AN937 Datasheet, PDF (17/29 Pages) STMicroelectronics – The L4971 is a 1.5 A monolithic dc-dc converter

AN937
3
Typical application
Typical application
Figure 22 shows the typical application circuit, where the input supply voltage, Vcc, can
range from 8 to 55 V operating, and the output voltage adjustable from 3.3 V to 40 V.
The selected components, and in particular input and output capacitors, are able to sustain
the device voltage ratings, and the corresponding RMS currents.
3.1
Electrical specification
● Input voltage range: 8 V - 55 V
● Output voltage: 5.1 V ±3% (Line, load and thermal)
● Output ripple: 51 mV
● Output current range: 1 mA - 1.5 A
● Max output ripple current: 30% Iomax
● Max output current: 1.5 A
● Switching frequency: 200 kHz
Figure 21. Application circuit
VIN
C1
180u 63v
INH
C2
220n
63V
R1
L4971 DIP 8 U1
12k
3 _OSC
2 _SS/INH
C7 100n 100V
OUT ⁴
VFB ⁸
L1
120uH (CC MSS1260-124KLD)
C9
4.7n
R5
C3
C6
R4
2.2n
220n
15k
C8
C5
82p
C4
GND
22n
VOUT
R2
2.7k
R3
4.99k
C10
150uF
C11
100n
GND
3.2
Input capacitor
The input capacitor has to be able to support the max input operating voltage of the device
and the max rms input current. The input current is squared and the quality of these
capacitors has to be very high to minimize its power dissipation generated by the internal
ESR, improving the system reliability. Moreover, input capacitors are also affecting the
system efficiency.
The max Irms current flowing through the input capacitors is:
Doc ID 5655 Rev 15
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