UM1556 Datasheet, PDF (45/87 Pages) STMicroelectronics – VIPower M0-5 and M0-5Enhanced

UM1556
Switching inductive loads
– Battery voltage:
V_BAT = 16 V
– HSD:
Clamping voltage:
VND5E160AJ
V_CLAMP = 46 V (typical for M0-5/M0-5E)
– Relay:
NVF4-4C-Z60a
Resistance:
R = 62 Ω@-40°C⁽¹⁾
Inductance (coil not powered): ^{L = 260 mH(2)}
– Load current (before turn-off
event):
I₀ = V_BAT/R = 258 mA
1. The relay datasheet usually specifies a coil resistance at 20 °C. For the worst case evaluation we should
consider the resistance at -40 °C which can be calculated as:
R_–40 = R₂₀ ⋅ (1 + 0.0039 ⋅ (– 40 – 20))
2. Not every relay datasheet specifies the coil inductance. In this case it can be determined by measurement.
The inductance value is different with armature seated (relay powered) than when unseated (relay not
powered). The inductance measurement should be done with relay powered (armature seated) because
this better represents the application conditions. The inductance of a typical 12 V automotive relay is in the
range of 200-800 mH.
Step 1) Demagnetization voltage calculation using Equation 11:
V_DEMAG = V_BAT – V_CLAMP = 16 – 46 = –30V
Step 2) Demagnetization time calculation using Equation 12:
T_DEMAG
=
R^-L--
⋅

 log

--^V----^D----^E--_V--^M--_D---^A-_E--^G--_M-----_A^+---_G--^I--⁰-----^â‹---^R--_{}
=
0_----._-62---2-6_---0_--
⋅
log


3_----0_-----+-----0_---3.--2_-0--5_---8_-----⋅_---6_---2_{--}
=
1.8ms
Step 3) Calculation of energy dissipated in HSD using Equation 14:
E_HSD = ^V-----^B----^A---^T-----+----_R--^V---₂--^D----^E---^M-----^A----^G---- ⋅ L ⋅
R ⋅ I₀– V_DEMAG
⋅
log



--^V----^D----^E--_V--^M--_D---^A-_E---^G-_M-----_A^+---_G--^I--⁰-----^â‹---^R-- _{}
=
=
1_----6_{-6----+2---2--}3_---0_{-- ⋅ 0.260 â‹}
62
⋅
0.258
–
30
⋅
log


3_----0_-----+-----0_---3.--2_-0--5_---8_-----⋅_---6_---2_{--}
= 9.9mJ
Step 4) HSD datasheet analysis:
The maximum demagnetization energy is specified by I/L diagram in the datasheet. This
diagram shows the maximum turn-off current versus inductance for R_L = 0 Ω and
V_BAT = 13.5 V (see Figure 39). These conditions are different from conditions considered in
our example (R_L = 62 Ω, V_BAT = 16 V) and inductance 260 mH is not covered by the
diagram.
Doc ID 023520 Rev 2
45/87