L99DZ80EP datasheet(34/68 Pages) STMICROELECTRONICS

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L99DZ80EP

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DocID18260 Rev 6

3.8

Inductive loads

Each half bridge is built by internally connected high- and low-side power DMOS transistors.

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

the outputs OUT1 to OUT6 without external freewheeling diodes. The high-side drivers

OUT7 to OUT11 are intended to drive resistive loads. Therefore only a limited energy

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

inductive loads (L > 100 µH) an external freewheeling diode connected between GND and

the corresponding output is required. The low side driver at ECV does not have a freewheel

diode built into the device.

3.9

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 tFOL 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. 3 ms) can be used to test the open load status without

changing the mechanical/electrical state of the loads.

3.10

Overcurrent detection

In case of an overcurrent condition, a flag is set in the status register. If the overcurrent

signal is valid for at least TFOC, the overcurrent flag is set and the corresponding driver is

switched off to reduce the power dissipation and to protect the integrated circuit. If the

overcurrent recovery bit of the output is cleared, the microcontroller has to clear the status

bits to reactivate the corresponding driver.

3.11

Current monitor

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

three fixed ratios of the instantaneous current of the selected high-side driver. Outputs with

a resistance of 500 m

and higher have a ratio of 1/2000, except for OUT8, which has a

ratio of 1/6500, and those with a lower resistance one of 1/10000. The signal at output CM is

blanked after switching on the driver until correct settlement of the circuitry. The bits

CM_SEL<3:0> define which of the outputs are multiplexed to the current monitor output CM.

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, it can be used to

detect the motor state (starting, free running, stalled). Moreover, it is possible to control the

power of the defroster more precisely by measuring the load current. The current monitor

output is enabled after the current-monitor blanking time, when the selected output is

switched on. If this output is off, the current monitor output is in high-impedance mode.

3.12

PWM mode of the power outputs

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

interface. If the PWM enable bit is set, the output is controlled by the logically AND-

combination of an internally generated PWM signal and the output control bit of the

corresponding driver. The PWM-Frequency of all outputs can be programmed to either

122 Hz of 244 Hz typically. The on-duty-cycle is set by the four 7-bit registers, which control

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