9.1.2 Use of GD Internal Clamp

As described in the Configuring Power Capabilities (PSEL, PCTRL, HIPWR) section, the GD pin has an internal clamp. Figure 43 shows an example of how it may be used. V_OUT is the voltage from a power supply that is to be provided onto the VBUS wire of the USB Type-C cable through an NFET. If V_OUT drops, the NFET should be automatically disabled by the device. This can be accomplished by tying the GD pin to V_OUT via a resistor.

The internal resistance of the GD pin is specified to exceed R_GD, and the input threshold is V_{GD_TH}. The GD pin would therefore draw no more than V_{GD_TH}(max) / R_GD(min) < 603 nA. As an example, assume the minimum value of V_OUT for which GD should be high is 4.5 V, then the resistor between GD and V_OUT may not exceed (4.5 – V_{GD_TH}(max) / 603e-9 = 4.5 MΩ. To make it robust against board leakage a smaller resistor such as 1 MΩ can be chosen, but the smaller the resistance the more leakage current into the GD pin. In this example, when V_OUT is 25 V, the current into the GD pin is (25-V_GDC) / 1e6 < 18.5 µA.

Figure 43. Use of GD Internal Clamp