DataSheet.jp

IS31LT3948 の電気的特性と機能

IS31LT3948のメーカーはISSIです、この部品の機能は「PFM MODE BOOST LED DRIVER」です。


製品の詳細 ( Datasheet PDF )

部品番号 IS31LT3948
部品説明 PFM MODE BOOST LED DRIVER
メーカ ISSI
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IS31LT3948 Datasheet, IS31LT3948 PDF,ピン配置, 機能
IS31LT3948
PFM MODE BOOST LED DRIVER WITH THE EXTERNAL NMOS
GENERAL DESCRIPTION
FEATURES
OCTOBER 2011
The IS31LT3948 is a PFM step-up DC-DC converter
designed for driving the white LED arrays for large
size LCD panel backlighting applications. It can
deliver stable constant output current from a few
milliamps up to 2A, programmed via an external
resistor.
The IS31LT3948 utilizes a control scheme in which
the output is automatically adjusted to the optimum
output voltage for the system, maximizing the
efficiency. Furthermore, the control scheme is
inherently stable removing the need to provide
additional loop compensation.
The device features external PWM dimming, which
allows the flexible control of the back-lighting
luminance.
The IS31LT3948 has a wide input voltage range from
5V to 100V (Note). An integrated OVP circuit protects
the chip and the system even under no-load
conditions.
Note: The IS31LT3948 has an internal 5V shunt regulator
connected to the VCC pin. A dropping resistor must be
connected between the VCC pin and VIN to limit current flow.
VIN voltages above 100V are allowed but care must be taken to
ensure that the output voltage remains greater than VIN, and that
the NMOS voltage rating is sufficiently large.
Wide input voltage range: 5V-100V
Constant Current Output limited only by external
component selection (Note)
No loop compensation required
Internal over-voltage protection
Internal over-temperature protection
Operating temperature range -40°C to 85°C
SOP-8 package
Note: The maximum output current is determined by Vout/Vin ratio
as well as the external components. If output current and Vout/Vin
ratio is high, high current components of inductor and NMOS are
needed.
APPLICATIONS
TV Monitor Backlighting,
Notebook
Automotive
Street Lamp
LED Lighting
http://www.DataSheet4U.net/
TYPICAL OPERATING CIRCUIT
VIN(5~100V)
L1
D1
LED(+)
R1
C1
R2
C2
VCC
TOFF
ADJ
GND
GATE
CS
OVP
FB
M1
C3
R3
R4
R5
LED(-)
Rfb
Figure 1 Typical Operating Circuit
Copyright © 2011 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
Rev. A, 8/31/2011
1
datasheet pdf - http://www.DataSheet4U.net/

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IS31LT3948 pdf, ピン配列
IS31LT3948
ABSOLUTE MAXIMUM RATINGS
Parameter
Value
VCC to GND
-0.3V to 6V
CS, ADJ,GATE,TOFF,OVP,FB
-0.3V to 6V
VCC Max. Input Current(note)
Junction Temperature Range
Storage Temperature Range
10mA
-40oC to +150oC
-65oC to +150oC
ESD Human Model
3500V
Notes:
1. Exceeding VCC maximum input current may cause the pin not to clamp at 5V.
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
(Unless otherwise specified, Vin=10V, Rin=10K, ADJ floating, Tamb=25 oC)
Symbol
Parameter
Conditions
VINDC Input voltage
VCC
UVLO
VCC clamp voltage
Undervoltage threshold
Δ UVLO Undervoltage threshold hysteresis
Supply voltage
connected to VCC via a
appropriate resistor
(Note)
Rin=10KOhm
VCC rising
http://www.DataSheet4U.net/
Min
5
4.3
2.0
spec
Typ
Max
Unit
100 V
5 5.6 V
2.7 3.0 V
300 mV
ISS
VCSTH
Quiescent supply current
Quiescent supply current when
VCC undervoltage
Peak current sense threshold
VCC=5V
VCC=2.5V
ADJ=5V
250
50
215 240
400 uA
75 uA
265 mV
TBLANK Peak current sense blank interval VCS=VCSTH+50mV
500 ns
TOFF Fixed turn-off interval
Rext=250KΩ
10 us
Peak current control low threshold
VADJ
Peak current control high threshold
0.5 V
2.4 V
TSD
TSD-HYS
Thermal shutdown threshold
Thermal shutdown hysteresis
125 oC
20 oC
VfbTH Feedback voltage threshold
0.29
0.3
0.31
V
VOVP-TH Overvoltage input threshold
0.9 1
1.1 V
Note:
VIN is the input voltage. When VIN • 5V, connect input voltage directly to Vcc. When VIN > 5V, input voltage should be connected to Vcc pin via
an appropriately valued resistor.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 8/31/2011
3
datasheet pdf - http://www.DataSheet4U.net/


