ISP1160
Embedded USB Host Controller
Philips Semiconductors
9.8.1 Using an internal OC detection circuit
The internal OC detection circuit can be used only when VCC (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 26. 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_N detects an overcurrent status on a downstream port, H_PSWn_N
will output HIGH, a logic 1 to turn off the 5 V power supply to the downstream port
VBUS. When there is no such detection, H_PSWn_N will output LOW, a logic 0 to turn
on the 5 V power supply to the downstream port VBUS
.
In general applications, a P-channel MOSFET can be used as the power switch for
VBUS. Connect the 5 V power supply to the drain of the P-channel MOSFET, VBUS to
the source, and H_PSWn_N to the gate. Call the voltage drop across the drain and
source, the overcurrent detection voltage (VOC). For the internal overcurrent detection
circuit, a voltage comparator has been designed-in, with a nominal voltage threshold
(∆Vtrip) of 75 mV. When VOC exceeds Vtrip, H_PSWn_N will output a HIGH level,
logic 1 to turn off the P-channel MOSFET. If the P-channel MOSFET has a RDSon of
150 mΩ, the overcurrent threshold will be 500 mA. The selection of a P-channel
MOSFET with a different RDSon will result in a different overcurrent threshold.
regulator
P-Channel
HC CORE
HcHardware
MOSFET
V
CC
+
5 V
OC detect
Configuration
OC select
bit 10
1
≥
+
V
=
5 V − V
BUS
OC
H_OCn_N
0
Reg
V
BUS
PSW
H_PSWn_N
C/L
USB
downstream
port
connector
22 Ω
H_DMn
ATX
SIE
22 Ω
H_DPn
bit 12
47 pF
(2×)
HcHardware
Configuration
15 kΩ
(2×)
ISP1160
004aaa066
’n’ represents the downstream port number (n = 1 or 2).
Fig 26. Using an internal OC detection circuit.
9397 750 11371
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
Product data
Rev. 04 — 04 July 2003
33 of 88
NXP [ NXP ]
