L9954 Datasheet L9954XP, L9954XPTR, L9954 | P19-P21

L9954 / L9954XP Application information

Doc ID 14279 Rev 4 19/37

3 Application information

3.1 Dual power supply: V

and V

The power supply voltage V

supplies the half bridges and the highside drivers. An internal

charge-pump is used to drive the highside switches. The logic supply voltage V

(stabilized 5 V) is used for the logic part and the SPI of the device.

Due to the independent logic supply voltage the control and status information will not be

lost, if there are temporary spikes or glitches on the power supply voltage. In case of power-

on (V

increases from undervoltage to V

POR OFF

= 4.2 V) the circuit is initialized by an

internally generated power-on-reset (POR). If the voltage V

decreases under the

minimum threshold (V

POR ON

= 3.4 V), the outputs are switched to tristate (high impedance)

and the status registers are cleared.

3.2 Standby mode

The standby mode of the L9954 is activated by clearing the bit 23 of the Input Data Register

0. All latched data will be cleared and the inputs and outputs are switched to high

impedance. In the standby mode the current at V

) is less than 6 µA (50µA) for

CSN = high (DO in tristate). By switching the V

voltage a very low quiescent current can

be achieved. If bit 23 is set, the device will be switched to active mode.

3.3 Inductive loads

Each half bridge is built by an internally connected highside and a lowside power DMOS

transistor. Due to the built-in reverse diodes of the output transistors, inductive loads can be

driven at the outputs OUT1 to OUT3 without external free-wheeling diodes. The highside

drivers OUT4 to OUT6 are intended to drive resistive loads. Hence only a limited energy

(E<1mJ) can be dissipated by the internal ESD-diodes in freewheeling condition. For

inductive loads (L>100μH) an external free-wheeling diode connected to GND and the

corresponding output is needed.

3.4 Diagnostic functions

All diagnostic functions (over/open load, power supply over-/undervoltage, temperature

warning and thermal shutdown) are internally filtered and the condition has to be valid for at

least 32 µs (open load: 1ms, respectively) before the corresponding status bit in the status

registers will be set. The filters are used to improve the noise immunity of the device. Open

load and temperature warning function are intended for information purpose and will not

change the state of the output drivers. On contrary, the overload condition will disable the

corresponding driver (over-current) and overtemperature will switch off all drivers (thermal

shutdown). Without setting the over-current recovery bits in the Input Data register, the

microcontroller has to clear the over-current status bits to reactivate the corresponding

drivers.

Application information L9954 / L9954XP

20/37 Doc ID 14279 Rev 4

3.5 Overvoltage and undervoltage detection

If the power supply voltage V

rises above the overvoltage threshold V

SOV OFF

(typical 21

V), the outputs OUT1 to OUT6 are switched to high impedance state to protect the load.

When the voltage V

drops below the undervoltage threshold V

SUV OFF

(UV-switch-OFF

voltage), the output stages are switched to the high impedance to avoid the operation of the

power devices without sufficient gate driving voltage (increased power dissipation). If the

supply voltage V

recovers (register 0: bit 20=0) to normal operating voltage the outputs

stages return to the programmed state after at least 32 µs.

If the undervoltage/overvoltage recovery disable bit is set, the automatic turn-on of the

drivers is deactivated. The microcontroller needs to clear the status bits to reactivate the

drivers. It is strongly recommended to set bit 20 to avoid a possible high current oscillation in

case of a shorted output to GND and low battery voltage.

3.6 Charge pump

The charge pump runs under all conditions in normal mode. In standby the charge pump is

out of action.

3.7 Temperature warning and thermal shutdown

If junction temperature rises above T

j TW

a temperature warning flag is set after at least 32

µs and is detectable via the SPI. If junction temperature increases above the second

threshold T

j SD

, the thermal shutdown bit will be set and power DMOS transistors of all

output stages are switched off to protect the device after at least 32 µs. Temperature

warning flag and thermal shutdown bit are latched and must be cleared by the

microcontroller. The related bit is only cleared if the temperature decreases below the

trigger temperature. If the thermal shutdown bit has been cleared the output stages are

reactivated.

3.8 Open-load detection

The open load detection monitors the load current in each activated output stage. If the load

current is below the open load detection threshold for at least 1 ms (t

dOL

) the corresponding

open load bit is set in the status register. Due to mechanical/electrical inertia of typical loads

a short activation of the outputs (e.g. 3ms) can be used to test the open load status without

changing the mechanical/electrical state of the loads.

3.9 Over load detection

In case of an over-current condition a flag is set in the status register in the same way as

open load detection. If the over-current signal is valid for at least t

ISC

= 32 µs, the over-

current flag is set and the corresponding driver is switched off to reduce the power

dissipation and to protect the integrated circuit. If the over-current recovery bit of the output

is zero the microcontroller has to clear the status bits to reactivate the corresponding driver.

L9954 / L9954XP Application information

Doc ID 14279 Rev 4 21/37

3.10 Current monitor

The current monitor output sources a current image at the current monitor output which has

a fixed ratio (1/10000) of the instantaneous current of the selected highside driver. Signal at

output CM is blanked after switching on of driver until correct settlement of circuitry (at least

for 32 µs).

The bits 18 and 19 of the Input Data Register 0 control which of the outputs OUT1, OUT4,

OUT5 and OUT6 will be multiplexed to the current monitor output. The current monitor

output allows a more precise analysis of the actual state of the load rather than the detection

of an open- or overload condition. For example this can be used to detect the motor state

(starting, free-running, stalled). Moreover, it is possible to regulate the power of the defroster

more precise by measuring the load current. The current monitor output is bidirectional (c.f.

PWM inputs).

3.11 PWM inputs

Each driver has a corresponding PWM enable bit which can be programmed by the SPI

interface. If the PWM enable bit in Input Data Register 1 is set , the output is controlled by

the logically AND-combination of the PWM signal and the output control bit in Input Data

output OUT5 is controlled by the bidirectional input CM/PMW2. For example, the two PWM

inputs can be used to dim two lamps independently by external PWM signals.

3.12 Cross-current protection

The three half-bridges of the device are cross-current protected by an internal delay time. If

one driver (LS or HS) is turned-off the activation of the other driver of the same half bridge

will be automatically delayed by the cross-current protection time. After the cross-current

protection time is expired the slew-rate limited switch-off phase of the driver will be changed

to a fast turn-off phase and the opposite driver is turned-on with slew-rate limitation. Due to

this behavior it is always guaranteed that the previously activated driver is totally turned-off

before the opposite driver will start to conduct.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P33 P34-P36 P37-P37

L9954

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IC DVR DOOR ACTUATOR POWERSO-36

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