AN557 datasheet(33/52 Pages) STMICROELECTRONICS

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AN557 APPLICATION NOTE

Figure 42. Test and Evaluation Board Circuit

TYPICAL PERFORMANCES (using evaluation board) :

n = 83% (Vi = 35V ; Vo = VREF ; Io = 7A ; fSW = 200KHz); Vo RIPPLE = 30mV (at 7A) with output filter ca-

pacitor ESR

≤ 60mΩ; Line regulation = 5mV (Vi = 15 to 50V); Load regulation = 15mV (Io = 2 to 7A); For

component values, refer to test circuit part list.

PARTS LIST

* 2 capacitors in parallel to increase input RMS current capability

** 3 capacitors in parallel to reduce total output ESR

Table A

Table B - SUGGESTED BOOTSTRAP CAPACITORS

R1 = 30K

Ω

R11 = 10

Ω

R2 = 10K

Ω

* C1, C2 = 3300

µF 63VL EYF (ROE)

R3 = 15K

Ω

C3, C4, C5, C6 = 2.2

µF

R4 = 16K

Ω

C7 = 390pF Film

R5 = 22

Ω 0,5W

C8 = 22nF MKT 1817 (ERO)

R6 = 4K7

C9 = 2.2nF KP1830

R7 = 10

Ω

C10 = 220nF MKT

R8 = see tab. A

C11 = 2.2nF MP1830

R9 = OPTION

**C12, C13, C14 = 220

µF 40VL EKR

R10 = 4K7

C15 = 1

µF Film

D1 = MBR 1560CT (or 16A/60V or equivalent)

L1 = 40

µH

core 58071 MAGNETICS 27 TURNS Ø 1,3mm (AWG 16) COGEMA 949178

R10

12V

4.7K

Ω

6.2K

Ω

15V

4.7K

Ω

9.1K

Ω

18V

4.7K

Ω

12K

Ω

24V

4.7K

Ω

18K

Ω

Operating Frequency

Bootstrap Cap.c10

f = 20KHz

≥680nF

f = 50KHz

≥470nF

f = 100KHz

≥330nF

f = 200KHz

≥220nF

f = 500KHz

≥100nF

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