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In Host PC that have USB Type C Ports is it correct to assume that they will be implemented with PD controllers and thus :-

  1. Use the CC lines to decide whether to provide VBUS (and in the worse case may even not provide VBUS power) ?

  2. Once proper validation with the device connected then will be able to provide +5V upto 3A on the VBUS lines ?

Starship - On Strike
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shmueld
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  • Maple "Since Type C is backwards compatible it has to provide at least 500mA for old devices without the use of CC lines. I don't know whether you can use CC to negotiate cutting yourself from any power. It makes little sense so I suspect designers did not even plan for this possibility." This is an interesting point and I would have thought that this should be part of the SPEC ? – shmueld Jun 28 '18 at 09:01
  • Maple: When it comes to PD external power supplies is it correct to assume that if there is not correct CC "communication" between the external supply and the device drawing the power (e.g. if the device's CC capacitance is out of the range of between 200pF - 600pF ) then the external device may not even supply the VBUS ? – shmueld Jun 28 '18 at 09:10
  • I suspect that external power supplies don't do much except indicating available power with resistors. – Maple Jun 28 '18 at 10:42

3 Answers3

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In Host PC that have USB Type C Ports is it correct to assume that they will be implemented with PD controllers

No, it is not correct to assume that every Type-C port uses PD - power delivery specifications. Power Delivery is independent and optional feature.

  1. Use the CC lines to decide whether to provide VBUS (and in the worse case may even not provide VBUS power) ?

This is the standard function of a Type-C port. No need for PD here.

  1. Once proper validation with the device connected then will be able to provide +5V upto 3A on the VBUS lines ?

Again, this is the standard function of a Type-C port, no Power Delivery is necessary. If the port carries the USB host function and is designed to drive up to 3 A power, it should "advertise" this capability by having 10k pullups on CC lines. If the port can source only 1.5 A, it should have 22k pull-up. If there is enough power only for 500 mA, the port should have 56k pull-up to 5V. A simple voltage comparator of device side is sufficient to determine source port power capability. The PD (or its subset) is required only if 5 A is designed in, or higher voltages are used.

Ale..chenski
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In Host PC that have USB Type C Ports is it correct to assume that they will be implemented with PD controllers

It is up to manufacturer whether they support PD or not. Having said that, I suspect all new devices with Type C will support it.

Use the CC lines to decide whether to provide VBUS (and in the worse case may even not provide VBUS power)?

Since Type C is backwards compatible it has to provide at least 500mA for old devices without the use of CC lines. I don't know whether you can use CC to negotiate cutting yourself from any power. It makes little sense so I suspect designers did not even plan for this possibility.

UPDATE:

The above statement was based upon USB PD 3.0 specification. Following the comments by @AliChen I checked Type-C 1.3 specification. Apparently, Type-C ports implement "USB Type-C-specific implementation of the USB Power Delivery Specification". And later: "USB Power Delivery optimized for the USB Type-C connector".

Specifically, Type-C port does not supply 5V until it detects attached sink device and determines its type. So, yes, in worse case it may not provide VBUS (or VCONN) power.

Note that this behavior is allowed by PD spec, which states that downstream port can source either 5V or 0V in its initial state. I suspect that 0V option was added to PD 3.0 in a hurry to accommodate Type-C spec. First, because "source 0V" sounds idiotic, and second, because in some parts of the spec it still mentions only 5V and requires DFP to tolerate 5V supplied from the other side.

Once proper validation with the device connected then will be able to provide +5V upto 3A on the VBUS lines?

If you have port with PD 2.0 and up then yes. For PD 1.0 it's 2A. In either case "You're gonna need a bigger cable". But if you need more power you can try negotiate for 20V 5A, although it is my understanding the host may limit output power to whatever their circuitry can provide.

Maple
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  • Type-C can't operate without using CC lines. – Ale..chenski Jun 28 '18 at 02:32
  • @AliChen from what I gather from the spec, type C _should_ support USB 2.0, 3.1 and BC 1.2 _without_ the use of CC lines, using old USB negotiation mechanism. I might be wrong, of course. – Maple Jun 28 '18 at 09:45
  • Battery Charging was always "optional". Type-C should support all USB data protocols, true, but VBUS cannot be activated without sensing status of CC lines, since the initial state of any Type-C port is VBUS = OFF. – Ale..chenski Jun 28 '18 at 15:17
  • Here is a quote from USB PD 3.0 specification: "Initial operating conditions remain the USB Default Operation as defined in [USB 2.0], [USB 3.2], [USB Type-C 1.3] or [USBBC 1.2]. The DFP sources vSafe5V over VBUS. The UFP consumes power from VBUS". The [wikipedia](https://en.wikipedia.org/wiki/USB-C#USB_2.0/1.1) seems to think so as well. – Maple Jun 28 '18 at 19:03
  • Maybe initial state OFF only applies to dual-function devices? – Maple Jun 28 '18 at 19:21
  • No. PD has almost nothing to do with Type-C. USB, Type-C, and PD are nearly independent and loosely-related specifications. Since Type-C is symmetrical, VBUS must be initially off to prevent power conflicts in accidental host-host connections. – Ale..chenski Jun 28 '18 at 21:09
  • From 3.0 spec: "Sources must have the ability to tolerate vSafe5V applied by both Port Partners". "When PD Capable devices are Attached to each other, the DFPs and UFPs initially default to standard USB Default Operation. The DFP supplies vSafe5V and the UFP draws current in accordance with the rules defined by [USB 2.0], [USB 3.2], [USB Type-C 1.3] or [USBBC 1.2] specifications."; "DFP Source applies vSafe0V or vSafe5V on VBUS"; "If the Source applies vSafe0V as their default, it detects Attach events and transitions its output to vSafe5V upon detecting an Attach" – Maple Jun 28 '18 at 21:29
  • I understand the above as it is up to manufacturer to decide whether it has 0V or 5V as its default, but 5V is preferable since it provides backward compatibility. They only have to make sure they can tolerate 5V applied from the other end. Please understand, I am not trying to be a jerk, I am trying to figure out where I am reading the spec wrong. – Maple Jun 28 '18 at 22:15
  • No, For unconnected port the VBUS=OFF is mandatory. Look Section 4.4.2, *"The Source’s USB Type-C receptacle VBUS pin shall remain unpowered and shall limit the capacitance between VBUS and GND as specified in Table 4-2 until a Sink is attached. The VBUS pin shall return to the unpowered state when the Sink is detached."*. Again, don't confuse yourself with USB 3.x or PD specs, read the Type-C specifications first. – Ale..chenski Jun 29 '18 at 02:36
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A type C port can signal 5V power availability with the CC lines. The options are 3A, 1.5A, or legacy power. (Legacy power is 900mA for USB3, or 500mA for USB2...but you need to stick with 500 unless you're going to negotiate over the USB data lines.)

The primary reason for the CC line encoding is so that your phone can get a charge without negotiating over the data lines. Higher voltages and currents can be negotiated by a device with data capability, including the reverse--charging the laptop through its own USB port.

Although most type C ports are 3A, some aren't...some HP Zbooks, for example, erroneously advertise 1.5A but only supply 900mA.

Cristobol Polychronopolis
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