L9918 datasheet(16/109 Pages) STMICROELECTRONICS

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Figure 6. Dependency between B+ and EXC duty cycle in case of P_ANT regulation and I_ANT variation

Set point

Set point – P_ANT

100%

50%

EXC DC

B+

I_ANT variation

Alternator

output voltage

Set point

Set point – 100mV

Set point – 200mV

Set point – P_ANT

Set point –

100%

P_ANT

P_ANT regulation

I_ANT = 0 mV

I_ANT = -100

I_ANT

= -200

I_ANT

= OFF

2.2.3

Thermal compensation

Thermal compensation function is a protection function whose aim is to reduce current flowing out from EXC pin

when a too high junction temperature is sensed.

This function operates as reported in Figure 6. Adopted set point is gradually reduced in case measured Tj is

greater than thermal compensation threshold THT.

THT threshold can be programmed by HT_KN NVM bits. In some LIN configuration an offset can be added to

HT_KN (Section A.7 Voltage limitation for high temperatures), so that THT = HT_KN + LIN offset. Maximum

value of the adopted THT value is furthermore clamped to HT_KN_MAX. This means that the operative THT value

is chosen as the minimum between HT_KN_MAX and HT_KN + LIN offset.

Once thermal compensation function is active, maximum set point is reduced accordingly to SHT slope [mV/C]

which can be set by NVM register HTK_SLOPE. As Tj increase, the maximum adopted set point decreases.

Thermal compensation dynamic behaviour is influenced by NVM bits G_HT, by which is possible to select the

desired set point variation time gradient.

A further option related to thermal compensation is selectable by NVM bit HTKMAX_EN. This bit enables a

temperature threshold THTmax over which adopted setpoint is forced to 10.6 V. THTmax value is fixed to 176 °C.

In case the NVM bit ANZ_HT_EN = 0x1, F_T LIN flag is set to "1" as soon as the set point currently adopted is

modified by thermal compensation.

Figure 7. Thermal compensation

VBSPLINRG = 16V

VBSPLINRG = 10.6V

Adopted Set point

(VBSPLINRR/ VBSPDEF)

THT

SHT

TjHT THTmax

Tshd

L9918

B+ characteristics

DS13000 - Rev 2

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