IS31LT3554

IS31LT3554
BOOST TYPE LED DRIVER WITH 4-CHANNEL CURRENT SOURCE
August 2015
GENERAL DESCRIPTION
FEATURES
The IS31LT3554 is a LED driver based on a highly
efficient boost controller operating over a wide input
voltage range of 4.5V to 33V.
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The IS31LT3554 contains four regulated current
sources with 1.5% (Typ.) current matching between
strings for a uniform LED brightness. Each current
source can be programmed via an external resistor to
drive from 20mA to 180mA. A fast slew rate current
source allows high frequency and narrow pulse width
dimming signals to achieve a very high contrast ratio.
The device operating frequency can be adjusted from
0.1MHz to 1MHz.
The IS31LT3554 has safety protection features to
prevent damage during fault conditions. Protection
features include an internal soft-start circuit to prevent
a high inrush current during startup, open/short LED
protection to automatically disable a faulty current
source, over temperature protection (OTP),
cycle-by-cycle current limit, under voltage lockout
(UVLO), programmable OVP, VOUT short / Schottky
diode open protection and Schottky Diode
short-circuit protection.
Input voltage range: 4.5V to 33V
4-Channel LED current sinks, 180mA per string
LED current adjustable from 20mA to 180mA
String-to-string current matching accuracy: 1.5%
Adjustable operating frequency: 100kHz to 1MHz
External PWM dimming
High contrast ratio
Less than 3µA shutdown current
Programmable soft-start
Built-in protection features
- OCP, OTP, UVLO
- Open/short LED protection
- Programmable OVP
- Schottky Diode/inductor short-circuit protection
APPLICATIONS
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LCD Monitor/TV
LED lighting
The IS31LT3554 is available in a thermally enhanced
eTSSOP-16 package.
TYPICAL APPLICATION CIRCUIT
Figure 1
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Rev. A, 08/18/2015
Typical Application Circuit
1
IS31LT3554
PIN CONFIGURATION
Package
Pin Configuration (Top View)
eTSSOP-16
PIN DESCRIPTION
No.
Pin
Description
1
RT
A resistor value to ground sets the switching frequency from 100kHz to 1MHz.
2
EN
Enable Input. The IC is Enabled when this pin is above 2.4V. The IC is Disabled
and in Shutdown mode when this pin is below 0.5V. In shutdown mode only a
minimal 3µA current is consumed.
3
CS
Current Sense Input from the switching converter. A sense resistor from the
source of the external N-MOSFET to GND sets the switching current limit.
4
OUT
Switching N-MOSFET Gate Drive Output. This pin outputs a high voltage
(5V/VCC-0.5V) to drive an external switching N-MOSFET.
5
VCC
5V linear regulator output. Bypass this pin to GND with a ceramic capacitor as
close as possible to the pin.
6
VIN
Supply input (4.5V to 33V). Bypass VIN to GND with a capacitor (typical 10µF)
to keep the DC input voltage constant.
7
STATUS
LED operation status will output logic low if a fault is detected.
8
COMP
Soft-start and control loop compensation.
9
DIM
PWM signal input for LED dimming. If dimming is not implemented, connect it
to VCC pin 5.
10,11
CH1,CH2
LED current sink 1 and 2 (up to 180mA). If unused leave the pin open
unconnected.
12
GND
Ground. Connect all grounds at a single point.
13,14
CH3,CH4
LED current sink 3 and 4 (up to 180mA). If unused leave the pin open
unconnected.
15
ISET
LED Current Adjust Input. Connect a resistor RISET between ISET pin and GND
to set the reference current through each LED string.
OVP
Over Voltage Protection pin. Connect a resistor-divider from the switching
converter output to this pin. The OVP comparator reference is internally set to
2.0V. Above 2.0V triggers OVP and shuts down switch power; switch resumes
normal operation when the pin voltage drops below hysteresis voltage.
Thermal Pad
Connect to GND.
16
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2
IS31LT3554
ORDERING INFORMATION
Industrial Range: -40°C to +125°C
Order Part No.
