Direct Connection to a Microcontroller Configuration

MC33690 Standalone Tag Reader Circuit, Rev. 5

Freescale Semiconductor

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9

Direct Connection to a Microcontroller Configuration

When a high level is applied on MODE1, the circuit is in configuration C (see Figure 26). The demodulated data are sent

through DOUT.

The AM pin is set as a VDD referenced input pin receiving the AM command. Forcing high and low levels on AM achieves the

amplitude modulation by switching on/off both antenna drivers. Meanwhile, this amplitude modulation can be monitored on

DOUT. This allows antenna short and open circuit diagnosis.

The circuit can be put into standby mode by applying a low level on the MODE2 pin. In standby mode, the oscillator and most

of the internal biasing currents are switched off. Therefore, the functions (tag reader and ISO 9141 interface) are inactive except

for the voltage regulator. The driver outputs TD1 and TD2 are frozen in their state (high or low level) before entering into

standby mode. DOUT forces a low level.

The ISO 9141 interface K is standalone and can be directly controlled by the input pin Tx and monitored by the output Rx.

Applying a logic high level on Tx switches the output driver K on (dominant zero state when an external pull-up resistor is

connected between K and VBAT). Applying a logic low level turns the driver off (one recessive state).

Rx monitors the voltage at the K pin. When the voltage is below the low threshold voltage, Rx forces a logic low level. When

the voltage is above the high threshold voltage, Rx forces a logic high level.

In standby mode, Tx is disabled and Rx output monitors the voltage at the K pin.

Figure 10. Configuration C State Diagram

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Electrical Characteristics

Typical values reflect average measurements at VSUP=12V and TJ=25°C.

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Supply Current

Typical values reflect average measurements at 6V

≤ V

SUP ≤ 16V, VSS = 0V, TJ = –40°C to +125°C, unless otherwise noted.

TD1/2 off

Standby

Wake-up

mode2 low

mode2 high

mode2 low

TD1/2

AM high

AM high

AM low

Reset

AM low

switching