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LM34914 Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit
December 20, 2007
LM34914 Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit
General Description
The LM34914 Step-Down Switching Regulator features all the functions needed to implement a low cost, efficient, buck bias regulator capable of supplying at least 1.25A to the load. To reduce excessive switch current due to the possibility of a saturating inductor the valley current limit threshold changes with input and output voltages, and the on-time is reduced when current limit is detected. This buck regulator contains a 44V N-Channel Buck Switch, and is available in the thermally enhanced 3 mm x 3 mm LLP-10 package. The feedback regulation scheme requires no loop compensation, results in fast load transient response, and simplifies circuit implementation. The operating frequency remains constant with line and load variations due to the inverse relationship between the input voltage and the on-time. The valley current limit results in a smooth transition from constant voltage to constant current mode when current limit is detected, reducing the frequency and output voltage, without the use of foldback. Additional features include: VCC under-voltage lock-out, thermal shutdown, gate drive under-voltage lock-out, and maximum duty cycle limit.
Features
■ Input Voltage Range: 8V to 40V ■ Integrated N-Channel buck switch
■ Valley current limit varies with VIN and VOUT to reduce
excessive inductor current
■ On-time is reduced when in current limit ■ Integrated start-up regulator ■ No loop compensation required ■ Ultra-Fast transient response ■ Maximum switching frequency: 1.3 MHz ■ Operating frequency remains nearly constant with load
current and input voltage variations
■ Programmable soft-start ■ Precision internal reference ■ Adjustable output voltage ■ Thermal shutdown
Typical Applications
■ High Efficiency Point-Of-Load (POL) Regulator ■ Non-Isolated Buck Regulator ■ Secondary High Voltage Post Regulator
Package
■ LLP-10 (3 mm x 3mm) ■ Exposed Thermal Pad For Improved Heat Dissipation
Basic Step Down Regulator
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LM34914
Connection Diagram
Ordering Information
Order Number Package Type
LM34914 SD LM34914 SDX
LLP-10 (3x3) LLP-10 (3x3)
20197302
10-Lead LLP
NSC Package Drawing SDA10A SDA10A
Junction Temperature Range
Supplied As
−40°C to + 125°C −40°C to + 125°C
1000 Units on Tape and Reel 3500 Units on Tape and Reel
Pin Descriptions
Pin Number 1
Name SW
Description Switching Node
2 BST Boost pin for bootstrap capacitor
3
ISEN
Current sense
4
SGND
Sense Ground
5
RTN
Circuit Ground
6 FB Feedback input from the regulated output
7 SS Softstart
8 RON/SD On-time control and shutdown
9 VCC Output from the startup regulator
10 VIN Input supply voltage EP Exposed Pad
Application Information
Internally connected to the buck switch source. Co.