There are a number of advantages and potential benefits of LIN (LIN-CP, as defined in the SAE J3068 series and ISO 61851-1 Annex D) over traditional control pilot controls (PWM-CP, as defined in SAE J1772 and ISO 61851-1 Annex A), but one that has, thus far, gone under exploited, is the ability for communications with things beyond the vehicle (EV) and the supply equipment (EVSE) on the control pilot (CP) wire. There are many situations where it might be valuable to communicate with something other than supply equipment connected to a vehicle’s inlet or something connected between the vehicle and supply equipment, such as an adapter. Most of the time however, these advantages do not outweigh the inconvenience of requiring a separate source of power, such as a battery, in the accessory. As such, it is necessary to harvest power from either the CP or proximity circuits. While it is, in principal, possible to harvest quite a bit of power from the CP circuit, this cannot be done without affecting the analog levels of the CP circuit required for safety.
Proximity-powered accessories can be divided into two categories: actively-powered and passively-powered. Actively-powered nodes and their potential use cases are described in SAE J3068/2. In short, in cases where the normal functionality of the proximity circuit can be substituted by some other method, and it can be reasonably assumed that it is safe to do so, proximity is driven to a current-limited 12 V. Passively-powered nodes as described here are backwards-compatible with equipment designed for PWM-CP. Passive nodes are most valuable with EV cable assemblies and inlet adapters; other EV accessories generally require more power than is available in the traditional proximity circuit and require richer communications than are possible with exclusively PWM-CP anyway.
In this context, what are the advantages of an additional LIN node in the EV cable assembly or adapter?
- Support for voltages above 480/277 VAC and currents above 63/70A
- Support for currents without associated coding resistors, e.g., 48 A with the SAE J3068 connector
- Monitoring of temperatures to improve foldback behavior and reliability
- Reporting of cable or adapter type to detect potentially incompatible or unsafe configurations.
How can LIN nodes be passively powered by the standard proximity circuit?
The relevant standards* (SAE J3068, SAE J1772, and SAE J3400) require, on both the inlet and the socket-outlet, that the proximity circuit consist of a 330 Ω resistor (R4/RA) pulled up to a regulated 5 V, and the voltage is monitored to determine the cable ampacity and/or latch state as appropriate. Additionally, the vehicle inlet is required to have a 2.7 kΩ resistor-to-ground (R5), but this only has the effect of slightly lowering the expected voltage.
* Unfortunately, ISO 61851-1 does not define the proximity detection circuits in such a way where cable nodes can draw their power from the circuit. The relevant values (The pullup resistor R4/RA and the voltage to which it is pulled up) are only recommendations where they are specified and are only specified for Type 1. The 2.7 kΩ pull-down (R5) is only mentioned for Type 1, where it is only a recommendation, but is present in many existing type 2 implementations. Some Type 2 inlets are equipped with other resistor values (such a 4.7kΩ which could be used to differentiate Type-1/Type-2 harnesses) when unplugged.
| Nominal Ω (Plug or Connector) | SAE Universal Socket-outlet Status | J3068 Inlet Status | J3400 (J1772) Inlet Status | Nominal Voltage at Socket-Outlet | Nominal Voltage at Inlet |
|---|---|---|---|---|---|
| 1500 Ω | 13 A | 13A/ DC charging | – | 4.10 V | 3.73 V |
| 680 Ω | 20 A | 20 A | – | 3.37 V | 3.11 V |
| 480 Ω | 0 A | J1772 Unlatched (0A) | J1772 Unlatched (0A) | 2.96 V | 2.76 V |
| 220 Ω | 32 A | 32 A | – | 2.00 V | 1.91 V |
| 150 Ω | 48 A | J1772 or J3400 Connector Inserted | Connector Inserted | 1.56 V | 1.51 V |
| 100 Ω | 63/70 A | 63/70 A | – | 1.16 V | 1.13 V |
Credit: Rohitbd via wikipedia.org)
A simple shunt regulator using a programmable Zener produces exactly this result while allowing nearly all of the available power to be used by the remaining circuitry. The two largest limitations are: available power, and availability of a suitable programmable Zener that can operate below the 1.2 V produced by a standard silicon bandgap reference. Availability of microcontrollers capable of operating below 1.8 V is also a limitation. Power (disregarding the 2.7 kΩ parallel resistor) is maximized where the (equivalent) load resistance equals the source resistance, i.e., 330 Ω, yielding 2.5 V.
Power is not substantially less at the 1.91-2 V of 32 A, it is above both the 1.2 V and 1.8 V thresholds and is (at least arguably), the most important value, making it the ideal starting point. Both states associated with SAE J1772/3400 are also reasonably possible. 63/70 A is likely to prove more difficult as it is below both voltage thresholds, but a reasonable amount of power is still available.
A proof-of-concept 32 A LIN cable node has therefore been designed and tested in both plug and connector configurations.
The operation is as follows: A TLVH431 is used as the shunt regulator. A Freescale MC9S08QL8CTJ is used as the microcontroller. A 4X charge pump is made with discrete Schottky diodes and a PWM output from the microcontroller to produce ~6.4-6.7 V for the LIN transceiver. The LIN transceiver is a Microchip MCP2003B, chosen for its very low power consumption, and minimal loading (~900 KΩ) of the CP line when depowered. PWM-CP is detected by looking for any signal on the CP line below ~-7 V and disabling the charge pump for ~1.5 ms. The CP line is sampled through a 2 MΩ resistor to minimize additional loading on the -12 V of the PWM-CP waveform. With this configuration, the LIN transceiver voltage dips to just over 5 V when transmitting, which is outside the recommended 6-7 V, but is not as critical when transmitting as receiving.
Results: Effect on PWM-CP is indeed minimal
