AS3911 datasheet(38/159 Pages) AMSCO

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AS3911 − Application Information

VSP_A and VSP_D Regulators

VSP_A and VSP_D regulators are used to supply the AS3911

analog and digital blocks respectively. In 3.3 V mode, VSP_A and

VSP_D regulator are set to the same regulated voltage as the

VSP_RF regulator, in 5 V mode VSP_A and VSP_D regulated

voltage is fixed to 3.4 V.

The use of VSP_A and VSP_D regulators is obligatory in 5 V mode

since analog and digital blocks supplied with these two pins

contain low voltage transistors which support maximum supply

voltage of 3.6 V. In 3.3 supply mode the use of regulators is

strongly recommended in order to improve PSRR of analog

processing.

For low cost applications it is possible to disable the VSP_D

regulator and to supply digital blocks through external short

between VSP_A and VSP_D (configuration bit vspd_off in the IO

Configuration Register 2). In case VSD_D regulator is disabled

VSP_D can alternatively be supplied from VDD (in 3.3 V mode

only) in case VSP_A is not more than 300mV lower than VDD.

Power-Down Support Block

In the Power-down mode the regulators are disabled in order

to save current. In this mode a low power Power-down Support

block which maintains the VSP_D and VSP_A in below 3.6V is

enabled. Typical regulated voltage in this mode is 3.1V at 5V

supply and 2.2V at 3V supply. When 3.3 V supply mode is set

the Power-down Support block is disabled, its output is

connected to VDD through 1kΩ resistor.

Typical consumption of Power-down Support block is 600nA at

5V supply.

Measurement of Supply Voltages

Using direct command Measure Power Supply it is possible to

measure VDD and regulated voltages VSP_A, VSP_D, and

VSP_RF.

Communication to External Microcontroller

The AS3911 is a slave device and the external microcontroller

initiates all communication. Communication is performed by a

4-wire Serial Peripheral Interface (SPI). The AS3911 asks

microcontroller for its attention by sending an interrupt (pin

IRQ). In addition, the microcontroller can use clock signal

available on pin MCU_CLK when the oscillator is running.

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