Package
QTY
IS31LT3554-ZLS4-TR
IS31LT3554-ZLS4
eTSSOP-16, Lead-free
2500/Reel
96/Tube
Copyright © 2015 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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Rev. A, 08/18/2015
3
IS31LT3554
ABSOLUTE MAXIMUM RATINGS
Input voltage, VIN
CH1 to CH4 voltage, VCH
GND pin voltage, VGND
Voltage in other pins, VPIN
Thermal resistance, θJA
Thermal simulation @25°C ambient temperature, still air convection,
2s2p boards according to JESD51.
Operating junction temperature, TJ
Lead Temperature(Soldering, 10s), TLEAD
Storage temperature range, TSTG
Operating ambient temperature range, TA =TJ
ESD(HBM)
ESD(CDM)
-0.3V ~ +42V
-0.3V ~ +55V
-0.3V ~ +0.3V
-0.3V ~ +7.0V
39.9°C/W
150°C
260°C
-65°C ~ +150°C
-40°C ~ +125°C
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.
RECOMMENDED OPERATING CONDITIONS
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
VIN
Input voltage
4.5
33
V
fOSC
Switch frequency
0.1
1
MHz
ILEDX
LED channel current
20
180
mA
fPWM
PWM dimming frequency
(Note 1)
0.1
20
kHz
Operating ambient temperature
TA = TJ
-40
125
°C
TA
ELECTRICAL CHARACTERISTICS
VIN =12V, VEN=5V, typical values are at TA = 25°C, unless otherwise noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
33
V
3
5
mA
Input Supply
VIN
Input voltage
ICC
Quiescent current
No switching
ISD
Shutdown current
VEN = VDIM = 0V
0.1
3
μA
UVLO
VIN Rising
3.8
4.2
V
VUVLO
4.5
VUVLO_HYS UVLO hysteresis
0.2
V
5
V
VIN-0.1
V
VCC Section
VCC
VCC voltage
VIN ≥ 5.5V
VIN < 5.5V, ILOAD = 10mA
tRISING
Out pin rising time
1nF load (Note 1)
30
50
ns
tFALLING
Out pin falling time
1nF load (Note 1)
30
50
ns
Load Regulation
VIN = 12V, ILOAD = 0mA ~ 30mA
5
10
mV/mA
Line Regulation
VIN = 6.5V ~ 12V, ILOAD = 1mA
3
10
mV/V
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IS31LT3554
ELECTRICAL CHARACTERISTICS (CONTINUED)
VIN =12V, VEN=5V, typical values are at TA = 25°C, unless otherwise noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
High Frequency Oscillator
tON-TIME
Minimum on-time
f = 500kHz (Note 1)
200
fOSC
Switch frequency (10% variation)
RT = 100kΩ
440
520
DMAX
Maximum duty cycle
f = 500kHz
88
90
ns
570
kHz
%
Enable Logic And Dimming Logic
VEN_H
EN high voltage
VEN_L
EN low voltage
VDIM_H
VDIM_L
tPWM_MIN
2.4
0.5
2.5
PWM logic for external dimming
PWM dimming minimum pulse width
V
V
0.3
(Note 1)
V
3/fOSC
V
µs
Power Switch Drive
VLIMIT
Current limit threshold voltage
480
560
640
mV
VLIMIT2
D/I short threshold voltage
720
800
930
mV
80
100
150
ns
tLEB
Current sense LEB time
(Note 1)
Compensation And Soft Start (COMP Pin)
GEA
Error amplifier trans-conductance
2300
µA/V
IO_H
Sourcing current
VCOMP=0.5V
55
120
200
µA
IO_L
Sinking current
VCOMP=2V
60
120
200
µA
VOUT rising
1.8
2.0
2.2
V
Over-Voltage Protection
VOVP
OVP threshold voltage
VOVP_HYS
OVP hysteresis
200
250
330
mV
VOVP_SD
Shutdown under abnormal condition
3.0
3.2
3.6
V
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IS31LT3554
ELECTRICAL CHARACTERISTICS (CONTINUED)
VIN =12V, VEN=5V, typical values are at TA = 25°C, unless otherwise noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
1.5
3
%
100
108
mA
230
400
mV
50
V
0.1
1
µA
7.3
8.0
V
Current Source
ICH_MATCH
LED current matching between
each string
ILED = 100mA (Note 2)
ILED
Regulation current per channel
RSET = 12kΩ
Minimum LED regulation voltage
ILED = 100mA
VLED_REG
VLEDX
ILED_LEAK
VLED_S
92
LED channel voltage
CH1 to CH4 leakage current
VEN = 0V, VLED = 50V
LED Short protection threshold
6.6
Over-Temperature Protection
TOTSD
Thermal shutdown temperature
(Note 1)
160
ºC
THYS
Thermal shutdown recovery
(Note 1)
140
ºC
Note 1: Guaranteed by design and characterization, not production tested.
