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P21XXCSR-EVB

Powerharvester® Chipset Reference Design Evaluation Board

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P21XXCSR-EVB

P21XX Powerharvester® Chipset Reference Design

Evaluation Board

Typical Operation

The harvester circuit converts RF energy within the appropriate frequency band into DC power. This is

monitored by one of three voltage detectors. The user selects 1.2V, 0.9V or 0.7V as the threshold

voltage via JP3, JP4 or JP5 respectively. The storage capacitor, selected via JP1, then charges up to the

selected threshold voltage. When VCAP reaches its maximum value (VMAX), INT is set high, the boost

converter turns on, and VOUT is set to the output voltage selected via S1. The storage capacitor then

discharges until VCAP reaches its minimum value (VMIN) and then sets INT low, shutting off the boost

converter until VCAP charges back up to its maximum value.

RSSI Operation (DOUT, DSET)

The RSSI functionality allows the sampling of the received signal to provide an indication of the amount

of energy being harvested. When DSET is driven high the harvested DC power will be directed to a

resistor, and the corresponding voltage will be provided to DOUT. The voltage on DOUT can be read after

a 50μs settling time. When the RSSI functionality is being used, the harvested DC power is not being

stored. If the RSSI functionality is not used, DOUT and DSET should be left unconnected. DSET has an on-

board pull down.

Reset (RESET)

The RESET function allows the voltage from VOUT to be turned off before the storage capacitor reaches

the lower threshold, VMIN, thereby saving energy and improving the recharge time back to the

activation threshold, VMAX. The RESET function can be implemented by a microcontroller. When the

function of the microcontroller is completed, driving RESET high will disable the voltage from VOUT.

Care should be taken to ensure that the microcontroller, especially during power-on, does not

inadvertently drive RESET high. This will immediately shutdown the output voltage. If the RESET

functionality is not used, RESET should be left unconnected.

Interrupt (INT)

The interrupt function provides a digital indication that voltage is present at the VOUT pin. INT can be

used in more sophisticated systems that contain other storage elements and can be used as an

external interrupt to bring a device such as microcontroller out of a deep sleep mode. The digital high

level of the INT pin will be between VMIN and VMAX. The INT pin can provide a maximum of 0.1mA of

current. If the INT functionality is not used, INT should be left unconnected.

Selecting Turn-On Voltage

JP3, JP4 and JP5 are used to select the capacitor voltage at which the boost converter will turn on. Each

is a four pin header, and the two two-pin jumpers are moved to the header corresponding to the

desired threshold voltage. JP3 sets the threshold to 1.2 V, JP4 sets the threshold to 0.9 V, and JP5 sets

the threshold to 0.7 V.

P21XXCSR-EVB v1.0 – 2014/7

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