This article describes how to configure PN5180 LPCD using NXP Cockpit Tool and using NXP NFC Reader library.
1 PN5190 LPCD Overview
PN5180 LPCD operates in two modes: auto calibration mode and self-calibration mode.
Auto calibration mode: everything done automatically
Self-calibration mode: calibration must be done manually before starting the LPCD.
1.1 Auto Calibration Mode ( 00b)
The LPCD calibration is done automatically when the LPCD is started, using the gear and threshold as defined in the EEPROM. This mode always uses the same gear for the LPCD, and is the fast and easiest way to start the LPCD. It is recommended to choose a gear, which always keeps the ITVDD and field strength limits, so normally, the highest gear number.
Auto calibration mode is most commonly used, it is a standard use case.
Below parameters need to be configured correctly in EEPROM
- LPCD_REFERENCE_VALUE
- LPCD_REFVAL_GPO_CONTROL
- LPCD_THRESHHOLD ( 0x37)
- LPCD wakes up, if current AGC during “ping” > AGC Reference + LPCD_THRESHOLD or< AGC Reference -LPCD_THRESHOLD
- Minimum LPCD_THRESHOLD = 03…08 (very sensitive)
- Maximum LPCD_THRESHOLD = 40 … 50 (very robust)
- LPCD_FIELD_ON_TIME (0x36)
- RF on time in 8µs, excluding the fix time . Fix time = 62µs
- 01 => RF on = 70µs
- 02 => RF on = 78µs
- 03 => RF on = 86µs
- 10 => RF on = 190µs
1.2 Self Calibration Mode (01b)
The LPCD calibration must be manually triggered, with reading or writing into the AGCREF_CONFIG register.
Reading from this register - without prior writing - starts an LPCD calibration. The
calibration is executed using the gear which is resulting from the actual DPC setting under the actual antenna detuning condition. AGC_GEAR is used in the LPCD self-calibration.
Reading from this register - without prior writing - delivers in addition to the AGC_GEAR
value the AGC_VALUE. The AGC_VALUE is used in the LPCD self-calibration.
Writing to this register:
Writing data to this register is required before starting the LPCD in Self-calibration mode.
Either the previously read AGC_GEAR or a user-defined gear can be chosen. The
previously read AGC_VALUE has to be written in any case.
Writing data to this register defines the values for AGC_GEAR without taking the
actual detuning condition into account. The value of AGC_GEAR to perform an LPCD
calibration which derives the AGC_VALUE. This AGC_VALUE and the AGC_GEAR are
used in the LPCD self-calibration.
Self-calibration mode always requires a Read AGC_REF_CONFIG, followed by a write
AGC_REF_CONFIG, using the previously read AGC_VALUE.
The LPCD calibration can be done in two different options:
Option 1: Read AGC_REF_CONFIG register: This command executes a standard RF Field on. So depending on the load condition the DPC adjusts the output power. The final gear is take as gear for the LPCD. This option guarantees that the maximum output power is taken for the LPCD.
Option 2: Write AGC_REF_CONFIG register: This command executes a LPCD calibration ping with the gear number, as defined in the AGC_REF_CONFIG, bit 10:13. This option allows a flexible use of any of the defined gears for the LPCD.
PN5180 LPCD self-calibrate is executed, using
- Gear -> AGC_REF_CONFIG (Register)
- Threshold -> LPCD_THRESHOLD (EEPROM)
- RF on time-> LPCD_FIELD_ON_TIME (EEPROM)
2 How to configure PN5180 LPCD with Cockpit
The NFC Cockpit allows the configuration and test of the low power card detection of the PN5180 as shown in below picture. The LPCD parameter, which are stored in the EEPROM, can be changed and the LPCD can be started. The LPCD tab allows to directly define and write the related EEPROM addresses:
LPCD Gear #: Defines the gear number, which is used for the LPCD in auto calibration mode, stored in addr. 0x34, bit 0:3
Threshold Value: Defines the threshold window, As soon as the AGC value during the LPCD ping exceeds the AGC reference value + threshold window, the IRQ will be raised and the PN5180 wakes up.
Field On Time: Defines the ping length
Standby time : This value defines the time between two pings in ms.
FieldOn Current: This value is ITVDD under the loading condition, when RF field is on with the used gear. This value does not have any influence on the LPCD execution, but simply is used to estimate the overall average current consumption. This current estimation is calculated, when the LPCD is started.
3 How to configure PN5180 LPCD with NXP NFC reader library.
The LPCD works in two phases:
First the standby phase is controlled by the wake-up counter (timing defined in the
instruction), which defines the duration of the standby of the PN5180.
Second phase is the detection-phase. The RF field is switched on for a defined time
(EEPROM configuration) and then the AGC value is compared to a reference value.
Below is the flow chart for PN5180 LPCD
