SYSREG — System regulator

The VBUS input current limiter manages VBUS current limitation and charger detection for USB Type-C compatible chargers.

It supplies VSYS but does not regulate its voltage. VBUS voltage is seen at VSYS as a supply, if the VBUS voltage is within specified limits.

There are two USB compliant, accurate current limits: IBUS_100MA (100 mA) and IBUS_500MA (500 mA).

In addition, there are current limits in 100 mA steps from 600 mA to 1500 mA. The 1500 mA limit is compatible with USB Type-C.

The default current limit is IBUS_100MA (100 mA). Host software can configure the current in register VBUSINILIM0.

The overvoltage threshold for VBUS is VBUS_OVP. The undervoltage threshold for VBUS is VBUS_MIN.

SYSREG is disabled when VBUS_voltage is above the overvoltage threshold VBUS_OVP, or below the undervoltage threshold VBUS_MIN. This isolates VBUS and prevents current flowing from VSYS to VBUS.

USB charger detection is performed through pins CC1 and CC2. These pins must be connected directly to the USB connector for detection to happen.

These pins have internal pull-downs with resistance equal to R_d.

When the device is plugged into a wall adaptor or USB power source, USB port detection runs automatically. One of the CC lines is connected to a pull-up at the source. The other CC line stays pulled down. The voltage over the corresponding R_d determines if a connection was made and if SYSREG can deliver 500 mA or higher current.

Comparators with thresholds at V_RDCONN, V_RD1A5, and V_RD3A monitor CC line voltage when VBUS is present. All comparator output is debounced with t_RDDEB and available to host software through register USBCDETECTSTATUS.

If enabled, an interrupt is issued to the host whenever a threshold is crossed (when voltage decreases or increases). The events are visible in register EVENTSVBUSIN1SET.

The USB power source capability is detected by one CC line at a time, depending on the orientation of the USB plug on the device. The other CC line remains at 0 V. The charger type is defined in the VBUSIN.CC1CMP or VBUSIN.CC2CMP field, depending on which pin is used for connection.

The default VBUS current limit of 100 mA is used until the power source capability is detected. Host software can update the VBUS current limit in VBUSINILIM0 after device detection. When a USB cable is unplugged and plugged back in, or a reset occurs, the default current limit is used.

If USB Type-C configuration is not used, CC1 and CC2 can be left floating or connected to ground. The default VBUS current limit will remain at 100 mA until the host negotiates and configures a higher current.

The device can satisfy USB2.0 Selective Suspend mode current consumption through configuration. It must be informed by host software through the TWI in register VBUSSUSPEND to minimize current consumption from VBUS to I_SUSP.

The current consumed through pin VBUSOUT is not included. VBUS is disconnected from VSYS but VBUSOUT remains active. As a consequence, charging is paused. The device exits this mode only when instructed by the host software through a TWI command. Charging resumes automatically.

The device supplies VBUSOUT voltage when VBUS voltage is present.

VBUSOUT provides overvoltage and undervoltage protection for safe connection to the nRF device. Designs using the VBUSOUT pin as a supply must make sure the voltage level complies with the nRF device due to output resistance R_VBUSOUT. When USB is suspended, the combined current for nPM1300 and the VBUSOUT pin must be within the allowed USB suspend current.

VBUSOUT must have a decoupling capacitor.

The following graphs show typical electrical characteristics for VBUSIN.

Figure 1. VSYS voltage vs. VBUS current, ILIM = 100 mA

Figure 2. VSYS voltage vs. VBUS current, ILIM = 500 mA