L9918 datasheet(7/109 Pages) STMICROELECTRONICS

7 / 109 page

1.4.6

Voltage divider & ΣΔ modulator for overvoltage/undervoltage

The stage has a resistive divider connected to battery (different and independent of the previous stage) and

provides the correct signal voltage range to the internal data converter. The stage feeds into the digital block a

bit-stream converted in a digital code with a proper low pass filter. The code is managed in the digital block to

implement the overvoltage and under-voltage detections.

1.4.7

Thermal sensor

Thermal sensor provides to the digital block the device temperature. The block embeds a thermal sensor and a

sigma-delta converter whose bit-stream is converted in a digital code.

1.4.8

Oscillator

The block provides the clock reference for the digital function and the Charge Pump block. The frequency value is

16MHz ± 5%.

1.4.9

Excitation driver

The block embeds a power N-channel MOS inserted between B+ and EXC pins and a circuitry that is able to

drive it. A freewheeling circuit is inserted between EXC and GND pins, located across the excitation coil for

energy recirculation purpose. The protection against short circuit on EXC pin is also implemented. If a short circuit

is detected the excitation current is turned off and the subsequent turn-on attempt is retried at every excitation

period.

A current measurement block provides the excitation current value flowing in the high-side power MOS. In order

to reach the requested accuracy, a dedicated thermal sensor is located close to the current measurement block.

Power MOS temperature is used to calibrate the current measure.

1.4.10

Safety switch OFF

Safety Switch OFF is a separate block featured for safety reason. It must switch the field driver power MOS gate

off when a battery overvoltage condition is detected.

1.4.11

Charge pump

Charge pump is mandatory to supply correctly the excitation power MOS gate.

1.4.12

Non volatile memory (NVM)

The NVM allows to set all configurable device parameters. Please refer to default mode parameter table (see

Section A.1 ).

1.4.13

Digital block

All device functions are managed by the digital block. The state diagram is shown in the next chapter.

1.5

State diagram

The following figure describes L9918 state machine.

L9918

State diagram

DS13000 - Rev 2

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