STMicroelectronics Evaluation board for A5970AD EVALA5970AD EVALA5970AD Hoja De Datos

DocID14661 Rev 5

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The main internal blocks are shown in the device block diagram in 

. 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.

The internal regulator circuit (shown in 

) consists of a start-up circuit, an internal 

voltage pre-regulator, the bandgap voltage reference and the bias block that provides 
current to all the blocks. The starter supplies the start-up currents to the entire device when 
the input voltage goes high and the device is enabled (inhibit pin connected to ground). The 
pre-regulator block supplies the bandgap cell with a pre-regulated voltage V

REG

 that has 

a very low supply voltage noise sensitivity.