UM1693 datasheet(90/196 Pages) STMICROELECTRONICS

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Load compatibility

UM1693

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Measurement example – switching losses versus L (VND7040AJ-E)

In order to get a better idea about the switching losses dependency on the value of the

inductance, a comparative measurement with different load inductances was performed on

VND7040AJ-E. The summary of this measurement is shown in the tables below. The

Table 21 describes the steady state operation (single turn-on / off event), with or without an

external freewheeling diode. For each load inductance, there is a measurement of switching

losses and switching times (time between 10-90 % of nominal VOUT considered). All

switching losses are compared versus the resistive load. In the last column there is a

calculation of demagnetization time (considering VDEMAG = -28 V).

VBAT = 16 V Single turn-on (ILOAD = 0), single turn-off (ILOAD = nominal = 1.2 A)

The Table 22 describes the PWM operation with high duty cycle (shortest possible PWM off-

time adjusted to have complete turn-off / on phase). The measurement was done with

external freewheeling only (Schottky diode). In the last column there is a calculation of

demagnetization time (considering VDEMAG = -0.6 V).

VBAT = 16 V PWM 94 % at 500 Hz (120 µs off-time) → shortest possible for complete turn-

off/on phase

Table 21. VND7040AJ-E measurement of switching losses versus L in steady state

Load

WON

WOFF

(with external

freewheeling)

tON [µs]

tOFF

[µs]

TDEMAG

(calculated)

L [µH]

R [

Ω][µJ]

Ratio vs

res. load

[µJ]

Ratio vs

res. load

[µJ]

Ratio vs

res. load

10-90%

of VOUT

90-10%

of VOUT

(at -28 V)

[µs]

1.5

13.5

139

1.00 x

157

1.00 x

157

1.00 x

0.0

13.5

130

0.94 x

173

1.10 x

173

1.10 x

0.5

13.5

116

0.83 x

204

1.30 x

204

1.30 x

1.9

300

13.5

0.50 x

382

2.43 x

321

2.04 x

9.5

1 000

13.5

0.39 x

785

5.00 x

438

2.79 x

3 500

13.5

0.37 x

2 370

15.1 x

492

3.13 x

111

5 400

13.5

0.36 x

3 470

22.1 x

487

3.10 x

171

20 000

13.5

0.08 x

13 630

86.82 x

533

3.39 x

633

Table 22. VND7040AJ-E measurement of switching losses versus L in PWM mode (with external

freewheeling)

Load

WON

(with external

freewheeling)

WOFF

(with external

freewheeling)

tON [µs]

tOFF [µs]

TDEMAG

(calculated)

L [µH]

R [

Ω][µJ]

Ratio vs

res. load

[µJ]

Ratio vs

res. load

(10-90% of

VOUT)

(90-10% of

VOUT)

(at -0.6V) [µs]

1.5

13.5

139

1.00

157

1.00

0.0

13.5

130

0.94

173

1.10

13.5

118

0.85

205

1.31

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