Specifications

Chapter 5 – Power Supplies for PL Smart Transceivers
156 PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Boo
k
Energy Storage Power Supplies
PL Smart Transceivers incorporate a power management feature that supports the design of low cost power supplies
in cost sensitive consumer applications such as networked light dimmers, switches, and household appliances. This
class of application typically requires only occasional low-duty cycle transmission from the device. Power supplies
for these devices can take advantage of the very low receive current and wide V
A
supply range of the PL Smart
Transceiver to charge a capacitor during receive mode, and then use the energy stored on the capacitor for
transmission. By using an energy storage system, the device can use a smaller, less expensive, power supply than a
device with an equivalent “full power” supply. In this way, a low-current supply can be used which only has to
supply the required receive mode current, plus an incremental current to recharge a capacitor between transmissions.
An energy storage power supply is generally designed so that its V
A
supply voltage, while in receive mode, is above
the 12V nominal specification (e.g., 15V). During packet transmission the voltage on the V
A
supply is then allowed
to drop as energy from the capacitor is used for transmission. The value of the energy storage capacitor must be large
enough so that the V
A
supply voltage is still sufficient for proper operation after transmitting a single maximum-
length packet. Proper device operation is then maintained when the energy storage capacitor is selected such that the
V
A
power supply meets both of the following conditions:
• V
A
≥10.8V after the typical I
A
transmit load of 120mA has been active for 92.2ms for a C-band device
(140.7ms for an A-band device). This condition only needs to be met at room temperature with nominal AC
line voltage (see footnote below regarding derivation of transmission times).
• V
A
≥8.5V after the worst case IA transmit load of 250mA has been active for 92.2ms for a C-band device
(140.7ms for an A-band device). For proper node operation this condition must be met over the full range of
worst-case component tolerances (including I
DD5
drain), AC line voltage, and temperature (see footnote
below regarding derivation of transmission times).
Having chosen a storage capacitor to provide adequate voltage after transmitting a single packet, the power
management feature of the PL Smart Transceiver must also be enabled to ensure adequate supply voltage over the
span of multiple packet transmissions. The power management feature prevents excessive power supply droop from
transmission of multiple back-to-back packets under worst case conditions by monitoring the voltage on the energy
storage capacitor and then, if required, regulating the time between transmissions so that the capacitor has time to
recharge.
The power management feature is enabled by first connecting an appropriate resistive voltage divider between the
V
A
supply and the OOGAS pin of PL Smart Transceiver IC, as shown in reference schematic diagrams described in
Appendix A. In addition, use of a standard transceiver type with a “-LOW” suffix is required to enable the power
management feature, as described in Chapter 8, PL Smart Transceiver Programming.
Note: For the primary carrier frequency, a 32 byte packet (without preamble but including CRC) corresponds to a maximum
transmission duration of 74.6ms for a C-band device and 113.8ms for an A-band device. Calculating the maximum transmission
duration for a packet at the secondary carrier frequency is somewhat more complicated due to the combination of error
correction and data compression used with that carrier frequency. If we consider a case where message traffic satisfies the 32
byte packet length condition plus three further common conditions, then the maximum transmission duration can be calculated
to be 92.2ms for a C-band device (140.7ms for an A-band device). This maximum duration is applicable for applications where:
1) there are no priority packet transmissions from the energy storage device; 2) subnet and node numbers are in the range 0
through 15; and 3) if a six byte domain is used, it is assigned to be equal to a Neuron core ID number. For applications which do
not meet the conditions listed in this note, contact Echelon Lon Support for maximum packet length calculations.