AS3911 datasheet(37/159 Pages) AMSCO

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ams Datasheet

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[v2-11] 2016-Jun-13

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AS3911 − Application Information

VSP_RF Regulator

The intention of this regulator is to improve PSRR of the

Transmitter (the noise of the Transmitter power supply is

emitted and fed back to the Receiver). The VSP_RF regulator

operation is controlled and observed by writing and reading

two regulator registers:

• Regulator Voltage Control Register controls the regulator

mode and regulated voltage. Bit reg_s controls regulator

mode. In case it is set to 0 (default state) the regulated

voltage is set using direct command Adjust Regulators.

When bit reg_s is asserted to 1 regulated voltage is defined

by bits rege_3 to rege_1 of the same register. The regulated

voltage adjustment range depends on the power supply

mode. In case of 5V supply mode the adjustment range is

between 3.9V and 5.1 V in steps of 120 mV, in case of 3.3V

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 200mArms 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.

AS3911 Datasheet(PDF) 37 Page - ams AG

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