HP7501 Datasheet, PDF (2/9 Pages) List of Unclassifed Manufacturers – Ultra320 LVD/SE SCSI Terminator

HP7501
Ultra320 LVD/SE SCSI Terminator
ORDERING INFOMATION
PART NUMBER
HP7501-A36
HP7501-T28
PIN - PACKAGE
SSOP-36 pin
TSSOP-28 pin
FUNCTIONAL DESCRIPTION
HP 7501 is a multi-mode active terminator with
automatically switching on LVD/SE/HVD mode. The
DIFFSENS* is on one of three voltage levels to indicate
LVD/SE/HVD mode. If the voltage on DIFFSESE** is
above 2.16V, below 0.6V or between, that indicates the
bus mode to be HVD, SE, or LVD.
In Figure 1, a bandgap reference is fed into an buffer
to generate reference voltages. A voltage selected by the
control logic through a MUX is used to generate 2.85V or
1.25V reference voltages. A voltage 2.85V and 1.25V is
used in SE mode and LVD mode respectively. The
voltage for a specific mode is sent out through an op
buffer. In SE mode, the RxP pin is switched to ground.
DIFF_CAP with a RC low pass filter monitors the
voltage on DIFFSENS to determine the termination mode
used on bus. The DIFFERENSE CIRCUITRY decodes
the trinary voltage on DIFF_CAP and generates three
control logic signals internally. The control logic will
change the total termination resistance and switch to one
of three termination modes based on the voltage on
DIFFSENS.
SE Mode: The voltage on DIFFSENSE is between
0V - 0.5V. RxP pin is grounded. When the external driver
for a given line turns off, the active terminator will pull
that signal line to 2.85V (quiescent state). When
operated in an active negation driver, the power amp can
sink 22mA per line and the reference voltage won’t
change over 100mV. The termination resistors maintain
110ohm.
HVD Mode: The voltage on DIFFSENSE is above
2.4V. HP7501 will identify that there is an HVD (high
voltage differential) device on the SCSI bus and isolate
the termination pins from the bus.
LVD Mode: The voltage on DIFFSENSE is between
0.7–1.9V. A precious resistor string between two current
sources provides LVD termination. It offers a 105 ohm
differential mode impedance and a 125 ohm common
mode impedance. A fail-safe bias of 112mV is maintained
when no driver is connected to the SCSI bus.
During high temperature (>150 ℃ ), HP7501 would
thermal shutdown. The termination pins are isolated from
SCSI bus and Vref becomes high impedance. When
ISO=1, the termination pins are isolated from the SCSI
bus, but the bus mode indicators (SE/LVD/HVD) and Vref
remain active. In the above two cases, the DIFFSENSE
driver is shut down and in high impedance.
The TPWR pin is connected to the SCSI bus
TERMPWR line to power up the HP7501. The TERMPWR
line should be bypassed locally. A 2.2uF capacitor and a
0.01uF high frequency capacitor between TPWR and
ground are suggested for different frequency noise.
Capacitors should be placed as close as possible to the
HP7501. The HP7501 should be placed as close as
possible to the SCSI connector to minimize input signal
trace length and result in less reflections and better
performance.
To maintain the specified voltage, a 4.7uF capacitor is
recommended between the Vref (pin36) and ground. A
high frequency capacitor (0.1uF ceramic recommended)
can also be placed on the Vref pin in applications the use
fast rise/fall time drivers. It is also recommended to place
a RC low pass filter between DIFFSENSE and DIF_CAP
to lower noise from the SCSI bus.
DIFFSENS Noise Filtering: The HP7501
incorporates a digital filter to remove high frequency
transients on the DIFFSENS control line. The external
filter may be used as well in addition to the internal digital
filter.
A typical SCSI bus configuration is shown in Figure 2.
NOTE:
* DIFFSENS: Refers to the SCSI bus signal
** DIFFSENSE: Refers to the pin name in HP7501.
2003/05/12 Ver. 0.0
2
HIMARK TECHNOLOGY INC.