DS21S07AE+ [MAXIM]
SCSI Terminator, 9-Line, 110ohm, PDSO20, 4.40 MM, PLASTIC, TSSOP-20;
| 型号： | DS21S07AE+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | SCSI Terminator, 9-Line, 110ohm, PDSO20, 4.40 MM, PLASTIC, TSSOP-20 |
| 文件： | 总10页 (文件大小：89K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
DS2109
DS2109
Plug and Play SCSI Terminator
FEATURES
PIN ASSIGNMENT
• Fully compliant with SCSI–1, Fast SCSI and Ultra
PDI
R1
1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
R18
SCSI
2
• Compatible with Plug and Play SCSI Profile
• Functionally compatible with DS21S07A
• Provides active termination for 18 signal lines
R2
3
R17
R3
4
R16
R4
5
R15
R5
6
R14
HS–GND
HS–GND
PDO
R6
7
TCS
HS–GND
PDE
R13
• 2% tolerance on termination resistors and voltage
regulator
8
9
• Bus termination sensing
10
11
12
13
14
R7
R12
• Low power down capacitance of 3 pF
• Onboard thermal shutdown circuitry
R8
R11
R9
R10
TPWR
V
REF
DS2109, DS2109S 28–PIN SOIC (300 MIL)
DESCRIPTION
The DS2109 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 exter-
naldeviceisconnectedtothesystem. TheDS2109sat-
isfies 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
DS2109 will automatically be isolated from the SCSI
bus thereby maintaining proper system termination.
The DS2109 integrates a low drop–out regulator, 18
precise switched 110 ohm termination resistors, and
bus termination sensors into a 28–pin 300 mil SOIC
package. Active termination provides: greater immu-
nity to voltage drops on the TERMPWR (TERMination
PoWeR) line, enhanced high–level noise immunity,
intrinsic TERMPWR decoupling, and very low quies-
cent current consumption. The DS2109 contains an
output port that can control the power down pin of addi-
tional terminators (DS21S07A) for Wide SCSI applica-
tions.
022698 1/10
DS2109
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
FUNCTIONAL DESCRIPTION
The DS2109 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 mother-
board, the DS2109 can automatically sense the ter-
mination status of the SCSI bus and attach or isolate its
resistors as needed to maintain proper bus termination.
Externalandinternalactiveterminationcanbeprovided
by the DS21S07A.
PnP SCSI Specification
PnP ISA Specification
PnP BIOS Specification
PnP Option ROM Specification
Available from: Plug and Play forum on
CompuServe (Go plugplay).
DS2109 APPLICATION ENVIRONMENT Figure 1
PERIPHERAL
SUBSYSTEM
EXTERNAL
TERMINATOR
(TWO DS21S07A)
DS2109 AUTOMATIC
EXIT–POINT TERMINATOR
50–POSITION
HIGH DENSITY
CONNECTORS
SCSI EXTERNAL
CABLE
HOST SCSI
PROTOCOL CHIP
SCSI INTERNAL
CABLES
SCSI
PERIPHERAL
DEVICES
INTERNAL
TERMINATOR
(TWO DS21S07A)
022698 2/10
DS2109
The DS2109 consists of 3 major functional blocks,
Figure 2:
erly terminated without the DS2109, the power down
buffer isolates the resistors from the SCSI bus and dis-
ables the power amp, thereby placing the DS2109 in a
low power mode (the bus sensing circuitry always stays
active). The PDO (Power Down Output) pin can be con-
nected to the pin of a DS21S07A SCSI terminator for
Wide SCSI configurations, Figure 8.
• Voltagereference, terminatingresistors, andisolation
switches
• Bus current sensing circuitry
• Bus ground sensing circuity
When the Bus Ground Sensing Circuitry or Bus Current
Sensing Circuitry determine that the SCSI bus is prop-
DS2109 BLOCK DIAGRAM Figure 2
PDI
BUS GROUND
SENSING
CIRCUITRY
BUS CURRENT
SENSING
TCS
DISABLE
DISABLE
CIRCUITRY
PDE
PDO
POWER
DOWN
BUFFER
110 OHMS
110 OHMS
BANDGAP
REFERENCE
R14
R18
+
–
110 OHMS
R1
V
REF
022698 3/10
DS2109
DETAILED PIN DESCRIPTION Table 1
PIN
SYMBOL
FCN
DESCRIPTION
1
PDI
I
Power Down Internal. For Bus Ground Sensing Circuit connect to pin 22
of internal SCSI connector, see Figure 4.
