PoDL system with active dV/dt and dI/dt control
A Power Over Data Lines (PoDL) system includes Power Sourcing Equipment (PSE) supplying DC power and differential Ethernet data over a single twisted wire pair to a Powered Device (PD). Due to start-up perturbations, PD load current variations, and other causes, dV/dt noise is introduced in the power signal. Such noise may be misinterpreted as data unless mitigated somehow. Rather than increasing the values of the passive filtering components conventionally used for decoupling/coupling the power and data from/to the wire pair, active circuitry is provided in the PSE, PD, or both to limit dV/dt in the power signal. Such circuitry may be implemented on the same chip as the PSE controller or PD controller. Therefore, the sizes of the passive components in the decoupling/coupling networks may be reduced.
1. A Power over Data Lines (PoDL) system, which enables power and differential data transmission over a single wire pair, comprising:
a passive coupling network in Power Sourcing Equipment (PSE) coupled to the wire pair for coupling a DC power signal and differential data to the wire pair;
a passive decoupling network in a Powered Device (PD) coupled to the wire pair for decoupling the DC power signal and differential data from the wire pair;
a PD load powered by the DC power signal; and
dV/dt limiting circuitry, separate from the passive coupling network and the passive decoupling network, comprising one or more active components, wherein the dV/dt limiting circuitry limits dV/dt in the power signal, the dV/dt limiting circuitry being configured to limit the dV/dt of the DC power signal at all currents drawn by the load.
2. The system of claim 1 wherein the dV/dt limiting circuitry comprises:
a transistor in series with a power signal line in the PSE; and
a control circuit in the PSE responsive to dV/dt on the power signal line, wherein the control circuit controls a conductivity of the transistors in response to the dV/dt such that the dV/dt is limited.
3. The system of claim 2 wherein the control circuit comprises a capacitor having a first terminal coupled to the power signal line and a second terminal coupled to a control terminal of the transistor.
4. The system of claim 3 further comprising a current source supplying current to the control terminal of the transistor, wherein the capacitor diverts current from the current source to limit the dV/dt.
5. The system of claim 1 wherein the PD includes a DC-DC converter for converting incoming PoDL voltage to a target voltage for the PD load, wherein the dV/dt limiting circuitry comprises:
a duty cycle slew rate limiting circuit coupled to the DC-DC converter for limiting a slew rate of the duty cycle of the converter in response to changes in PD load current, thus reducing a dl/dt into the PD load, resulting in a reduced dV/dt in the power signal.
6. The system of claim 5 wherein the duty cycle slew rate limiting circuit comprises:
a differentiator circuit that outputs a first signal proportional to dV/dt in the power signal; and
a DC-DC converter controller circuit that receives a first feedback signal corresponding to an output voltage of the converter and regulates the output voltage to be a target voltage,
wherein the first signal is provided to the converter controller to limit the dV/dt to a maximum value by limiting the slew rate of the duty cycle of the converter in response to changes in the PD load.
7. The system of claim 5 wherein the duty cycle slew rate limiting circuit comprises:
a slew rate limited differential amplifier, wherein the slew rate limited differential amplifier outputs a control signal in the converter that controls the duty cycle.
8. The system of claim 7 comprises a second differential amplifier receiving a voltage corresponding to an output voltage of the converter and receiving a reference voltage, wherein an output of the second differential amplifier is coupled to an input of the slew rate limited differential amplifier.
9. The system of claim 8 wherein the slew rate limited differential amplifier comprises a capacitor coupled to its output, where the output is coupled to an input of the slew rate limited differential amplifier.
10. The system of claim 1 wherein the dV/dt limiting circuitry limits dI/dt into the PD load.
11. The system of claim 1 wherein the passive coupling network and the passive decoupling network comprises:
inductors for passing the power signal but blocking the differential data; and
capacitors for passing the differential data but blocking the power signal.
12. The system of claim 1 wherein the DC power signal is generated by a voltage source in the PSE.
13. The system of claim 1 wherein the differential data comprises Ethernet data.
14. The system of claim 1 wherein the dV/dt limiting circuitry comprises d 2 I/dt 2 limiting circuitry in the PD that limits PD load current variations.
15. A Power over Data Lines (PoDL) system, which enables power and differential data transmission over a single wire pair, comprising:
a passive coupling network in Power Sourcing Equipment (PSE) coupled to the wire pair for coupling a DC power signal and differential data to the wire pair;
a passive decoupling network in a Powered Device (PD) coupled to the wire pair for decoupling the DC power signal and differential data from the wire pair;
a PD load powered by the DC power signal; and
d 2 I/dt 2 limiting circuitry, separate from the passive coupling network and the passive decoupling network, comprising one or more active components, wherein the d 2 I/dt 2 limiting circuitry limits dV/dt in the DC power signal, the d 2 I/dt 2 limiting circuitry being configured to limit the dV/dt in the DC power signal at all currents drawn by the load.
16. The system of claim 15 wherein the PD includes a DC-DC converter for converting incoming PoDL voltage to a target voltage for the PD load, wherein the d 2 I/dt 2 limiting circuitry comprises:
a duty cycle slew rate limiting circuit coupled to the DC-DC converter for limiting a slew rate of the duty cycle of the converter in response to changes in PD load current, thus reducing a dI/dt into the PD load, resulting in a reduced dV/dt in the power signal.
17. The system of claim 16 wherein the duty cycle slew rate limiting circuit comprises:
a differentiator circuit that outputs a first signal proportional to dV/dt in the power signal; and
a DC-DC converter controller circuit that receives a first feedback signal corresponding to an output voltage of the converter and regulates the output voltage to be a target voltage,
wherein the first signal is provided to the converter controller to limit the d 2 I/dt 2 to a maximum value by limiting the slew rate of the duty cycle of the converter in response to changes in the PD load.
18. The system of claim 16 wherein the duty cycle slew rate limiting circuit comprises:
a slew rate limited differential amplifier, wherein the slew rate limited differential amplifier outputs a control signal in the converter that controls the duty cycle.
19. The system of claim 18 wherein the slew rate limited differential amplifier comprises a capacitor coupled to its output, where the output is coupled to an input of the slew rate limited differential amplifier.
20. The system of claim 15 wherein the d 2 I/dt 2 limiting circuitry limits dI/dt into the PD load.