Note 2:
I ST _ MATCH 
I MAX  I MIN
 100 % .
2  I AVG
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IS31LT3554
FUNCTIONAL BLOCK DIAGRAM
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7
IS31LT3554
APPLICATION INFORMATION
DESCRIPTION
The IS31LT3554 is a highly integrated HBLED driver.
The device operates from an input voltage up to 33V.
Advanced features include detection and string
disconnect for open LED strings, partial or fully shorted
strings and unused strings. Overvoltage protection
clamps the converter output voltage to the
programmed OVP threshold in the event of an open
LED string condition. The STATUS pin outputs string
open or short circuit conditions and over voltage or
over temperature conditions.
ENABLE
When the EN pin connected to a logic-low the
IS31LT3554 will completely shut down, reducing its
current consumption to less than 3µA. The device is
enabled when the logic threshold at EN exceeds 2.4V
and it is disabled when it is lower than 0.5V.
Where, D MIN 
1
t D  t SU
and t PWM 
t PWM
f PWM
tD is the propagation delay from the time PWM logic
signal goes high to the time that the LED driver begins
to increase the output current. tSU is the slew up time
needed for the output current from zero to the set level.
Base on the equations, the lower PWM dimming
frequency, fPWM, the higher contrast ratio, as these
fixed delays consume a smaller portion of the dimming
period, tPWM. The lower limit for fPWM is approximately
100Hz, below which the eye no longer blends the
pulses into a perceived continuous light. The upper
limit is determined by the minimum contrast ratio that is
required.
Time (2µs/Div)
LED CURRENT SETTING
The maximum LED current per channel can be
adjusted up to 180mA via ISET pin. When ≥ 180mA
current is needed for an application, two or more
channels can be paralleled to provide larger drive
current. Connect resistor RSET between ISET pin and
GND to set the reference current ISET. The LED current
can be expressed as below Equation (1):
I LED [ mA ] 
1200
R SET [ k ]
(1)
The current regulator of the IS31LT3554 has a fast
response so that it can allow a very high contrast ratio.
PWM
2V/Div
ILED
200mA/Div
tSU
tD
Figure 2
PWM vs. LED Current
DIMMING CONTROL
FREQUENCY SELECTION
A PWM signal applied to the DIM pin will adjust the
LED current to all enabled channels. During the “high
level” period of the PWM signal, the LED is turned ON
and 100% of the current flows, while during the “low
level” period the LED is turned OFF and almost no
current flows. This ON/OFF operation generates an
average current flow that will set the LED brightness
between 1%×ICHX_MAX to 100% × ICHX_MAX. A 100Hz (or
higher) PWM signal frequency can be applied to PWM
pin.
The IS31LT3554’s switching frequency can be
adjusted between 100kHz to 1MHz by using an
external resistor RT, placed between RT pin and GND.
A low frequency operation can help to reduce switch
loss for a higher efficiency while a high frequency
operation will minimize the external component size.
The approximate operating frequency can be
expressed as below Equation (3):
CONTRAST RATIO
The PWM dimming contrast ratio (CR) of the system
depends on the PWM frequency, the value of external
components, input/output voltage and so on.
The CR definition can be showed by following
Equation (2):
CR 
1
D MIN
(2)
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f OSC [ MHz ] 
52
RT [ k ]
(3)
STATUS OUTPUT
The STATUS output provides a warning of extreme
operating or fault conditions. After initial power up, the
STATUS pin will output a logic low (normally high) if
any of the following conditions exists:
(1) Any string is open
(2) LED short circuit protection
(3) Shut down under abnormal condition
8
IS31LT3554
(4) Over voltage protection
(5) Over temperature protection
(6) Schottky Diode short protection
(7) VOUT Short/Open Schottky Diode protection
PROTECTION FEATURES
The IS31LT3554 is designed with integrated safety
features for a reliable and stable operation in the
normal operating range. In the event of more than one
fault condition occurring, the higher priority condition
will take precedence.