2–6,
R1...R13
R15...18
T
Signal Termination. 110 ohm termination. Connect to SCSI bus signal
lines. For Bus Current Sensing Circuit connect to data, parity, and control
lines, except SCSI–RST line, see Figure 6.
10–13,
16–19,
24–27
7, 8, 21
HS–GND
PDO
P
O
P
O
I
Heat Sink Ground. Internally connected to the mounting pad. Should be
either grounded or electronically isolated from other circuitry.
9
Power Down Output. Connect to DS21S07A for Wide SCSI applica-
tions, see Figure 8.
14
TPWR
Termination Power. Connect to the SCSI TERMPWR line. Bypass with
a 2.2 µF capacitor, see Figures 4 and 6.
15
V
REF
Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7 µF
capacitor, see Figures 4 and 6.
20
PDE
TCS
Power Down External. For Bus Ground Sensing Circuit, connect to pin
36 of external SCSI connector, see Figure 4.
22
I
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.
23
28
R14
T
P
Signal Termination. 110 ohm termination. Connect to SCSI bus signal
line. For Bus Current Sensing Circuit connect to SCSI controller chip, see
Figure 6.
GND
Ground. Signal ground; 0.0 volts.
As with all analog circuitry, the TERMPWR lines should
ACTIVE TERMINATION
The voltage regulator circuitry (bandgap reference and
class AB power amplifier) produces a precise laser–
trimmed2.85voltlevelandiscapableofsourcing24mA
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
valueovertheentirevoltagerange. Tomaintainthespe-
cified regulation, a 4.7 µF capacitor is required between
be bypassed locally. A 2.2 µF capacitor is recom-
mended between TPWR and ground and placed as
close as possible to the DS2109. The DS2109 should
be placed as close as possible to the connector to mini-
mize signal and power trace length, thereby resulting in
less input capacitance and reflections which can
degrade the bus signals.
BUS GROUND SENSING
If internal and external SCSI devices are connected to
theSCSIbus,theDS2109willdisconnectfromtheSCSI
bus according to the circuit in Figure 3. To utilize this
automatic disconnect method of bus sensing, configure
the DS2109 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 con-
nector.
the V
pin and ground. A high frequency cap (0.1 µF
REF
ceramicrecommended) can also be placed on the V
REF
pin in applications that use fast rise/fall time drivers. The
power down capacitance on terminating resistors
R1–R13 and R15–R18 is <4 pF; R14 is slightly higher
due to the bus current sensing circuitry.
The DS2109 can be removed from the SCSI bus by
using either of two automatic methods, Bus Ground
Sensing or Bus Current Sensing.
022698 4/10
DS2109
BUS GROUND SENSING CIRCUIT Figure 3
PDI
DISABLE
PDE
BUS GROUND DETECT CONFIGURATION Figure 4
INTERNAL SCSI CONNECTOR
22
26
TERMPWR
38
2.2 µF
DS2109
PDI
GND
36
PDE
TPWR
V
REF
4.7 µF
022698 5/10
DS2109
driven below a 0.8 volts threshold and the outputs are
latched on the rising edge of TCS. If I is greater than
BUS CURRENT SENSING
TheDS2109 has the capability to use current sensing to
determine if the SCSI bus is over– or under–terminated.
A series 1 ohm resistor between pads R14 and TCS is
inserted into the SCSI bus (preferably the –RST line)
and used to monitor the current when that line pulls low
(active, or “asserted” state). Based on the current mea-
sured, the DS2109 will disconnect or connect from the
SCSI bus. The configuration for this automatic isolation
technique is shown in Figure 6.
BUS
32mA, theDS2109willbeisolatedfromtheSCSIbus. It
is recommended that the signal on TCS be asserted for
atleast25msectoallowthesignal(andcomparatorout-
puts)tosettleintoaknownstate. Atimingdiagramofthe
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
busconfiguration. NotethatR14willhaveahigherinput
capacitance than the other lines because of the addi-
tional circuitry required for bus sensing.
Figure 5 shows a simplified diagram of the sensing cir-
cuit. The voltage across the 1 ohm sense resistor is dif-
ferentially 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 volt-
age. The circuit takes a measurement each time TCS is
The DS2109 will be isolated from the SCSI bus as
shown in Table 2.
