Other L9733 features

L9733

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DocID11319 Rev 12

6

Other L9733 features

6.1

Charge pump usage

In order to provide low Rdson values when connected in a high-side configuration, a charge

pump to drive the internal gate voltage(s) above Vbat is implemented. The charge pump

used on the L9733 doesn't need external capacitor. The L9733 uses a common charge

pump and oscillator for all the 8 configurable output channels. The charge pump uses the

Vbat supply connected directly to the Vb pin. The normal range of the Vbat voltage is 10 to

18V18V. However, the L9733 is functional with Vbat voltages as low as 4.5 V DC with

eventually a degradation of Rdson.

The frequency range of this charge pump is from 3.6 to 7.6 MHz. The frequency is above

1.8 MHz in order to be above the AM radio band and below 8.0 MHz so that harmonics do

not get within the FM radio band.

6.2

Waveshaping

Both the turn on and the turn off slew rates on all outputs (OUT1-8) are limited to between

10 μs and 100 μs for both rise and fall times (10 to 90 %, and vice versa), to reduce

conducted EMC energy in the vehicle's wiring harness. The characteristics of the turn-on

and turn-off voltage is linear, with no discontinuities, during the output driver state transition.

6.3

POR register initialization

When the L9733 wakes up, the Vdd supply to the L9733 is allowed from 0 to 5 VDC in 0.3 to

3ms. The L9733 has a POR circuit, which monitors the Vdd voltage. When the Vdd voltage

reaches an internal threshold, and remains above this trip level for at least 5 to 20 μs, the

Command and Fault registers are "cleared". Before Vdd reaches this trip level, none of the

eight outputs are allowed to momentarily glitch on.

6.4

Thermal shutdown

Each of the eight outputs has independent thermal protection circuitry that disables each

output driver once the local N-Channel MOSFET's device temperature reaches between

+151 and +200 °C. A filter is present to validate the thermal fault (5 μs to 20 μs). There is a

5 to 15 °C hysteresis between the enable and disable temperature levels. The faulted

channel will periodically turn off and on until the fault condition is cleared, the ambient

temperature is decreased sufficiently or the output is commanded off. If a thermal shutdown,

of one or more output drivers, is active during the falling edge of the chip select (CS) signal

all the bits of the Fault Register are "set" to "1" (thermal shutdown is not latched and could

be read only in the moment it is present). The thermal fault is cleared on the rising edge of

Chip Select if a valid DI byte is received.

Note:

Due to the design of the L9733 each output's thermal limit "may not" be truly independent to

the extent that if one output is shorted, it may impact the operation of other outputs (due to

lateral heating in the die).