SOFT START
The internal soft start circuit prevents a high inrush
current during startup.
OVER VOLTAGE PROTECTION
The IS31LT3554 integrates an OVP circuit to prevent
system damage should the output voltage become
excessive. To maintain a safe output level, the
integrated OVP circuit continuously monitors the
voltage output level. The OVP pin is connected to the
center tap of voltage-divider (ROV1 and ROV2)
connected between high voltage output and GND. If
the voltage on OVP pin exceeds 2.0V the IS31LT3554
stops switching, which causes the output voltage to
drop. When the OVP pin voltage drops below the
threshold the device begins oscillating once again,
which causes the output voltage to rise. This OVP
hysteresis is 250mV (VOVP_HYS). The formula to
calculate VOVP can be expressed as below Equation
(4):
VOVP 
ROV 1  ROV 2  2.0V
ROV 2
(4)
VOVP = OVP voltage
VOVP_HYS = OVP hysteresis voltage
OVER CURRENT PROTECTION
The IS31LT3554 integrates an OCP circuit. The CS pin
is connected to the external voltage-sense resistor
(RCS) that is placed between the drain of MOS and
GND. If the voltage on CS pin exceeds 0.56V (VLIMIT), it
is turned OFF immediately and will not turn ON until
the next cycle begins.
SCHOTTKY DIODE/INDUCTOR SHORT CIRCUIT
PROTECTION
The IS31LT3554 features a Schottky diode/inductor
short-circuit protection circuit. When CS pin voltage
exceeds 0.8V (VLIMIT2) for more than 16 switching
clocks, the IC will latch. The voltage of CS is monitored
after a short delay of Leading Edge Blanking signal.
approximate 2.0V threshold. The IC will automatically
ignore the open string whose corresponding pin
voltage is less than 100mV and the remaining string
will continue operation. If all the strings are open and
the voltage at OVP reaches a threshold of 2.0V, the
MOSFET drive GATE will turn off and IC will shut down
and latch.
LED SHORT CIRCUIT PROTECTION
The IS31LT3554 integrates an LED short-circuit
protection circuit. If the voltage at any of the two
channel pins exceeds a threshold of approximately
7.3V (VLED_S) during normal operation, the
corresponding string is turned off and is latched off. To
reset the latch and start operation, the VIN and/or EN
must be toggled OFF/ON. The priority of the LED short
detecting logic is lower than the open LED and OVP
logic. The LED short circuit detection logic is triggered
when VLED_MIN is <0.1V under dimming on mode. It is
disabled when an LED open occurs or when the output
voltage resumes to the regulated output level.
VOUT SHORT / OPEN SCHOTTKY DIODE
PROTECTION
The IS31LT3554 monitors the OVP pin, if the OVP pin
voltage is less than 0.1V, MOSFET drive output will
turn off. This protects the converter if the output
schottky diode is open or VOUT is shorted to ground.
UNDER VOLTAGE LOCKOUT
The IS31LT3554 provides an under voltage lockout
circuit with built in hysteresis to prevent an undefined
status during startup. The UVLO circuit shuts down the
device when VCC drops below 3.6V (typical) and will
turn when VCC rises above 3.8V. The UVLO circuit has
a 200mV hysteresis (VUVLO_HYS), which means the
device will start up when VCC rises above 3.8V.
OVER TEMPERATURE PROTECTION
The thermal overload protection prevents excessive
power dissipation from overheating and damaging the
IS31LT3554. If the junction temperature exceeds
approximately 160ºC (TOTSD), the IC will shut down to
allow it to cool down. The device will begin a soft-start
process when the junction temperature (TJ) of the die
falls below approximately 140ºC (THYS).
SHUT DOWN UNDER ABNORMAL CONDITION
The IS31LT3554 integrates a shutdown under
abnormal condition protection circuit. When the OVP
pin voltage exceeds 3.2V (VOVP_SD), the IC will latch.
