L9524C datasheet(18/27 Pages) STMICROELECTRONICS

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Functional description

L9524C

18/27

In relay mode (modes 1 and 2) the positive sense input pins are short-circuited since the

relay is the only switch. In transistor mode (modes 3 to 6) glow plug 5 is switched with

transistor 2 and glow plug 6 with transistor 4. Therefore only 4 positive sense input pins are

necessary.

If the voltage drop across the sense resistor is less than

ΔV

OL for at least tOL fil an open-load

failure is detected as long as VVS > VVS ol. If it is greater than ΔVOC (see below for definition)

for at least tOC fil an overcurrent failure is detected and the corresponding switch is switched

off and remains switched off until power-down. The threshold for overcurrent failures

ΔV

can be varied by the voltage applied to the OCT pin (see section “Overcurrent threshold

variation”).

In modes 1 to 4 the overcurrent threshold is constant with respect to the temperature

(TCOC = 0). But in modes 5 and 6 the overcurrent threshold increases linearly with the

temperature

ϑ to compensate the first-order temperature coefficient of the R

DS(on) of the

external power MOSFET’s which are used as sense resistors in these modes:

Equation 1

ΔV

OC = ΔVOC 0 (1 + TCOC (ϑ + 40°C)).

4.6

Switch monitoring

The L9524C monitors the voltages across the glow plugs (using the negative sense input

pins SN1, SN2, SN3, and SN4) to detect if the corresponding switches work properly or not.

A switch is detected as defect if it is switched on but the voltage across the corresponding

glow plug(s) is less than VSD for at least tSD fil or if it is switched off but the voltage across

the glow plug(s) is greater than VSD for at least tSD fil.

4.7

Thermal shutdown

If the junction temperature becomes greater than TJSD all glow plugs are switched off. They

are switched on again if the junction temperature falls below TJSD.

4.8

Gate drivers

The L9524C contains four gate drivers (Gx pins) for external n-channel power MOSFET’s in

high-side configuration. Each gate driver provides a slope control by charging and

discharging the gates of the external power MOSFET’s with constant currents (IG on or IG

off). To adjust the slopes these currents can be varied using the CUR pin (see section “Gate

charge/discharge current variation”). The charging current source is supplied by an external

capacitor connected to the charge pump output (CP) pin. The gate-to-source voltages are

limited internally and without supply voltage (VVS) the gates and the sources of the external

power MOSFET’s are short-circuited.

During free-wheeling of inductive loads the gates of the external power MOSFET’s are

clamped to VG cl. As a result, the power MOSFET’s become conducting and the energy in

the inductive loads is recirculated through the power MOSFET’s.

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