Dallas DS21T09S Plug and play scsi terminator Datasheet

DS21T09
Plug and Play SCSI Terminator
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
Fully compliant with SCSI-1, Fast SCSI and
Ultra SCSI
Compatible with Plug and Play SCSI Profile
Functional drop in replacement for the
DS2109
Complementary part to DS21T07 for wide
SCSI
Provides active termination for 18 signal lines
2% tolerance on termination resistors and
voltage regulator
Bus termination sensing
Low power-down capacitance of 3 pF
Onboard thermal shutdown circuitry
PDI
R1
R2
R3
R4
R5
HS-GND
HS-GND
PDO
R6
R7
R8
R9
TPWR
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
R18
R17
R16
R15
R14
TCS
HS-GND
PDE
R13
R12
R11
R10
VREF
DS21T09S 28-Pin SOIC (300-mil)
DESCRIPTION
The DS21T09 is intended for one-chip Plug and Play (PnP) SCSI termination. Plug and Play SCSI
requires the exit-point terminator on computer motherboards or host bus adapters to automatically switch
off if an external device is connected to the system. The DS21T09 satisfies this requirement by offering
the engineer a choice of onboard current sensing circuitry or onboard ground detect circuitry. If an
external device is connected, the DS21T09 will automatically be isolated from the SCSI bus thereby
maintaining proper system termination.
The DS21T09 integrates a low drop-out regulator, 18 precisely switched 110Ω=termination resistors, and
bus termination sensors into a 28-pin, 300-mil SOIC package. Active termination provides: greater
immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise
immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T09
contains an output port that can control the power-down pin of additional terminators (DS21T07) for
Wide SCSI applications.
REFERENCE DOCUMENTS
SCSI-2 (X3.131-1994)
SCSI-3 Parallel Interface (X3T10/855D)
Available from: Global Engineering Documents
15 Inverness Way East
Englewood, CO 80112-5704
Phone: (800) 854-7179, (303) 792-2181
Fax: (303) 792-2192
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112099
DS21T09
PnP SCSI Specification
PnP ISA Specification
PnP BIOS Specification
PnP Option ROM Specification
Available from: Plug and Play forum on
CompuServe (Go plugplay).
FUNCTIONAL DESCRIPTION
The DS21T09 is designed to be a single chip termination subsystem for use in PnP SCSI systems, Figure
1. When embedded on a host bus adapter or motherboard, the DS21T09 can automatically sense the
termination status of the SCSI bus and attach or isolate its resistors as needed to maintain proper bus
termination. External and internal active termination can be provided by the DS21T07.
DS21T09 APPLICATION ENVIRONMENT Figure 1
2 of 10
DS21T09
The DS21T09 consists of three major functional blocks, Figure 2:
•
Voltage reference, terminating resistors, and isolation switches
•
Bus current sensing circuitry
•
Bus ground sensing circuitry
When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determines that the SCSI bus
is properly terminated without the DS21T09, the power-down buffer isolates the resistors from the SCSI
bus and disables the power amp, thereby placing the DS21T09 in a low power mode (the bus sensing
circuitry always stays active). The PDO (Power-Down Output) pin can be connected to the pin of a
DS21T07 SCSI terminator for Wide SCSI configurations, Figure 8.
DS21T09 BLOCK DIAGRAM Figure 2
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DS21T09
DETAILED PIN DESCRIPTION Table 1
PIN
1
2-6,
10-13,
16-19,
24-27
7, 8, 21
SYMBOL FCN
DESCRIPTION
I
Power-Down
Internal.
For
Bus Ground Sensing Circuit, connect to pin
PDI
22 of internal SCSI connector; see Figure 4.
R1…R13
T
Signal Termination. 110Ω termination. Connect to SCSI bus signal
R15…R18
lines. For Bus Current Sensing Circuit connect to data, parity, and
control lines, except SCSI-RST line; see Figure 6.
HS-GND
P
9
PDO
O
14
TPWR
P
15
VREF
O
20
PDE
I
22
TCS
I
23
R14
T
28
GND
P
Heat Sink Ground. Internally connected to the mounting pad. Should
be either grounded or electronically isolated from other circuitry.
Power-Down Output. Connect to DS21T07 for Wide SCSI
applications; see Figure 8.