The EN pin must then be toggled to restart the IC. This
feature can be used for any other protection to shut
down the IC.
LED OPEN CIRCUIT PROTECTION
The IS31LT3554 integrates an LED open-circuit
protection circuit. When any LED string is open, VOUT
will boost up until the voltage at OVP pin reaches an
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IS31LT3554
Step 3a: Calculate the maximum required LED output
voltage, VOUT.
APPLICATION INFORMATION
DESIGN EXAMPLE FOR IS31LT3554
This section describes a component calculation
method for selecting component values when
designing with the IS31LT3554 (Figure 1).
For the purposes of this example, the following
assumptions are given as application requirements:
(5)
The ILED = 120mA, so the RSET should be:

1200
I LED [ mA ]
1200
 10 k
120
Choose a 10kΩ resistor for RSET.
Step 2: Calculate the frequency setting resistor RT
using Equation (6):
f OSC [ MHz ] 
52
RT [ k ]
(6)
ROV 1  ROV 2  2.0
ROV 2
(4)
Pick a standard resistor value of 56kΩ for ROV2 then
calculate for ROV1 = 1.0MΩ.
Note: Multiplier 1.2x is added for design margin to
cover noise and output ripple voltage.
Step 4: Choose the input filter capacitor. The input
capacitor (CIN) filters the current peaks drawn from the
input supply and reduces noise injection into the
IS31LT3554. A 22μF/63V electrolytic capacitor is
recommended for most applications.
Step 5: Choose the output capacitors. The output
capacitors provide filtering for both the boost converter
and for the PWM dimming function. The biggest
factors that contribute to the size of the output
capacitor are: PWM dimming frequency and PWM duty
cycle. Another major contributor is leakage current, ILK;
the reverse current of the switching diode. In this
design the PWM dimming frequency is to be 100Hz
and the minimum duty cycle is 0.1%. Typically, the
voltage variation on the output, VCOUT, during PWM
dimming must be less than 250mV, to minimize any
audible hum. The output capacitance is calculated
using Equation (9):
C OUT  I LK 
Therefore, for an fOSC = 1MHz, RT is calculated as:
RT [ k ] 
Step 3b: Use VOVP Equation (4) to calculate ROV1 and
ROV2.
Therefore, ROV 1  18 .2  ROV 2
Step 1: Calculate the LED current setting resistor RSET
using Equation (5):
R SET [ k ] 
(8)
 1.2  VOUT  1.2  32V  38 .4V
Once the initial operating parameters have been
identified, the next step is to sequentially calculate the
individual parameters in an ordered manner starting
with Step 1 and continuing step by step until the final
Step 5.
1200
R SET [ k ]
 10  3 .2  32V
VOVP [V ] 
VIN = 12V
LED Loading = 10×4
LED current per channel, ILED = 120mA
LED VF1 = 3.2V at 120mA
fOSC = 1MHz
Efficiency, η = 90%
I LED [ mA ] 
VOUT  ( Number SERIES LED )  V F 1
52
f OSC [ MHz ]
1  DMIN
f PWM  VCOUT
1  0.001
 1000 
 39 .96 F
100  0.25
(9)
Where ILK= 1mA.
52

 52 k
1
Choose a standard resistor value of 51kΩ for RT.
Note: A high fOSC operating frequency will result in a
smaller PWM duty cycle enabling high contrast
dimming results.
Because capacitors tend to degrade when subjected to
high voltages; a capacitance value greater than
39.96μF should be selected.
Two 22μF 63V capacitors connected in parallel are a
good choice to fulfill this requirement.
Step 3: Calculate OVP resistors ROV1 and ROV2, using
Equation (7):
VOVP [V ] 
ROV 1  ROV 2  2.0
ROV 2
(7)
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IS31LT3554
Step 6: Calculate duty cycle DON using Equation (10):
DON
 V IN
V
 OUT
VOUT
32  12

 62 .5%
32
 1 .42  0 .5  0 .75  1 .795 A
DON
f OSC
Step 6a: Calculate the average input current IIN(Avg),
using Equation (12):
V
 I LED  4
 OUT
V IN  
(12)
32  0.12  4

 1 .42 A
12  0 .9
Equation (13) is used to calculate the maximum ripple
current IRIPPLE(MAX):
I RIPPLE ( MAX )  2  I IN ( Avg )
(13)
 2  1 .42  2 .84 A
Step 6b: Calculate the minimum inductor value, L1.
using Equation (14):
LCCM ( MIN ) 
V IN  t ON
I RIPPLE ( MAX )
(14)
12  0.625

 2.64 H
2.84
The selected value for L1 should be higher than the
LCCM(MIN). A lower inductance for L1 will result in a
narrower PWM duty cycle for high contrast dimming.
