Data Brief
For further information contact your local STMicroelectronics sales office.
March 2009 Rev 1 1/6
6
Features
■1 A DC output current
■2.9 V to 18 V input voltage
■Output voltage adjustable from 0.6 V to 16 V
■250 kHz switching frequency, programmable
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
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.
EVAL5981
EVAL5981
1 A step-down switching regulator demonstration board
based on the L5981
www.st.com
EVAL5981 EVAL5981 application circuit and component list
2/6
1 EVAL5981 application circuit and component list
Figure 1. Application circuit
Table 1. Component list
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
OUT
FB
SYNCH
INH
GND
COMP
VCC
L5985
C1
10uF C4 10nF
R1 4.99K
R2 1.1K
D1
STPS2L25U
L1 15uH
C3 3.3nFR3 180
C5 150pF
R4 3.9K
FSW
8
3
7
64
5
2
1
C2
22uF
C6
68nF
COMP
1
Vout=3.3V
VIN=3.3V to 18V
R5 100K
OUT
FB
SYNCH
INH
GND
COMP
VCC
L5981
C1
10uF C4 10nF
R1 4.99K
R2 1.1K
D1
STPS2L25U
FSW
8
3
7
64
5
2
1
C2
22uF
C6
68nF
COMP
1
Vout=3.3V
VIN=3.3V to 18V
OUT
FB
SYNCH
INH
GND
COMP
VCC
L5985
C1
10uF C4 10nF
R1 4.99K
R2 1.1K
D1
STPS2L25U
L1 15uH
C3 3.3nFR3 180
C5 150pF
R4 3.9K
FSW
8
3
7
64
5
2
1
C2
22uF
C6
68nF
COMP
1
Vout=3.3V
VIN=3.3V to 18V
R5 100K
OUT
FB
SYNCH
INH
GND
COMP
VCC
L5981
C1
10uF C4 10nF
R1 4.99K
R2 1.1K
D1
STPS2L25U
FSW
8
3
7
64
5
2
1
C2
22uF
C6
68nF
COMP
1
Vout=3.3V
VIN=3.3V to 18V
EVAL5981 PCB layout
3/6
2 PCB layout
Figure 2. PCB layout (component side)
Figure 3. PCB layout (bottom side)
Figure 4. PCB layout (front side)
EVAL5981 Package mechanical data
4/6
3 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK® is an ST trademark.
EVAL5981 Revision history
5/6
4 Revision history
Table 2. Document revision history
Date Revision Changes
02-Mar-2009 1 Initial release
EVAL5981
6/6
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