Termination Power. Connect to the SCSI TERMPWR line. Bypass
with a 2.2 µF capacitor; see Figures 4 and 6.
Reference Voltage. 2.85-volt reference; must be decoupled with a 4.7
µF capacitor; see Figures 4 and 6.
Power-Down External. For Bus Ground Sensing Circuit, connect to pin
36 of external SCSI connector; see Figure 4.
Termination Current Sense. Used to sense current on the SCSI bus.
For Bus Current Sensing Circuit, connect to SCSI signal line –RST; see
Figure 6.
Signal Termination. 110Ω termination. Connect to SCSI bus signal
lines. For Bus Current Sensing Circuit connect to SCSI controller chip;
see Figure 6.
Ground. Signal ground; 0.0 volts.
ACTIVE TERMINATION
The voltage regulator circuitry (bandgap reference and class AB power amplifier) produces a precise,
laser-trimmed 2.85-volt level and is capable of sourcing 25 mA into each of the terminating resistors
when the signal line is low (active). When the external driver for a given signal line turns off, the active
terminator will pull that signal line to 2.85 volts (quiescent state). When used with an active negation
driver, the power amp can sink 22 mA per line while keeping the voltage reference in regulation; the
terminating resistors maintain their 110Ω=value over the entire voltage range and Vref will move less than
60 mv. To maintain the specified regulation, a 4.7 µF capacitor is required between the VREF pin and
ground. A high frequency capacitor (0.1 µF ceramic recommended) can also be placed on the Vref pin in
applications that use fast rise/fall time drivers. The power down capacitance on terminating resistors R1R13 and R15-R18 is <3 pF; R14 is slightly higher due to the bus current sensing circuitry.
The DS21T09 can be removed from the SCSI bus by using either of two automatic methods: Bus Ground
Sensing or Bus Current Sensing.
As with all analog circuitry, the TERMPWR lines should be bypassed locally. A 2.2 µF capacitor is
recommended between TPWR and ground. It should be placed as close as possible to the DS21T09. The
DS21T09 should be placed as close as possible to the connector to minimize signal and power trace
length, thereby resulting in less input capacitance and reflections which can degrade the bus signals.
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DS21T09
BUS GROUND SENSING
If internal and external SCSI devices are connected to the SCSI bus, the DS21T09 will disconnect from
the SCSI bus according to the circuit in Figure 3. To utilize this automatic disconnect method of bus
sensing, configure the DS21T09 as shown in Figure 4. The PDI (Power Down Internal) pin should be
connected to pin 22 of the internal SCSI connector, and the PDE (Power Down External) connected to
pin 36 of the external SCSI connector.
BUS GROUND SENSING CIRCUIT Figure 3
BUS GROUND DETECT CONFIGURATION Figure 4
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DS21T09
BUS CURRENT SENSING
The DS21T09 has the capability to use current sensing to determine if the SCSI bus is over- or underterminated. A 1Ω=resistor in series with the SCSI bus (preferable the RST line) is used to monitor the bus
current when that line pulls low (Active or “asserted” state). The resistor is between pad R14 and TCS on
the die. Based on the current measured, the DS21T09 will disconnect or connect from the SCSI bus. The
configuration for this automatic isolation technique is shown in Figure 6.
Figure 5 shows a simplified diagram of the sensing circuit. The voltage across the 1Ω=sense resistor is
differentially amplified and converted into a single-ended voltage with respect to ground. This is fed into
a bank of comparators and measured against a reference voltage. The circuit takes a measurement each
time TCS is driven below a 0.8 volts threshold and the outputs are latched on the rising edge of TCS. If
IBUS is greater than 32 mA, the DS21T09 will be isolated from the SCSI bus. It is recommended that the
signal on TCS be asserted for at least 25 µsec to allow the signal (and comparator outputs) to settle into a
known state. A timing diagram of the sensing and latching operation is shown in Figure 7.
It is preferred that the -RST line be used for monitoring the bus termination status because -RST is only
asserted during power up or during a major change in bus configuration. Note that R14 will have a higher
input capacitance than the other lines because of the additional circuitry required for bus sensing.
The DS21T09 will be isolated from the SCSI bus as shown in Table 2.
