AN2791

Root Part Number 1 overview

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Root Part Number 1 overview

The Root Part Number 1 (see Figure 1) is designed to drive inductive loads (e.g. relays,

electromagnetic valves, etc.) in low side configuration. Integrated active Zener-clamp, for

channels 1 and 2, or free wheeling diodes, for channels 3 and 4, allow the recirculation of

the current of the inductive loads during the off-state of the DMOS.

All four channels are monitored with a status output. All wiring to the loads and supply pins

of the device are controlled.

The device is self-protected against short circuit at the outputs and over-temperature.

Channels 3 and 4 work as current regulator.

A PWM signal, with a 2 kHz frequency, on the input defines the target for the output current,

in particular, there is a linear relationship between the duty-cycle of the PWM input signal

and the target value of the current (see Figure 2).

The current is measured during recirculation phase of the load, that is, during the off-state of

the DMOS. A sensing resistor, integrated in the IC and placed on the drain of the DMOS and

of the free-wheeling diode, is devoted to measure the current.

The benefit of the current regulation is an optimization of the PWM duty-cycle strategy

against changes in the load conditions (e.g. temperature gradient and as a consequence

coil resistor increases). Moreover, a test mode compares the differences between the two

regulators. This "drift" test compares the output PWM of the regulators. Using this feature a

drift of the load during lifetime can be detected.

Figure 1.

Root Part Number 1 application diagram

LOGIC

Overload

Open Load

GND-det.

Overtemperature

Channel 1

Overtemperature

Channel 4

LOGIC

&

DA

Overload

Open Load

GND-det.

IPD

IPD

LOGIC

Overload

Open Load

GND-det.

Overtemperature

Channel 2

Overtemperature

Channel 3

LOGIC

&

DA

Overload

Open Load

GND-det.

IPD

IPD

drift-det.

VS

VCC

VDD

Q1

Free wheeling valve

Free wheeling valve

Regulated valve

Regulated valve

D4

Q4

Q2

D3

Q3

GND

TEST

ST3

IN3

ST2

IN2

ST4

IN4

ST1

IN1

CLK

EN

Internal Supply

Microcontroller

5 V logic supply

Vbatt