3Pages


IS31LT3948 電子部品, 半導体
IS31LT3948
APPLICATION INFORMATION
Internal 5V Regulator
The IS31LT3948 includes an internal shunt regulator of
5V (typ.) connected to the VCC pin. When the input
voltage is higher than 5V, connect VCC to VIN using an
appropriately valued, current limiting resistor. The
regulator maintains a 5V power supply for the internal
NMOS switch gate driver and the internal control
circuitry. In applications where the input voltage is 5V,
connect the input voltage directly to VCC. When VCC is
connected directly to VIN, VIN may not exceed 5V.
Bypass the VCC pin using a low ESR capacitor
(recommended 10µF ceramic capacitor) to provide a
high frequency path to GND.
The current required by IS31LT3948 is 0.25mA
(typical) plus the switching current of the external
switch. The switching frequency of the external NMOS
affects the amount of current required, as does the
NMOS’s gate charge requirement (found on the NMOS
data sheet).
IIN 0.25mA + QG × fS
(1)
Where fS is the switching frequency and QG is the
external NMOS gate charge.
Under Voltage Lockout
IS31LT3948 features an under voltage lockout
threshold of 2.7V (typical) with a hysteresis of 300mV.
The chip is disabled when VCC is lower than 2.4V and
enabled when VCC exceeds 2.7V.
Step-up Converter
IS31LT3948’s step-up converter uses a peak current
mode topology wherein the CS pin voltage determines
the peak current in the inductor of the converter and
hence the duty cycle of the GATE switching waveform.
The basic loop uses a pulse from an internal oscillator
to set an RS flip-flop and turn on the external power
NMOS. After the blanking time, the inductor current is
sensed during the GATE on period by a sense resistor,
RCS, in the source of the external power NMOS. The
current through the NMOS and inductor increases until
the voltage across the sense resistor reaches the CS
threshold, at this time, the NMOS is turned off. Once
the NMOS is turned off, the inductor reverses polarity,
providing the voltage boost, and the current of inductor
will decrease until the FB pin voltage drops below an
internal reference voltage and the NMOS is then
turned on again. This operation repeats in each cycle.
Note: In the case where the FB pin voltage does not
exceed the FB reference voltage of 0.3V, such as at
the start-up, the NMOS will remain off for the
programmed minimum TOFF time, then the NMOS is
switched on again.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 8/31/2011
LED Current Control
IS31LT3948 regulates the LED current by sensing the
voltage across an external sense resistor in series with
the LEDs. The voltage is sensed via the FB pin where
the internal feedback reference voltage is 0.3V. The
LED current can be set according to the following
equation easily.
I out
=
0.3
R fb
(2)
In order to have an accurate LED current, precision
resistors are required (1% is recommended).
Setting the Over Voltage Protection
The open string protection is achieved through the over
voltage protection (OVP). In some cases, an LED
string failure will set the feedback voltage to always
zero. If this happens, the chip will keep boosting the
output voltage higher and higher again. If the output
voltage reaches the programmed OVP threshold, the
protection mechanism will be triggered and stops the
switching action. To make sure that the circuit
functions properly, the OVP setting resistor divider
must be set with an appropriate value. The
recommended VOVP point is about 1.25 times or 5V
(choose the larger one) higher than the output voltage
for normal operation.
http://www.DataSheet4U.net/
VOVP
= VOVPTH
×
R4 + R5
R5
(3)
Where, VOVP-TH is 1V, and VOVP is the output voltage
OVP level.
Dimming Control
There are two methods for dimming.
1) External NMOS PWM dimming:
LED(-)
FB
ISS3N13L9T438948
GND
ADJ
M2
Rfb
PWM
Figure 10
When the PWM input is high (VH>2.4V), M2 is on and
IS31LT3948 operates normally to regulate the output
current. When PWM is low (VL<0.5V), M2 is off and
IS31LT3948 is shutdown. Using a fixed frequency
PWM signal and changing the duty cycle adjusts the
average output current. The recommended 5V PWM
frequency is between 200Hz and 1KHz. M2 is
recommended to use AP2306.
6
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6 Page



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部品番号部品説明メーカ
IS31LT3948

PFM MODE BOOST LED DRIVER

ISSI
ISSI


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