L5953

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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.

Low Voltage Warning(Figure 7)

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

If S1 pin voltage is higher than Vst, the output 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.

REG2 Linear Voltage Regulator (Figure 5)

REG2 is a linear voltage regulator 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.

High Side Drivers (Figure 8)

Two high-side driver with charge pump controlled by SPI are available inside L5953. They are protected against

short to ground: the short circuit potection 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

operationof the device. (see OPERATION -page 13

PWM Step Down Voltage Regulator (Figure 9)

The switching regulator inside the L5953 is a voltage control mode (also known as "direct duty cycle") Buck reg-

ulator: the error signal coming from the error amplifier is compared with a sawtooth to set on and off times of the

power switch.

The feedforward control is introduced to get a quickly response to input voltage changes: the sawtooh has a

fixed frequency and an amplitude variable with the battery voltage.

Continuous mode operation is recommended in order to reduce the stress of the output capacitor and of the

free-wheeling diode.

Error amplifier and compensation network

The error amplifier (EA) is a voltage amplifier whose non-inverting input is fixed to the reference voltage (1.275V

bandgap voltage) and whose inverting input and output are externally available for feedback and frequency

compensation.