AS3911 datasheet(36/149 Pages) AMSCO

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AS3911 – 36

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

A p pl i c at io n I n f o r m at i o n

supply mode the adjustment range is from 2.4V to 3.4V

with steps of 100mV. Default regulated voltage is the

maximum one (5.1V and 3.4V in case of 5V and 3.3V supply

mode respectively).

• Regulator and Timer Display Register is a read only register

which displays actual regulated voltage when regulator is

operating. It is especially useful in case of automatic mode,

since the actual regulated voltage, which is result of direct

command Adjust Regulators, can be observed.

The VSP_RF regulator also includes a current limiter which limits

the regulator current to 300mArms in normal operation (500mA

in case of short). In case the Transmitter output current higher

the 300mArms is required VSP_RF regulator cannot be used to

supply the Transmitter, VSP_RF has to be externally connected

to VDD (connection of VSP_RF to supply voltage higher than VDD

is not allowed).

The voltage drop of the Transmitter current is the main source

of the AS3911 power dissipation. This voltage drop is composed

of drop in the Transmitter driver and in the drop on VSP_RF

regulator. Due to this it is recommended to set regulated

voltage using direct command Adjust Regulators. It results in

good power supply rejection ration with relatively low

dissipated power due to regulator voltage drop.

In Power-down mode the VSP_RF regulator is not operating.

VSP_RF pin is connected to VDD through 1 kΩ resistor.

Connection through resistors assures smooth power-up of the

system and a smooth transition from Power-down mode to

other operating modes.

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.

AS3911 Datasheet(PDF) 36 Page - ams AG

AS3911 Datasheet(HTML) 36 Page - ams AG

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