) when the EN pin is pulled low.
PWM Dimming – The PWM pin can be driven by an
external PWM signal source to accomplish LED
dimming. The integrated gamma correction and fade
IN/OUT ramp functions are disabled when actively
driving the PWM pin. The PWM pin input is ignored if
the LED channel was previously active due to the EN
pin. The EN pin will override the PWM function; it can
be used to toggle the LED channel from its previous
state even though the PWM pin is active.
The recommended PWM signal frequency range is
50Hz-300Hz. The duty cycle can be 0-100%. The
output current of the PWM dimming is given by:
I OUT 
1500
 DPWM
RISET
Where, DPWM is the duty cycle of the PWM. Please
refer to Figure 10 and 11 for the delay time of PWM
edge to current change edge. Figure 24 and 25 show
the PWM polarity difference of IS32LT3175P and
IS32LT3175N.
11
IS32LT3175N/P
EN Dimming –The LED output current will gradually
ramp up from zero to the final value as programmed by
the resistor (RISET) connected to the ISET pin. The time
period over which the ramping happens is determined
by the resistor (RTSET_UP) connected to the TSET_UP
pin for Fade In time and by resistor (RTSET_DN)
connected to TSET_DN pin for Fade Out time. The
output current will ramp up (or down) in 63 steps, with
integrated gamma correction for an extremely visual
linear lumen output of the LED. The ramp time can be
interrupted mid-cycle each time the EN pin is pulled
low.
the EN latch status as long as the VCC pin voltage
remains above 3.8V. An external capacitor (Figure 23)
is necessary to help maintain the VCC pin
voltage >3.8V and to supply current to the device
status latch circuitry. However, should the voltage drop
below 3.8V, the internal latch will be reset to the power
on default status (LED initial off state).
The current source will be turned ON when the input
voltage is re-applied and the VCC pin rises above 4.6V
(Typ.).
The EN function has priority over the PWM function; if
the LED has been turned on due to the EN function
then the PWM dimming pin input is ignored.
UNDERVOLTAGE LOCKOUT
IS32LT3175N/P integrates an undervoltage lockout
function to prevent mis-operation of the device during
low input voltage conditions.
Figure 23
Capacitor For Latch Status
Should the VCC pin voltage fall below 4.5V (Typ.), the
device will turn OFF the current source and maintain
PWM Duty Cycle
Ramp Up
PWM High
PWM Duty Cycle
Ramp Down
LED Full On
PWM Low
PWM Low
LED Off
LED Fade Out
LED Fade In
PWM Signal Input (Positive Polarity – IS32LT3175P)
Figure 24
PWM High
LED Off
PWM Duty Cycle
Ramp Up
PWM Duty Cycle
Ramp Down
PWM High
LED Off
LED Off
PWM Low
LED Fade In
Figure 25
LED Full On
PWM Signal Input (Negative Polarity – IS32LT3175N)
SETTING THE FADE TIME
The fade time is set by two external programming
resistors; RTSET_UP and RTSET_DN. The RTSET_UP
connected to the TSET_UP pin configures the fade
ramp ON time while the RTSET_DN connected to the
TSET_DN pin configures the fade ramp out time. The
fade time (In or Out) is programmable by Equation (2):
t  RTSET  2.5s
LED Fade Out
(2)
Note: In order to get the optimized effect, the
recommended fading time is between 1.5s (RTSET=
600kΩ) and 0.25s (RTSET= 100kΩ).
If either the TSET_UP or TSET_DN pin is tied directly
to GND, the corresponding fade function is canceled
and the ramp time is about 70µs, or ‘instant on’.
However, the debounce feature of the EN pin is not
disabled.
For example, RTSET=100kΩ, Fade In/Out time is about
0.25s.
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IS32LT3175N/P
2500
900
800
LED Current Duty
2000
Fade Time (ms)
1000
VCC = 12V
RISET = 15kΩ
TJ = 25°C
1500
1000
500
700
600
500
400
300
200
100
0
100
200
400
600
800
1000
0
0
5
10
15
20
RTSET (kΩ)
30
35
40
45
50
55
60 62
Gamma Steps
Fade Time vs. RTSET
Figure 26
25
Figure 27
Gamma Correction(63 Steps)
GAMMA CORRECTION
FAULT DETECTION
In order to perform a better visual LED breathing effect
we recommend using a gamma corrected value to set
the LED intensity. This results in a reduced number of
steps for the LED intensity setting, but causes the
change in intensity to appear more linear to the human
eye.
