AS3911 datasheet(37/149 Pages) AMSCO

37 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 37

Appl icatio n I n f o rm a t i o n

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.

Serial Peripheral Interface (SPI)

While signal /SS is high the SPI interface is in reset, while it is

low the SPI interface is enabled. It is recommended to keep

signal /SS high whenever the SPI interface is not in use. MOSI is

sampled at the falling edge of SCLK. All communication is done

in blocks of 8 bits (bytes). First two bits of first byte transmitted

after high to low transition of /SS define SPI operation mode.

MSB bit is always transmitted first (valid for address and data).

Read and Write modes support address auto-incrementing,

which means that in case after the address and first data byte

some additional data bytes are sent (read), they are written to

(read from) addresses incremented by ‘1’. Figure 22 defines

possible modes.

MISO output is usually in tristate, it is only driven when output

data is available. Due to this the MOSI and the MISO can be

externally shorted to create a bidirectional signal.

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