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Partno	Mfg	Dc	Qty	Available	Descript
L7981	ST	N/a	120	avai	3 A step-down switching regulator
L7981A	ST	N/a	4	avai	3 A step-down switching regulator
L7981ATR	ST	N/a	12	avai	3 A step-down switching regulator

L7981 ,3 A step-down switching regulatorFunctional description . . . . . . . 85.1 Oscillator and synchronization . . 95.2 Soft-sta ..
L7981A ,3 A step-down switching regulatorFeatures 3 A DC output currentDescription 4.5 V to 28 V input voltageThe L7981 device is a step-d ..
L7981ATR ,3 A step-down switching regulatorApplicationsThe QFN and the HSOP packages with exposed pad allow reducing the R down to 60°C/W and ..
L7985 ,2A step-down switching regulatorFeaturesDescription 2 A DC output currentThe L7985/A is a step-down switching regulator  4.5 V to ..
L7985A ,2A step-down switching regulatorFunctional description . . . . . . . 85.1 Oscillator and synchronization . . 95.2 Soft-sta ..
L7986 ,3A step-down switching regulatorFunctional description . . . . . . . 85.1 Oscillator and synchronization . . 95.2 Soft-sta ..
LC6529N ,4-Bit Microcomputer for Small-Scale Control ApplicationsOrdering number : EN*5117CMOS LSILC6529N, LC6529F, LC6529L4-Bit Microcomputer for Small-Scale Contr ..
LC6538D ,SINGLE-CHIP 4-BIT MICROCOMPUTER FOR LARGE-SCALE CONTROL-ORIENTED APPLICATIONSFeaturesT . 78 instructions ,. On-chip 8192-byte ROM, 448x4-bit RAM (64x4 bits of the 448x4-bit RAM ..
LC6543C ,CMOS LSI SINGLE-CHIP 4-BIT MICROCOMPUTERS FOR SMALL-SCALE CONTROL-ORIENTED APPLICATIONSFeatures1) CMOS technology for Iow-power operation (with instruction-gon2) ROM/RAML66543C/H ROM; 2K ..
LC6543F ,CMOS LSI SINGLE-CHIP 4-BIT MICROCOMPUTER FOR SMALL-SCALE CONTROL-ORIENTED APPLICATIONSFeatures1) CMOS technology for a low-power operation (with instruction-controlled standby function) ..
LC6543F ,CMOS LSI SINGLE-CHIP 4-BIT MICROCOMPUTER FOR SMALL-SCALE CONTROL-ORIENTED APPLICATIONSOrdering number: EN 4364AOvervigwSINGLE-CHH‘3 4-Bl'i' MICROCOMPUTER FORMN543N/F/1.,, 6546N/F/L .CMO ..
LC6543H ,CMOS LSI SINGLE-CHIP 4-BIT MICROCOMPUTERS FOR SMALL-SCALE CONTROL-ORIENTED APPLICATIONSFeatures1) CMOS technology for Iow-power operation (with instruction-gon2) ROM/RAML66543C/H ROM; 2K ..

L7981-L7981A-L7981ATR
3 A step-down switching regulator
May 2014 DocID15182 Rev 5 1/42
L7981
3 A step-down switching regulator
Datasheet - production data
Features 3 A DC output current 4.5 V to 28 V input voltage Output voltage adjustable from 0.6 V 250 kHz switching frequency, programmable
up to 1 MHz Internal soft-start and enable Low dropout operation: 100% duty cycle Voltage feed-forward Zero load current operation Overcurrent and thermal protection VFQFPN 3 x 3 - 8L and HSOP8 package
Applications Consumer: STB, DVD, DVD recorder, car audio, LCD
TV and monitors Industrial: PLD, PLA, FPGA, chargers Networking: XDSL, modems, DC-DC modules Computer: Optical storage, hard disk drive, printers,
audio/graphic cards Suitable for LED driving
Description
The L7981 device is a step-down switching
regulator with a 3.7 A (minimum) current limited
embedded Power MOSFET , so it is able to deliver
up to 3 A current to the load depending on the
application conditions.
The input voltage can range from 4.5 V to 28 V,
while the output voltage can be set starting from
0.6 V to VIN.
Requiring a minimum set of external components,
the device includes an internal 250 kHz switching
frequency oscillator that can be externally
adjusted up to 1 MHz.
The QFN and the HSOP packages with exposed
pad allow reducing the RthJA down to 60°C/W and
40°C/W respectively.
Figure 1. Application circuit
Contents L7981
2/42 DocID15182 Rev 5
Contents Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
5.3 Error amplifier and compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4 Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.5 Enable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.6 Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Application informations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.4.1 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.4.2 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1 Positive buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.2 Inverting buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
DocID15182 Rev 5 3/42
L7981 Contents Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Pin settings L7981
4/42 DocID15182 Rev 5
1 Pin settings
1.1 Pin connection
1.2 Pin description

Table 1. Pin description
DocID15182 Rev 5 5/42
L7981 Maximum ratings
2 Maximum ratings

3 Thermal data

Table 2. Absolute maximum ratings
Table 3. Thermal data Package mounted on demonstration board.

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