AS3955 datasheet(17/111 Pages) AMSCO

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[v1-01] 2015-Apr-29

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AS3955 − Detailed Description

Figure 16:

Regulated Voltage Output Settings

Silent Mode

The Silent mode enables detection of the power status of a

circuit whose supply (Vdd) is connected to VP_IO pin. If this

mode is enabled and the voltage measured on pin VP_IO is

below the configured threshold value, the RF part of AS3955

will be disabled, and the IC will not be responsive to incoming

commands. Silent mode settings can be performed by using

Configuration Byte IC_CFG0.

This feature overcomes a potentially inconsistent behavior in a

battery powered system, where a passive NFC tag can always

communicate with a NFC device, also in case the battery is not

sufficiently charged to supply the rest of the system. A typical

example is when the NFC tag is used for Bluetooth pairing:

AS3955 would trigger a pairing procedure only in case the

system is fully operational by monitoring the supply voltage.

Memory Protection

AS3955 internal memory can be protected from unauthorized

access by enabling password authentication. A 32-bit password

can be set to protect the full user memory, or part of it, to allow

the creation of a public data and a private data area. Password

protection can be applied for read and write accesses.

Password authentication is performed through a standard

WRITE command to the Authentication Password block. A

maximum of 7 negative attempts are permitted before the chip

is locked. Once authenticated, the user can modify the

password.

Password protection applies to RF communication only.

Further information on how to handle password authentication

can be found in Authentication Password, Configuration Byte

AUTH_CFG, Configuration Byte AUTH_CNT and Configuration

Byte AUTH_LIM.

vreg<4:0>

Output Voltage

Abs. Accuracy

00000b

1.8V

±115mV

00001b

Step 100mV

±20mV

Linearly increasing

over range

11011b

4.5V

±225mV

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