AS3909 datasheet(14/77 Pages) AMSCO

14 / 77 page

AS3909/AS3910 – 14

ams Datasheet, Confidential: 2013-Oct [3-02]

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

Operating Modes

The AS3909/10 operating mode is defined by the content of the

Operation Control Register (address #01).

At power up, all bits of the Operation Control Register are set to

0 and the AS3909/10 is in Power-down mode. In this mode –

the AFE static power consumption is minimized, only the POR

and part of bias are active, regulators are transparent and are

not operating. The SPI is still functional in this mode; so all

settings of ISO mode definition and configuration registers can

be done.

Control bit en (bit 7 of Operation Control Register) is controlling

both the oscillator and regulators. When this bit is set, the

device enters in Ready mode. In this mode, the oscillator and

regulators are enabled. An interrupt is sent to inform the

microcontroller when the oscillator frequency is stable.

Another possibility to enter in Ready mode is to assert EN pin

high (logic OR function between bit en and pin EN).

Enable of Receiver and Transmitter are separated, so it is

possible to operate one without switching on the other (control

bits rx_en and tx_en). In some cases this may be useful, in case

the reader field has to be maintained and there is no

transponder response expected receiver can be switched-off to

save current. Another example is NFCIP target mode in which

RF field is generated by the initiator and only Receiver operates.

The receiver also has a low power mode in which its power

consumption and as consequence sensitivity are reduced. This

mode is entered in by setting control bit rx_lp.

The last control bit of the Operation Control Register is nfc_t bit.

Setting of this bit is only allowed in case the NFC mode is set in

the ISO mode definition register. Setting this bit to one, while all

other Operation Control Register bits are set to 0, puts the

AS3909/10 into Initial NFC Target mode. In this low power

mode, only the Target Activation Detector, which will detect a

presence of external RF field, is active. Once the presence of

external RF field is detected, an interrupt is sent to

microcontroller which will in turn switch on oscillator and

receiver.

Transmitter

The Transmitter contains two identical driver blocks which are

driving external antenna connected to pins RFO1 and RFO2. The

driver is composed of 8 segments having binary weighted

output resistance. The MSB segment typical ON resistance is 3Ω;

when all segments are turned on, the output resistance is

typically 1.5Ω. Usually certain segments are switched off to

define AM modulated level, while they are all turned on to

define the non-modulated level. It is also possible to switch off

Application Information

AS3909 数据表(PDF) 14 Page - ams AG

AS3909 数据表(HTML) 14 Page - ams AG

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