ISP1161A1 Datasheet, PDF (40/136 Pages) NXP Semiconductors – Universal Serial Bus single-chip host and device controller

Philips Semiconductors
ISP1161A1
USB single-chip host and device controller
9.8.1 Using an internal OC detection circuit
The internal OC detection circuit can be used only when V_CC (pin 56) is connected to
a 5 V power supply. The HCD must set AnalogOCEnable, bit 10 of the
HcHardwareConfiguration register, to logic 1.
An application using the internal OC detection circuit and internal 15 kΩ pull-down
resistors is shown in Figure 35. In this example, the HCD must set both
AnalogOCEnable and DownstreamPort15KresistorSel to logic 1. They are bit 10 and
bit 12 of the HcHardwareConfiguration register, respectively.
When H_OCn detects an overcurrent status on a downstream port, H_PSWn will
output HIGH, a logic 1 to turn off the 5 V power supply to the downstream port V_BUS.
When there is no such condition, H_PSWn will output LOW, a logic 0 to turn on the
5 V power supply to the downstream port V_BUS.
In general applications, you can use a P-channel MOSFET as the power switch for
V_BUS. Connect the 5 V power supply to the source of the P-channel MOSFET, V_BUS to
the drain, and H_PSWn to the gate. Call the voltage drop across the drain and source
the overcurrent detection voltage (V_OC). For the internal overcurrent detection circuit,
a voltage comparator has been incorporated with a nominal voltage threshold (∆V_trip)
of 75 mV. When V_OC exceeds V_trip, H_PSWn will output a HIGH level, logic 1 to turn
off the P-channel MOSFET. If the P-channel MOSFET has a R_DSon of 150 mΩ, the
overcurrent threshold will be 500 mA. The selection of a P-channel MOSFET with a
different R_DSon will result in a different overcurrent threshold.
+5 V
VOC = +5 V − VBUS
VBUS
USB
downstream
port
connector
P-Ch
MOSFET
VCC
H_OCn
H_PSWn
22 Ω
22 Ω
47 pF
(2×)
H_DMn
H_DPn
regulator
OC detect
≥
HC CORE
OC select
1
HcHardware
Configuration
bit 10
0 _Reg
PSW
C/ L
ATX
SIE
bit 12 _HcHardware
Configuration
15 kΩ
(2×)
ISP1161A1
‘n’ represents the downstream port number (n = 1 or 2)
Fig 35. Using internal OC detection circuit.
9397 750 13961
Product data
Rev. 03 — 23 December 2004
004aaa182
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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