Functional description

L5953

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Functional description

2.1

REG1 stand-by regulator

The stand-by regulator (

Figure 7.) output voltage can be 5V or 3.3V. It is externally

selectable by means of the ADJ pin:

- leaving the ADJ pin open, the output voltage is 5V;

- connecting the ADJ pin to the Vstby pin the output voltage becomes 3.3V.

This regulator is supplied by STCAP pin and provide the reset information.

It has a current protection which limits the maximum allowable output current.

2.2

Reset

The RES pin (

Figure 8.) is an open collector that is activated (that is forced to zero) when

the stand-by regulator is not in regulation (including thermal shutdown and faults). The

indication that REG1 is in regulation is delayed by a time set up by the external capacitor CT.

When the RES is switched on, HSD1, HSD2, REG2, PWM are turned off and until the RES

is forced to zero only the REG1 and low Voltage Warnings are active.

2.3

Low voltage warning

This circuit is able to sense two different voltages through external resistors to increase the

overall flexibility. (

Figure 9.)

If S1 pin voltage is higher than Vst, the output of mos M1 is off: W1 is floating and can be

pulled up by an external resistor. If S1 pin voltage goes down and becomes lower than Vst,

the mos M1 is turned on and forces W1 to zero. The same thing happens for S2 - W2.

The outputs W1 and W2 can be connected together to get a single output.

2.4

REG2 linear voltage regulator

REG2 is a linear voltage regulator (

Figure 7.) with a dedicated supply pin VIN. The output

voltage (between 1.5V and 3.3V) is fixed by an external divider. It can be turned on/off by

SPI. It has a current protection which limits the maximum allowable output current.

2.5

High side drivers

Two high-side driver (

Figure 10.) with charge pump controlled by SPI are available inside

L5953. They are protected against short to ground: the short circuit protection limits the

maximum output current.

A diagnostic procedure is available to detect open load, short to battery and overcurrent.

Open load and short to battery can be reveal only in test mode while overcurrent is active

only during normal operation of the device. (see

4.2 on page 18)