ST EVAL5981 User Manual

1 A step-down switching regulator demonstration board
Features
1 A DC output current
2.9 V to 18 V input voltage
Output voltage adjustable from 0.6 V to 16 V
up to 1 MHz
Internal soft-start and inhibit
Low dropout operation: 100 % duty cycle
Zero-load current operation
Over-current and thermal protection
VFQFPN8 3 mm x 3 mm package
EVAL5981
based on the L5981
Data Brief
EVAL5981
Description
The EVAL5981 demonstration board provides the design engineer with a fully functional step-down switching regulator with an output current of up to 1 A. The L5981 integrates STMicroelectronics step-down switching regulator, together with all the external components required for a typical application.
The rated voltage of the input capacitor and the Schottky diode rectifier repetitive peak reverse voltage are both 25 V, making the board capable of covering the entire 2.9 V - 18 V input voltage range of the L5981 device.
The board features an external resistor divider (R1 and R2) designed for an output voltage of 3.3 V.
The output voltage can be set to a level from 0.6 V up to the rated voltage of the output capacitor (16 V).
The compensation network on the demonstration board allows the use of MLCC as output filter to keep the loop stable. The inductor saturation current and forward current of the Schottky diode are within the current limit values.
The switching frequency on the demonstration board is set to 500 kHz by means of the R5 resistor connected to pin Fsw.
March 2009 Rev 1 1/6
For further information contact your local STMicroelectronics sales office.
www.st.com
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EVAL5981 EVAL5981 application circuit and component list

1 EVAL5981 application circuit and component list

Figure 1. Application circuit

L1 15uH
VCC
VCC
VCC
VIN=3.3V to 18V
VIN=3.3V to 18V
VIN=3.3V to 18V
VIN=3.3V to 18V
C1
C1
C1
C1
10uF
10uF
10uF
10uF
C6
C6
C6
C6
68nF
68nF
68nF
68nF
VCC
INH
INH
INH
INH
GND
GND
GND
GND
R5 100K
R5 100K

Table 1. Component list

OUT
OUT
OUT
OUT
1
1
1
1
1
1
1
4
4
4
4
1
2
2
2
2
5
5
5
5
R4 3.9K
R4 3.9K
C5 150pF
C5 150pF
SYNCH
SYNCH
SYNCH
SYNCH
FB
FB
FB
FB
C4 10nF
C4 10nF
C4 10nF
C4 10nF
8
8
8
8
3
3
3
3
L5985
L5981
L5985
FSW
FSW
FSW
FSW
6
6
6
6
L5981
COMP
COMP
COMP
COMP
COMP
COMP
COMP
COMP
7
7
7
7
L1 15uH
D1
D1
D1
D1
STPS2L25U
STPS2L25U
STPS2L25U
STPS2L25U
R1 4.99K
R1 4.99K
R1 4.99K
R1 4.99K
R2 1.1K
R2 1.1K
R2 1.1K
R2 1.1K
Vout=3.3V
Vout=3.3V
Vout=3.3V
Vout=3.3V
C2
C2
C2
C2
22uF
22uF
22uF
22uF
C3 3.3nFR3 180
C3 3.3nFR3 180
Reference Part number Description Manufacturer
C1 GRM31CR61E106KA12 10 μF, 25 V MURATA
C2 GRM32ER61E226KE15 22 μF, 25 V MURATA
C3 3.3 nF, 50 V
C4 10 nF, 50 V
C5 150 pF, 50 V
C6 68 nF, 25 V
R1 4.99 kΩ, 1 %, 0.1 W 0603
R2 1.1 kΩ, 1 %, 0.1 W 0603
R3 180 Ω, 1 %, 0.1 W 0603
R4 3.9 kΩ, 1 %, 0.1 W 0603
R5 100 kΩ, 1 %, 0.1 W 0603
D1 STPS2L25V 2 A, 25 V STMicroelectronics
L1 7447779115 15 μH, 20 %, 2.2 A Wurth elektronik
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EVAL5981 PCB layout

2 PCB layout

Figure 2. PCB layout (component side)

Figure 3. PCB layout (bottom side)

Figure 4. PCB layout (front side)

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EVAL5981 Package mechanical data

3 Package mechanical data

In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK specifications, grade definitions and product status are available at: www.st.com. ECOPACK
®
packages, depending on their level of environmental compliance. ECOPACK®
®
is an ST trademark.
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EVAL5981 Revision history

4 Revision history

Table 2. Document revision history

Date Revision Changes
02-Mar-2009 1 Initial release
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EVAL5981
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