The trade off for a low inductance is higher output
current ripple. Therefore choose a 10µH inductor for
L1.
Step 6c: Determining the peak input current IPEAK,
calculated as follows:
First calculate the ripple current IRIPPLE using Equation
(15):
I RIPPLE 
t ON  V IN
L1
0 .625  12

 0.75 A
10
RCS [ ]  0.8 
0.54
I PEAK [ A]
(17)
0.54
 0 .8 
 0.24 
1.795
Choose a 0.235Ω resistor for RCS.
(11)
0.625

 0.625 s
1
I IN ( Avg )
(16)
Step 6d: The peak current protect resistor RCS is
shown in Equation (17):
(10)
The turn on time tON is calculated using Equation (11)
below:
t ON 
I PEAK  I IN ( Avg )  0 .5  I RIPPLE
(15)
Then calculate the inductor peak current using
Equation (16):
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Generally a constant term, 0.8x, is added when
calculating the RCS value. A lower RCS value will result
in a higher IPEAK to prevent over current protection
errors.
Step 7: The boost converter requires a diode to carry
the inductor current during the MOSFET off time.
Schottky diodes are recommended due to their fast
recovery time and low forward voltage. D1 should be
rated to handle the maximum output voltage (plus
switching node ringing) and the peak switch current.
The conduction loss of the diode is calculated by:
PDIODE  I RMS _ OFF  V F
I RMS _ OFF 
2
2
V IN  2 I L 

  I IN 
VOUT 
12 
(18)
Where VF is the forward voltage of the Schottky diode.
Step 8: The IS31LT3554 integrates a soft start and
control loop compensation in COMP Pin. The soft start
feature allows the boost converter to gradually reach
its initial steady state output voltage, thereby reducing
startup stresses and current surges. The startup time
is controlled by an internal 130μA (ICS) current source
and the external compensation circuit composed of CC
and RC. When powering on, after the VIN UVLO
threshold is satisfied, the internal 130μA current
source charges the external capacitor CC. The COMP
pin voltage will ramp up slowly and limit the inrush
current during startup. The soft start time is determined
by the Equation (19):
t SS 
VCOMP  C C
I CS
(19)
Where VCOMP is the voltage of COMP pin and ICS is the
internal source current. Typically, a value of RC=1kΩ
and CC=0.22µF is sufficient for operating at 500kHz.
Low-ESR Surface-Mount Ceramic Capacitors (MLCCs)
are recommended. For most applications, ceramic
capacitors with X7R temperature characteristics are
preferred. These capacitors have tight capacitance
tolerance (as good as ±10%) and hold their value over
temperature (X7R: ±15% over -55°C to 125°C).
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IS31LT3554
Step 9: The IS31LT3554 includes an internal low
dropout linear regulator with the output pin VCC. This
pin is used to power the internal PWM controller,
control logic and MOSFET driver. The regulator
generates a 5V supply when VIN≥5.5V. When VIN is
less than 5.5V, connect VCC directly to VIN.
The VCC pin should be decoupled with a 2.2μF
ceramic capacitor placed as close to the pin as
possible. This capacitor keeps VCC voltage steady
when the system operates at a high frequency. X7R
type ceramic capacitors should be used for decoupling
due to their good thermal stability.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 08/18/2015
12
IS31LT3554
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
Figure 3
8 minutes max.
Classification Profile
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 08/18/2015
13
IS31LT3554
PACKAGE INFORMATION
eTSSOP-16
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 08/18/2015
14
IS31LT3554
RECOMMENDED LAND PATTERN
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, 08/18/2015
15
IS31LT3554
REVISION HISTORY
Revision
A
Detail Information
Initial release
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 08/18/2015
Date
2015.08.18
16