AS3911 datasheet(35/149 Pages) AMSCO

35 / 149 page

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

AS3911 – 35

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

Figure 19:

The AS3911 Power Supply System

Regulators have two basic operation modes depending on

supply voltage, 3.3V supply mode (max 3.6V) and 5V supply

mode (max 5.5V ). The supply mode is set by writing bit sup3V

in the IO Configuration Register 2. Default setting is 5V so this

bit has to be set to one after power-up in case of 3.3V supply.

In 3.3V mode all regulators are set to the same regulated voltage

in range from 2.4V to 3.4V, while in 5V only the VSP_RF can be

set in range from 3.9V to 5.1V, while VSP_A and VSP_D are fixed

to 3.4V.

Figure 19 depicts signals controlling the power supply system.

The regulators are operating when signal en is high (en is

configuration bit in Operation Control Register). When signal

en is low the AS3911 is in low power Power-down mode. In this

mode consumption of the power supply system is also

minimized.

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

Power-down

Support

sup3V

50 ohm

RV<3:0>

VSP_RF

REG

BGR

AGC

AUTOREG

VSP_A

VSP_RF

VSP_D

AGD

reg2Bh

VDD

reg2Ah

VSP_A

REG

VSP_D

REG

adjust

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