Microchip Technology USB5744, Руководство пользователя

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USB5744
DS00001855E-page 26

2015-2017 Microchip Technology Inc.
8.4 Port Control Interface
Port power and over-current sense share the same pin (
PRT_CTLx
) for each port. These functions can be controlled
directly from the USB hub, or via the processor.
The device can be configured into the following port control modes:
• Ganged Mode
• Combined Mode
Port connection in various modes are detailed in the following subsections.
8.4.1 PORT CONNECTION IN GANGED MODE
In this mode, one pin (
GANG_PWR
) is used to control port power and over-current sensing.
8.4.2 PORT CONNECTION IN COMBINED MODE
8.4.2.1 Port Power Control using USB Power Switch
When operating in combined mode, the device will have one port power control and over-current sense pin for each
downstream port. When disabling port power, the driver will actively drive a '0'. To avoid unnecessary power dissipation,
the pull-up resistor will be disabled at that time. When port power is enabled, it will disable the output driver and enable
the pull-up resistor, making it an open drain output. If there is an over-current situation, the USB Power Switch will assert
the open drain OCS signal. The Schmidt trigger input will recognize that as a low. The open drain output does not inter-
fere. The over-current sense filter handles the transient conditions such as low voltage while the device is powering up.
When the port is enabled, the
PRT_CTLx
pin input is constantly sampled. Overcurrent events can be detected in one
of two ways:
• Single, continuous low pulse (consecutive low samples over t
ocs_single
), as shown in Figure 8-3 .
• Two short low pulses within a rolling window (two groupings of 1 or more low samples over t
ocs_double
), as shown
in Figure 8-4 .
FIGURE 8-2: PORT POWER CONTROL WITH USB POWER SWITCH
FIGURE 8-3: SINGLE LOW PULSE OVERCURRENT DETECTION
USB Power
Switch
50k
PRTPWR
EN
OCS
OCS
Pull-Up Enable
5V
USB
Device
FILTER
PRT_CTLx
PRT_CTLx
IS V
IL
t
ocs_single