A5975AD datasheet(11/50 Pages) STMICROELECTRONICS

11 / 50 page

A5975AD

Functional description

Doc ID 018761 Rev 1

11/50

Functional description

The main internal blocks are shown in the device block diagram in Figure 3. They are:

●

A voltage regulator supplying the internal circuitry. From this regulator, a 3.3 V

reference voltage is externally available.

●

A voltage monitor circuit which checks the input and the internal voltages.

●

A fully integrated sawtooth oscillator with a frequency of 500 kHz

± 15%, including also

the voltage feed-forward function and an input/output synchronization pin.

●

Two embedded current limitation circuits which control the current that flows through

the power switch. The pulse-by-pulse current limit forces the power switch off cycle-by-

cycle if the current reaches an internal threshold, while the frequency shifter reduces

the switching frequency in order to significantly reduce the duty cycle.

●

A transconductance error amplifier.

●

A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to

drive the internal power.

●

A high side driver for the internal P-MOS switch.

●

An inhibit block for standby operation.

●

A circuit to implement the thermal protection function.

Figure 3.

Block diagram

A5975AD Datasheet(PDF) 11 Page - STMicroelectronics