L9848

Functional description

19/27

3.10

Thermal shutdown

Each of the 8 outputs have independent thermal protection circuitry that disables each

output driver once the local n-channel MOSFET device temperature reaches the

overtemperature shutdown limit. Due to the hysteresis of 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.

Once any individual channel goes into thermal shutdown, a logic "1" is latched into the Fault

Register if it meets the thermal fault filter (Note: does NOT go through the open/short fault

filter).

Note:

Due to the design of the L9848 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). The user may be required to monitor the fault bits periodically. If a

fault bit is "Set" for the last enabled output, and subsequently, fault bits for other enabled

outputs start to be "Set", the user will send two SPI write cycles within 100ms of each other.

The first SPI write cycle will "Clear" the fault latches. If multiple faults are indicated after the

second SPI write cycle, these faults are most likely thermal faults. The user will then disable

this output that was most recently enabled. The fault register should be subsequently

interrogated to verify proper operations of the other enabled output channels.

3.11

Charge pump usage

The L9848 uses a separate charge pump and oscillator for each of the 6 configurable output

channels to provide low RDSON values when connected in a high side configuration These

oscillators are operating in a non-synchronous mode of operation. The frequency range of

these charge pumps is designed to be above the AM radio band and below 8.0 MHz so that

harmonics do not get within the FM radio band.

3.12

Waveshaping

Both the turn on and the turn off slew rates on all outputs (OUTPUT1-8) are limited to

reduce conducted EMC energy in the vehicle's wiring harness.

The characteristic of the turn-on and turn-off voltage is linear, with no discontinuities, during

the output driver state transition.

3.13

POR register initialization

L9848 wakes up if the VDD supply increases from 0 to 5VDC in 0.3ms to 3ms.

The L9848 has a POR circuit, which monitors the VDD voltage. When the VDD voltage

reaches roughly 4.1VDC, and remains above this trip level for minimum 20µs, the Command

and Fault Registers are "cleared". Before VDD reaches this trip level, all eight outputs are

guaranteed in OFF-state.

After a valid POR has occurred and the VDD voltage falls below the valid high level for a

required amount of time, the L9848 is powered down in a fully controlled manner. No

outputs will glitch "ON" and no erroneous fault data is allowed on the DO output.