ISP1362
Single-chip USB OTG controller
Philips Semiconductors
12.8.1 Using internal OC detection circuit
An application using the internal OC detection circuit and internal 15 kΩ pull-down
resistors is shown in Figure 23, where DMn denotes either OTG_DM1 or H_DM2,
while DPn denotes either OTG_DP1 or H_DP2. In this example, the HC Driver must
set both AnalogOCEnable and ConnectPullDown_DS1 (bit 10 and bit 12 of the
HcHardwareConfiguration register, respectively) to logic 1.
When H_OCn detects an overcurrent status on a downstream port, H_PSWn will
output HIGH to turn off the +5 V power supply to the downstream port VBUS. When
there is no such detection, H_PSWn will output LOW to turn on the +5 V power
supply to the downstream port VBUS
.
In general applications, you can use a P-channel MOSFET as the power switch for
VBUS. Connect the +5 V power supply to the drain pole of the P-channel MOSFET,
VBUS to the source pole, and H_PSWn to the gate pole. This voltage drop (∆V) across
the drain and source poles can be called the overcurrent trip voltage. For the internal
overcurrent detection circuit, a voltage comparator has been designed-in, with a
nominal voltage threshold of 75 mV. Therefore, when the overcurrent trip voltage (∆V)
exceeds the voltage threshold, H_PSWn will output a HIGH level to turn off the
P-channel MOSFET. If the P-channel MOSFET has 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.
V
DD_5V
PSU_5V
drain
C18
R31
0.1 µF
10 kΩ
P_channel
MOSFET
gate
source
H_PSWn
H_OCn
FB2
(1)
C41
C17
0.1 µF
1
2
3
4
5
6
DGND
DGND
V
BUS
DM
DP
GND
chassis
chassis
004aaa148
DGND
(1) 100 µF for the host port or 4.7 µF for the OTG port.
Fig 23. Using internal OC detection circuit.
12.8.2 Using external OC detection circuit
When VCC (pin 56) is connected to the +3.3 V power supply instead of the +5 V
power supply, the internal OC detection circuit cannot be used. An external
OC detection circuit must be used instead. Nevertheless, regardless of VCC
connection, an external OC detection circuit can be used from time to time. To use an
9397 750 12337
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Product data
Rev. 03 — 06 January 2004
47 of 150
NXP [ NXP ]
