MIC2537 Datasheet, PDF (10/12 Pages) Micrel Semiconductor – Quad Power Distribution Switch Preliminary Information

MIC2537
USB Voltage Regulation
USB specifications require a minimum downstream voltage
supply of 4.40V from a bus-powered hub port (See Applica-
tion Note 17 for details). The USB specification allows for a
100mV drop across the hub, leaving 250mV for PCB, up-
stream cable, and connector resistance. Therefore, the on-
resistance of the switch for each port, not including PCB
resistance, must be about 100mV ÷ 100mA = 1Ω. The
MIC2537 has a maximum on-resistance of 700mΩ, which
easily satisfies this requirement.
Micrel
Overcurrent Indication
The USB Specification does not require bus-powered hubs to
report overcurrent conditions to the host since the hub is
already current-limited at the upstream port. However, if it is
desired to report overcurrent, the Hub Descriptor Status
Register must be programmed to indicate this. The MIC2537
provides a flag output for this application.
December 1999
10
MIC2537