NT3H2211W0FHKH Datasheet, PDF (34/77 Pages) NXP Semiconductors – NTAG I2C plus, NFC Forum Type 2 Tag compliant IC with I2C interface

NXP Semiconductors
NT3H2111/NT3H2211
NFC Forum Type 2 Tag compliant IC with I²C interface
8.5 Watchdog timer
In order to allow the I²C interface to perform all necessary commands (READ, WRITE, ..),
the memory access remains locked to the I²C interface until the register I2C_LOCKED is
cleared by the host - see Table 14.
However, to avoid that the memory stays 'locked' to the I²C for a long period of time, it is
possible to program a watchdog timer to unlock the I²C host from the tag, so that the NFC
device can access the tag after a period of time of inactivity. The host itself will not be
notified of this event directly, but the NS_REG register is updated accordingly (the register
bit I2C_LOCKED will be cleared - see Table 14).
The default value is set to 20 ms (848h), but the watch dog timer can be freely set from
0001h (9.43 s) up to FFFFh (617.995 ms). The timer starts ticking when the
communication between the NTAG I²C and the I²C interface starts. In case the
communication with the I²C is still going on after the watchdog timer expires, the
communication will continue until the communication has completed. Then the status
register I2C_LOCKED will be immediately cleared.
In the case where the communication with the I²C interface has completed before the end
of the timer and the status register I2C_LOCKED was not cleared by the host, it will be
cleared at the end of the watchdog timer.
The watchdog timer is only effective if the VCC pin is powered and will be reset and
stopped if the NTAG I²C is not VCC powered or if the register status I2C_LOCKED is set
to 0 and RF_LOCKED is set to 1.
8.6 Energy harvesting
The NTAG I²C plus provides the capability to supply external low-power devices with
energy harvested from the NFC field of an NFC device as illustrated in Figure 16. All given
values are typical values. For more details refer to Ref. 7.
The voltage and current from the energy harvesting depend on various parameters, such
as the strength of the NFC field, the tag antenna size, or the distance from the NFC
device. NTAG I²C plus provides typically 5 mA at 2 V on the VOUT pin with an NFC
Phone.
Operating NTAG I²C in energy harvesting mode requires a number of precautions:
• A complete total connected capacitor in the range of typically 150 nF up to 220 nF
maximum shall be connected between VOUT and GND close to the terminals to
ensure that the voltage does not drop below VCC min during modulation or during any
application operation.
• Start up load current on VOUT should be limited until sufficient voltage is built on
VOUT.
• If NTAG I²C also powers the I²C bus, then VCC must be connected to VOUT, and
pull-up resistors on the SCL and SDA pins must be sized to control SCL and SDA sink
current when those lines are pulled low by NTAG I²C or the I²C host
• If NTAG I²C also powers the Field Detect bus, then the pull-up resistor on the Field
Detect line must be sized to control the sink current into the Field Detect pin when
NTAG I²C pulls it low
NT3H2111/NT3H2211
Product data sheet
COMPANY PUBLIC
All information provided in this document is subject to legal disclaimers.
Rev. 3.0 — 3 February 2016
359930
© NXP Semiconductors N.V. 2016. All rights reserved.
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