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STMicroelectronics Electronic Components Datasheet

L5981 Datasheet

1A step-down switching regulator

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L5981 pdf
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L5981
1A step-down switching regulator
Features
„ 1A DC output current
„ 2.9V to 18V input voltage
„ Output voltage adjustable from 0.6V
„ 250kHz switching frequency, programmable
up to 1MHz
„ Internal soft-start and inhibit
„ Low dropout operation: 100% duty cycle
„ Voltage feed-forward
„ Zero load current operation
„ Over current and thermal protection
„ VQFN3x3-8L package
Applications
„ Consumer:
STB, DVD, DVD recorder, car audio, LCD TV
and monitors
„ Industrial:
Chargers, car battery, PLD, PLA, FPGA
„ Networking: XDSL, modems, DC-DC modules
„ Computer:
Optical storage, hard disk drive, printers,
audio/graphic cards
Figure 1. Application circuit
VFQFPN8 3x3
Description
The L5981 is step down switching regulator with
1.5A current limited embedded power MOSFET,
so it is able to deliver in excess of 1A DC current
to the load depending on the application
condition.
The input voltage can range from 2.9V to 18V,
while the output voltage can be set starting from
0.6V to VIN. Having a minimum input voltage of
2.9V, the device is suitable also for 3.3V bus.
Requiring a minimum set of external components,
the device includes an internal 250kHz switching
frequency oscillator that can be externally
adjusted up to 1MHz.
The QFN package with exposed pad allows
reducing the RthJA down to approximately
60°C/W.
L5981
October 2007
Rev 2
1/37
www.st.com
37


STMicroelectronics Electronic Components Datasheet

L5981 Datasheet

1A step-down switching regulator

No Preview Available !

L5981 pdf
www.DataSChoeent4teUn.ctosm
Contents
L5981
1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1 Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3 Error amplifier and compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4 Over-current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.5 Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.6 Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5 Application informations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.4.1 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.4.2 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2/37


Part Number L5981
Description 1A step-down switching regulator
Maker STMicroelectronics
Total Page 30 Pages
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