ST25R3916 datasheet(42/157 Pages) STMICROELECTRONICS

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Application information

ST25R3916/7

42/157

DS12484 Rev 4

3.3 V supply mode is set this block is disabled, its output is connected to VDD through a

1kΩ resistor.

Typical consumption of Power-down support block is 600 nA at 5 V supply.

Measurement of supply voltages

Using direct command Measure power supply it is possible to measure VDD and regulated

voltages VDD_A, VDD_D and VDD_RF.

4.2.12

Overshoot / undershoot protection

The overshoot / undershoot protection mechanism makes it possible to control the

transmitting waveform during challenging test conditions. This is accomplished by setting bit

patterns in the corresponding registers that produce additional signals during the transition

phase from modulated to unmodulated state or vice versa.

The operation of this protection is explained by using the overshoot registers. The overshoot

mechanism is only effective when bits are written in ov_pattern<13:0>. Setting

ov_pattern<13:0> to 0 implicitly disables the overshoot protection, as the configuration from

Mode definition register and TX driver register is applied for all clock cycles after the

transition.

The overshoot mode has to be set in control bits ov_tx_mode<1:0> and defines the drive

level for the complete bit pattern. Three modes are available.



ov_tx_mode<1:0> = 00b: the transmitter outputs are driven with VDD_DR when the

respective ov_pattern bit is 1.



ov_tx_mode<1:0> = 01b: the transmitter outputs are driven with VDD_AM when the

respective ov_pattern bit is 1.



ov_tx_mode<1:0> = 10b: the transmitter outputs are stopped (like Type A pause) when

the respective ov_pattern bit is 1.

The overshoot protection pattern ov_pattern<13:0> is applied LSB first. For the first 14 clock

cycles after the transition from modulated to unmodulated state, each of the 14 bits of the

overshoot protection pattern specifies the driver configuration to apply. So ov_pattern<0>

defines which driver configuration to apply for the first clock cycle after the transition from

modulated to unmodulated state, and ov_pattern<9> defines which driver configuration to

apply for the tenth clock cycle after the transition from modulated to unmodulated state.

From the 15th clock cycle on the settings from TX driver register are used.

The undershoot protection works in a similar manner for transitions from unmodulated state

of the carrier to modulated state of the carrier.

4.2.13

Reader operation

The Ready mode has to be entered by setting the bit en of the Operation control register. In

this mode the oscillator is started and the regulators are enabled. When the oscillator

operation is stable an interrupt is sent and bit osc_ok indicates it.

The operation mode and data rate must be then configured by writing the Mode definition

related to operation mode have to be defined too. If the selected operation mode uses AM

modulation for communication reader to tag the modulation depth must be configured.

Before sending any command to a transponder the transmitter and receiver have to be

enabled by setting the bits rx_en and tx_en. Several NFC standards define a guard time

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