An output shorted to GND fault is detected if the output
voltage on a channel drops below the low voltage
threshold VSCD and remains below the threshold for tFD.
The channel (OUT) with the short condition will reduce
its output current to 20% of ISET. When the short
condition is removed, the output current will recover to
original value.
Gamma correction, also known as gamma
compression or encoding, is used to encode linear
luminance to match the non-linear characteristics of
display. Gamma correction will vary the step size of the
current such that the fading of the light appears linear
to the human eye. Even though there may be 1000
linear steps for the fading algorithm, when gamma
corrected, the actual number of steps could be as low
as 63.
Table 1
63 Gamma Steps Correction
C(0)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
0
2
4
6
8
10
12
16
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
20
24
28
32
36
42
48
54
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
60
66
72
80
88
96
104
112
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
120
130
140
150
160
170
180
194
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
208
222
236
250
264
282
300
318
C(40)
C(41)
C(42)
C(43)
C(44)
C(45)
C(46)
C(47)
336
354
372
394
416
438
460
482
C(48)
C(49)
C(50)
C(51)
C(52)
C(53)
C(54)
C(55)
504
534
564
594
624
654
684
722
C(56)
C(57)
C(58)
C(59)
C(60)
C(61)
C(62)
760
798
836
874
914
956
1000
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
When the ISET pin is shorted to GND and output
current is larger than limit value, about 205mA, the
output current will be clamped. Once the short fault
condition is removed, the output current will recover to
its original value.
OVERTEMPERATURE PROTECTION
The device features an integrated thermal rollback
feature which will reduce the output current in a linear
fashion if the silicon temperature exceeds 145°C
(typical). In the event that the die temperature
continues to increase, the device will enter thermal
shutdown if the temperature exceeds 175°C.
THERMAL ROLLOFF
The output current will be equal to the set value as
long as the die temperature of the IC remains below
145°C (Typical). If the die temperature exceeds this
threshold, the output current of the device will begin to
reduce at a rate of 3%/°C.
The roll off slope is related to ISET value. When
ISET=20mA, the roll off slope is about 3.7%. When
ISET=150mA, the roll off slope is about 2.2%.
THERMAL SHUTDOWN
In the event that the die temperature exceeds 175°C,
the output channel will go to the ‘OFF’ state. At this
point, the IC presumably begins to cool off. Any
attempt to toggle the channel back to the source
condition before the IC cooled to < 145°C will be
blocked and the IC will not be allowed to restart.
13
IS32LT3175N/P
THERMAL CONSIDERATIONS
The package thermal resistance, θJA, determines the
amount of heat that can pass from the silicon die to the
surrounding ambient environment. The θJA is a
measure of the temperature rise created by power
dissipation and is usually measured in degree Celsius
per watt (°C/W). The junction temperature, TJ, can be
calculated by the rise of the silicon temperature, ∆T,
the power dissipation, PD, and the package thermal
resistance, θJA, as in Equation (3):
PD  VCC  I CC  (VCC  VLED )  I OUT
The thermal resistance is achieved by mounting the
IS32LT3175N/P on a standard FR4 double-sided
printed circuit board (PCB) with a copper area of a few
square inches on each side of the board under the
IS32LT3175N/P. Multiple thermal vias, as shown in
Figure 29, help to conduct the heat from the exposed
pad of the IS32LT3175N/P to the copper on each side
of the board. The thermal resistance can be reduced
by using a metal substrate or by adding a heatsink or
thicker copper plane.
(3)
and,
TJ  TA  T  TA  PD   JA
(4)
Where ICC is the IC quiescent current, VCC is the supply
voltage, VLED is the voltage across VCC to OUT and TA
is the ambient temperature.
When operating the chip at high ambient temperatures,
or when driving maximum load current, care must be
taken to avoid exceeding the package power
dissipation limits. The maximum power dissipation can
be calculated using the following Equation (5):
PD ( MAX ) 
(5)
 JA
Vehicle electronics can be affected by electromagnetic
interference (EMI) caused by ‘stray’’ magnetic and
electric fields from automotive inductive load switching.
