IS31LT3948-GRLS2-TR ISSI, IS31LT3948-GRLS2-TR Datasheet

IS31LT3948-GRLS2-TR

Manufacturer Part Number

IS31LT3948-GRLS2-TR

Description

LED Lighting Drivers PFM Mode Boost LED Drvr

Manufacturer

ISSI

Datasheet

1.IS31LT3948-GRLS2-TR.pdf (14 pages)

Specifications of IS31LT3948-GRLS2-TR

Input Voltage

5 V to 100 V

Maximum Supply Current

400 uA

Maximum Operating Temperature

+ 85 C

Mounting Style

SMD/SMT

Package / Case

SOP-8

Factory Pack Quantity

2500

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b.) the user assume all such risks; and

IS31LT3948

PFM Mode Boost LED Driver With the External NMOS

General Description

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.

Typical Operating Circuit

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;

c.) potential liability of Integrated Silicon Solution, Inc is adequately protected under the circumstances

Integrated Silicon Solution, Inc. – www.issi.com

Rev.B, 12/24/2012

Figure 1 Typical Operating Circuit

Features



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



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

TV Monitor Backlighting,

Notebook

Automotive

Street Lamp

LED Lighting

December 2012

Related parts for IS31LT3948-GRLS2-TR

IS31LT3948-GRLS2-TR Summary of contents

Page 1

... 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 ...

Page 2

... FB 8 OVP Ordering Information Order Part No. Package IS31LT3948-GRLS2-TR SOP-8, Lead-free Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 Top View Positive power supply input pin. Internally clamped at 5V (typical). Off time setting pin. An external resistor connected to this PIN forms an RC discharge path to generate a constant minimum off time of the NMOS Enable and input peak current control pin ...

Page 3

... IS31LT3948 Absolute Maximum Ratings VCC to GND CS, ADJ,GATE,TOFF,OVP,FB VCC Max. Input Current(note) Junction Temperature Range Storage Temperature Range ESD Human Model Note: Exceeding VCC maximum input current may cause the pin not to clamp at 5V. 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 ...

Page 4

... IS31LT3948 Typical Performance Characteristics 400 380 360 340 320 , Vout=40V,Rfb=0.825 Rcs=0.12 L=100uH,Cout=220uF(Low ESR) 300 Vin(V) Figure 2. Vin & Iout 400 380 360 340 320 Vin=12V,Rfb=0.825,Rcs=0.12 ESR) L=100uH,Cout=220uF(Low 300 Vout(V Figure 4. Vout & Iout ...

Page 5

... IS31LT3948 800 770 740 710 680 Vout=48V,Rfb=0.392,Rcs=0.1 Vint=24V,Rfb=0.392,Rcs=0.1  ESR) ESR) L=100uH,Cout=220uF(Low L=100uH,Cout=220uF(Low 650 Vout(V) Figure 8. Vout & Iout Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 100 Vin=24V,Rfb=0.392 ...

Page 6

... When the PWM input is high (V IS31LT3948 operates normally to regulate the output current. When PWM is low logic (V 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 recommended to use AP2306 ...

Page 7

... CSTH CSTH Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 Input Capacitor The input capacitor of the IS31LT3948 will supply the transient input current of the power inductor. Value of 100μF or higher is recommended to prevent excessive input voltage ripple. Setting T IS31LT3948 operates in a pulsed frequency modulation mode ...

Page 8

... Proportionally lower ripple can be achieved with higher capacitor values. Schottky Rectifier The external diode for the IS31LT3948 must be a Schottky diode, with low forward voltage drop and fast switching speed. The diode’s average current rating must exceed the application’s average output current. ...

Page 9

... IS31LT3948 VIN(5~100V PWM Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 L1 M1 VCC GATE TOFF CS ADJ OVP R3 GND FB Figure.12 External NMOS PWM dimming Figure.13 RC filter PWM dimming D1 LED(+) R4 LED(-) Rfb 9 ...

Page 10

... IS31LT3948 Example Input: Vin = 12~24V Output: Iout = 350mA, Vout≈30~40V (9~12LEDs, Vf=3.3V) To calculate the worst case parameter, use the minimum input voltage, the maximum output voltage, and maximum output current. So choose: Vin = 12V, Iout = 350mA, Vout≈40V (12LEDs, Vf=3.3V and C1&C2 Assume Iin = 2.5mA  ...

Page 11

... IS31LT3948 6. R4 set OVP Set V = Vout+5V = 45V OVP     OVP OVP  Choose R5=10kΩ, then R4 = 470kΩ. 7. NMOS M1 and diode D1 I1 >I (NMOS) peak IN （） V1 >V (NMOS) OVP Integrated Silicon Solution, Inc. – www.issi.com Rev ...

Page 12

... IS31LT3948 Classification Reflow Profiles Preheat & Soak Temperature min (Tsmin) Temperature max (Tsmax) Time (Tsmin to Tsmax) (ts) Average ramp-up rate (Tsmax to Tp) Liquidous temperature (TL) Time at liquidous (tL) Peak package body temperature (Tp)* Time (tp)** within 5°C of the specified classification temperature (Tc) Average ramp-down rate (Tp to Tsmax) Time 25° ...

Page 13

... IS31LT3948 Tape and Reel Information Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 13 ...

Page 14

... IS31LT3948 Package Information Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 12/24/2012 14 ...

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