BUS CURRENT SENSING CIRCUITRY Figure 5
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DS21T09
BUS CURRENT SENSE CONFIGURATION Figure 6
BUS CURRENT SENSE TIMING DIAGRAM Figure 7
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DS21T09
DISCONNECT MODES Table 2
PDI
PDE
IBUS > 32 mA?
DS21T09 ISOLATED
FROM SCSI BUS?
Isolated
Connected
Connected
Connected
Isolated
Isolated
Isolated
Isolated
0
0
No
0
1
No
1
0
No
1
1
No
0
0
Yes
0
1
Yes
1
0
Yes
1
1
Yes
NOTE: “1” denotes pin left open circuited.
WIDE SCSI CONFIGURATION Figure 8
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DS21T09
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
*
-1.0V to +7.0V
0°C to 70°C
-55°C to +125°C
260°C for 10 seconds
This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
The Dallas Semiconductor DS21T09 is built to the highest quality standards and manufactured for long
term reliability. All Dallas Semiconductor devices are made using the same quality materials and
manufacturing methods. However, the DS21T09 is not exposed to environmental stresses, such as burnin, that some industrial applications require. For specific reliability information on this product, please
contact the factory in Dallas at (972) 371-4448.
RECOMMENDED OPERATING CONDITIONS
PARAMETER
TERMPWR Voltage
Logic 1
Logic 0
SYMBOL
VTP
VIH
VIL
MIN
4.00
2.0
-0.3
(0°C to 70°C)
TYP
MAX
5.25
VTP + 0.3
+0.8
UNITS
V
V
V
MAX
500
14
2
112
UNITS
mA
mA
mA
Ω
°C
pF
pF
µA
µA
mA
mA
DC CHARACTERISTICS
PARAMETER
TERMPWR Current
Power-Down Current
Termination Resistance
Die Thermal Shutdown
Power-Down
Termination Capacitance
Input Leakage High
Input Leakage Low
Output Current
Bus Current Sense
Trip Point
SYMBOL
ITP
ITP
IPD
RTERM
TSD
CPD
C14
IIH
IIL
IO
IBCST
SYMBOL
VREF
VDROP
LIREG
LOREG
IL
ISINK
1
1
(0°C to 70°C)
MIN
TYP
108
10
1
110
150
8
-1.0
1.0
4
32
REGULATOR CHARACTERISTICS
PARAMETER
Output Voltage
Drop Out Voltage
Line Regulation
Load Regulation
Current Limit
Sink Current
NOTES
NOTES
2, 4
2, 5
2, 3, 6
2, 3
2
2, 3, 6, 7
2, 3, 6, 7, 8
2, 12
2, 9, 12
10
11
(0°C to 70°C)
MIN
2.79
9 of 10
TYP
2.85
0.75
1.0
1.3
900
400
MAX
2.93
1.0
2.0
3.0
UNITS
V
V
%
%
mA
mA
NOTES
2, 3
4, 7
2, 5
2, 3
2
2
DS21T09
NOTES:
1. PDI , PDE , TCS
2. 4.00V < TERMPWR < 5.50V.
8. C14 slightly higher capacitance due to
sensing circuitry.
3. 0.0V < signal lines < TERMPWR.
9. Excluding PDI , PDE pins.
4. All signal lines = 0.0V.
10. PDO output pin.
5. All signal lines open.
11. IBCST > 32 mA – disable termination.
6. Power down enabled.
12. Excluding PDE , PDI , R14, and TCS pins.
7. Guaranteed by design; not production tested.
28–PIN SOIC (300-MIL)
The chamfer on the body is optional. If it is not
present, a terminal 1 identifier must be
positioned so that ½ or more of its area is
contained in the hatched zone.
10 of 10
PKG
DIM
A IN.
MM
A1 IN.
MM
A2 IN.
MM
b IN.
MM
C IN.
MM
D IN.
MM
e IN.
MM
E1 IN.
MM
H IN.
MM
L IN.
MM
Θ
28-PIN
MIN
MAX
0.094
0.105
2.39
2.67
0.004
0.012
0.102
0.30
0.089
0.095
2.26
2.41
0.013
0.020
0.33
0.51
0.009
0.013
0.229
0.33
0.698
0.712
17.73
18.08
0.050 BSC
1.27 BSC
0.290
0.300
7.37
7.62
0.398
0.416
10.11
10.57
0.016
0.040
0.40
1.02
0°
8°
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