S2R72A21 Application Note
Seiko Epson Corporation
11
(Rev.1.00)
3.4
HS transmission current control
HS transmission current control function (ADJ function) is a feature which controls the current used for
transmitting from either INT or EXT port during HS connection. By this feature, it enables to control the
amplitude of the USB signal. Please refer to the S2R72A21 data sheet section 6.4.1 for details.
This section explains cautions when setting ADJ function.
Figure 3.4.1 shows a USB system example including USB cable and schematic diagrams of HS signal amplitude
in the form of Eye pattern.
Figure 3.4.1
A USB system example and schematic diagrams of HS signal amplitude
HS packets transmitted from the Host are re-synchronized by S2R72A21, and reach the Device through the USB
Cable. P1 is the signal measuring point at the S2R72A21 pin, and P2 is the signal measuring point at the Device.
The HS signal transmitted from the S2R72A21 is attenuated by the USB cable, etc., thus the signal amplitude at
P1 is greater than that at P2 as shown in the figure.
The S2R72A21 detects the disconnection when the SOF amplitude level exceeds the threshold at its pin.
Therefore, please configure the ADJ settings with care not to exceed the disconnect detection threshold at P1.
Host
DP
DM
Device
S2R72A21
INT_DP
INT_DM
EXT_DP
EXT_DM
USB Cable
DP
DM
NG
OK
P1
P2
HS
Packet
HS
Packet
