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SLOS758G – DECEMBER 2011 – REVISED MARCH 2020
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Detailed Description
Copyright © 2011–2020, Texas Instruments Incorporated
The input pin EN2 has two functions:
•
A direct connection from EN2 to VIN to ensure the availability of the regulated supply VDD_X and an
auxiliary clock signal (60 kHz, SYS_CLK) for an external MCU. This mode (EN = 0, EN2 = 1) is
intended for systems in which the MCU is also being supplied by the reader supply regulator (VDD_X)
and the MCU clock is supplied by the SYS_CLK output of the reader. This lets the MCU supply and
clock be available during sleep mode.
•
EN2 enables the start-up of the reader system from complete power down (EN = 0, EN2 = 0). In this
case, the EN input is being controlled by the MCU (or other system device) that is without supply
voltage during complete power down (thus unable to control the EN input). A rising edge applied to the
EN2 input (which has an approximately 1-V threshold level) starts the reader supply system and
13.56
‑
MHz oscillator (identical to condition EN = 1).
When the user MCU controls EN and EN2, use a delay of 5 ms between EN and EN2. When the MCU
controls only EN, TI recommends connecting EN2 to either VIN or GND, depending on the application
MCU requirements for VDD_X and SYS_CLK.
NOTE
Using EN = 1 and EN2 = 1 in parallel at start-up should not be done as it may cause
incorrect operation.
This start-up mode lasts until all of the regulators have settled and the 13.56-MHz oscillator has stabilized.
If the EN input is set high (EN = 1) by the MCU (or other system device), the reader stays active. If the EN
input is not set high (EN = 0) within 100 µs after the SYS_CLK output is switched from auxiliary clock
(60 kHz) to high-frequency clock (derived from the crystal oscillator), the reader system returns to
complete Power-Down Mode 1. This option can be used to wake the reader system from complete power
down (PD Mode 1) by using a push-button switch or by sending a single pulse.
After the reader EN line is high, the other power modes are selected by control bits within the Chip Status
Control register (0x00). The power mode options and states are listed in
When EN is set high (or on rising edge of EN2 and then confirmed by EN = 1) the supply regulators are
activated and the 13.56-MHz oscillator started. When the supplies are settled and the oscillator frequency
is stable, the SYS_CLK output is switched from the auxiliary frequency of 60 kHz to the 13.56-MHz
frequency derived from the crystal oscillator. At this time, the reader is ready to communicate and perform
the required tasks. The MCU can then program the Chip Status Control register 0x00 and select the
operation mode by programming the additional registers.
•
Standby mode (bit 7 = 1 of register 0x00), the reader is capable of recovering to full operation in
100 µs.
•
Mode 1 (active mode with RF output disabled, bit 5 = 0 and bit 1 = 0 of register 0x00) is a low-power
mode that lets the reader recover to full operation within 25 µs.
•
Mode 2 (active mode with only the RF receiver active, bit 1 = 1 of register 0x00) can be used to
measure the external RF field (as described in RSSI measurements paragraph) if reader-to-reader
anticollision is implemented.
•
Mode 3 and Mode 4 (active modes with the entire RF section active, bit 5 = 1 of register 0x00) are the
modes used for typical transmit and receive operations.
