UM1556 datasheet(41/87 Pages) STMICROELECTRONICS

41 / 87 page

UM1556

Switching inductive loads

Doc ID 023520 Rev 2

41/87

direction. This voltage (so called demagnetization voltage) is limited to the value given by

the clamping voltage of the HSD and the battery voltage:

Equation 11

The load current decays exponentially (linearly if R

→0) and reaches zero when all energy

stored in the inductor is dissipated in the HSD and the load resistance.

Since the HSD output clamp is related to the VBAT pin, the energy absorbed by the HSD

increases with increasing battery voltage (the battery is in series with the high side switch

and load so the energy contribution of the battery increases with the battery voltage).

4.2.1

Calculation of energy dissipated in the HSD

The energy dissipated in the High Side Driver is given by the integral of the actual power on

the MOSFET through the demagnetization time:

To integrate the above formula we need to know the current response iOUT(t) and the

demagnetization time TDEMAG. The IOUT(t) can be obtained from the well known formula,

R/L circuit current response using the initial current I0 and the final current VDEMAG/R

considering iOUT >= 0 condition (see Figure 37):

(0 < t < TDEMAG→ iOUT ≥ 0)

Inserting i(t) = 0 we can calculate the demagnetization time:

Equation 12

Equation 13

DEMAG

BAT

CLAM P=

–

13V - 46V typ.

HSD

CLAMP

DEMAG



OU T(t)dt

⋅

OUT(t)

DEMAG

---------------------------





–

---------

–







⋅







–

DEMAG

----

DEMAG

0 R

⋅

DEMAG

-----------------------------------------------







log

⋅

DEMAG

→

lim

DEMAG

------------------------

⋅

UM1556 Datasheet(PDF) 41 Page - STMicroelectronics

UM1556 Datasheet(HTML) 41 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Datasheet Download

Link URL