Running throughout the vehicle are wiring harnesses
which behave as ‘‘hidden antennas’’ and pickup these
harmonic frequencies.
So,
125C  25C
 1.96W
50.98C / W
Figure 28, shows the power derating of the
IS32LT3175 on a JEDEC board (in accordance with
JESD 51-5 and JESD 51-7) standing in still air.
2.5
SOP-8-EP
Power Dissipation (W)
Board Via Layout For Thermal Dissipation
EMI AT THE CABLE AND INTERCONNECT LEVEL
125C  25C
PD ( MAX ) 
Figure 29
2
Because the IS32LT3175 is usually connected with a
long wire to the vehicle’s central computer, it could be
susceptible to EMI transients. For example, a coupled
EMI transient on the wiring harness connected to the
IS32LT3175’s PWM pin 8 can be passed through and
cause a slight LED flicker.
1
To avoid this, an RC low-pass filter can be
implemented to attenuate high frequency signals at the
PWM pin. The low-pass filter will allow only low
frequency signals from 0Hz to its cut-off frequency (ƒc)
to pass while attenuating frequencies above this cut-off
frequency.
0.5
The formula to calculate the cut-off frequency of an RC
filter is:
1.5
0
-40
fC 
-25
-10
5
20
35
50
65
80
95
110 125
Temperature (°C)
Figure 28
Dissipation Curve
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
1
2  RPWM  C PWM
(6)
As shown in Figure 30, typical values for RPWM=10kΩ
and CPWM=3.3nF. For the IS32LT3175 the value of
RPWM is fixed at 10kΩ (must always be installed) while
CPWM is optional and its value can vary depending on
the vehicle’s EMI environment.
14
IS32LT3175N/P
8
PWM
50Hz~300Hz
RPWM
10k
PWM
CPWM
3.3nF
IS32LT3175N/P
Figure 30
fC 
RC filter for PWM EMI
1
 4.7 kHz
2  10k  3.3nF
Frequencies above 4.7kHz will be attenuated while
frequencies below 4.7kHz will pass through without
attenuation.
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
Figure 31 Low-pass filter gain-magnitude frequency response
15
IS32LT3175N/P
CLASSIFICATION REFLOW PROFILES
Profile Feature
Pb-Free Assembly
Preheat & Soak
Temperature min (Tsmin)
Temperature max (Tsmax)
Time (Tsmin to Tsmax) (ts)
150°C
200°C
60-120 seconds
Average ramp-up rate (Tsmax to Tp)
3°C/second max.
Liquidous temperature (TL)
Time at liquidous (tL)
217°C
60-150 seconds
Peak package body temperature (Tp)*
Max 260°C
Time (tp)** within 5°C of the specified
classification temperature (Tc)
Max 30 seconds
Average ramp-down rate (Tp to Tsmax)
6°C/second max.
Time 25°C to peak temperature
8 minutes max.
Figure 30
Classification Profile
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
16
IS32LT3175N/P
PACKAGE INFORMATION
SOP-8-EP
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
17
IS32LT3175N/P
RECOMMENDED LAND PATTERN
1.27
1.75
2.41
3.3
5.6
0.65
Note:
1. Land pattern complies to IPC-7351.
2. All dimensions in MM.
3. This document (including dimensions, notes & specs) is a recommendation based on typical circuit board manufacturing parameters. Since
land pattern design depends on many factors unknown (eg. User’s board manufacturing specs), user must determine suitability for use.
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
18
IS32LT3175N/P
REVISION HISTORY
Revision
0A
0B
0C
A
Detail Information
Initial release
1. Update typical application circuit
2. Add UVLO description
3. Update Figure 24 and 25
1. Update functional block
2. Update EC table
3. Update Gamma Correction section
4. Update Figure 10 and 11
5. Update Automotive Grade
1. Update Typical Application Circuit with RC on PWM pin
2. Add description of PWM pin EMI considering
3. Update Automotive Grade
Integrated Silicon Solution, Inc. – www.issi.com
Rev.A, 07/19/2016
Date
2016.05.04
2016.03.31
2016.05.27
2016.07.19
19