IS31LT3948 Datasheet, PDF (1/14 Pages) Integrated Silicon Solution, Inc – PFM MODE BOOST LED DRIVER WITH THE EXTERNAL NMOS

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
TYPICAL OPERATING CIRCUIT
VIN(5~100V)
L1
D1
LED(+)
R1
C1
R2
C2
VCC
TOFF
ADJ
GND
GATE
CS
OVP
FB
R4
M1
C3
R3
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
1
Rev. A, 8/31/2011