BUS CURRENT SENSING CIRCUITRY Figure 5
TO SCSI CONTROLLER
FROM SCSI BUS (–RST)
R14
TCS
1 OHM
I
BUS
110 OHM
– +
REF
DECODE
AND
LATCH
022698 6/10
DS2109
BUS CURRENT SENSE CONFIGURATION Figure 6
INTERNAL SCSI
CONNECTOR
26
40
TERMPWR
38
DS2109
R1
TPWR
2.2 µF
R13
R15
V
REF
R18
45
TCS
R14
4.7 µF
–RST
GND
–RST
SCSI
CONTROLLER
BUS CURRENT SENSE TIMING DIAGRAM Figure 7
25 µs min
TCS
COMPARATORS
LATCH
022698 7/10
DS2109
DISCONNECT MODES Table 2
DS2109 ISOLATED
FROM SCSI BUS?
PDI
0
PDE
I
> 32 mA?
No
BUS
0
1
0
1
0
1
0
1
Isolated
Connected
Connected
Connected
Isolated
0
No
1
No
1
No
0
Yes
Yes
Yes
Yes
0
Isolated
1
Isolated
1
Isolated
NOTE: “1” denotes pin left open circuited.
WIDE SCSI CONFIGURATION Figure 8
TERMINATION POWER LINE
2.2 µF
TERMPWR1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PD
PDI
R1
1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
R18
R1
R2
R3
R4
R5
V
2
REF2
NC
R2
3
R17
R3
4
R16
R9
R4
5
R15
R8
R5
6
R14
R7
HS–GND
HS–GND
PDO
R6
7
TCS
HS–GND
PDE
R13
V
R6
REF1
8
GND
TERMPWR2
9
DS21S07A 16–PIN SOIC (300 MIL)
10
11
12
13
14
R7
R12
R8
R11
R9
R10
4.7 µF
TPWR
V
REF
4.7 µF
DS2109S 28–PIN SOIC (300 MIL)
022698 8/10
DS2109
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
–1.0V to +7.0V
0°C to 70°C
Storage Temperature
Soldering Temperature
–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.
RECOMMENDED OPERATING CONDITIONS
(0°C to 70°C)
PARAMETER
TERMPWR Voltage
Logic 1
SYMBOL
MIN
4.00
2.0
TYP
MAX
UNITS
NOTES
V
TP
5.25
V
V
V
V
IH
V
+0.3
1
1
TP
Logic 0
V
IL
–0.3
+0.8
DC CHARACTERISTICS
PARAMETER
(0°C to 70°C)
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
TERMPWR Current
I
I
500
14
mA
mA
2, 4
2, 5
TP
TP
10
1
Power Down Current
Termination Resistance
Die Thermal Shutdown
I
2
mA
ohms
°C
2, 3, 6
2, 3
2
PD
R
108
110
150
112
TERM
TS
D
Power Down Termination
Capacitance
C
C
3
8
4.5
1.0
pF
pF
2, 3, 6, 7
2,3,6,7,8
PD
14
Input Leakage High
Input Leakage Low
Output Current
I
IH
–1.0
4
µA
µA
2, 12
2, 9, 12
10
I
IL
I
mA
mA
O
Bus Current Sense Trip Point
I
32
11
BCST
REGULATOR CHARACTERISTICS
(0°C to 70°C)
PARAMETER
Output Voltage
Drop Out Voltage
Line Regulation
Load Regulation
Current Limit
SYMBOL
MIN
TYP
2.85
0.75
1.0
MAX
2.91
1.0
UNITS
V
NOTES
V
REF
2.79
2, 3
4, 7
2, 5
2, 3
2
V
DROP
V
LI
REG
2.0
%
LO
1.3
3.0
%
REG
I
L
700
400
mA
mA
Sink Current
I
2
SINK
022698 9/10
DS2109
NOTES:
1. PDI, PDE, TCS
2. 4.00V < TERMPWR < 5.25V.
3. 0.0V < signal lines < 3.0V.
4. All signal lines = 0.0V.
5. All signal lines open.
6. Power down enabled.
7. Guaranteed by design; not production tested.
8. C slightly higher capacitance due to sensing circuitry.
14
9. Excluding PDI, PDE pins.
10.PDO output pin.
11. I
> 32 mA – disable termination.
BCST
12.Excluding PDE, PDI, R14, and TCS pins.
28–PIN SOIC (300 MIL)
PKG
DIM
28–PIN
MIN
MAX
A IN.
MM
0.094
2.39
0.105
2.67
A1 IN.
MM
0.004
0.102
0.012
0.30
A2 IN.
MM
0.089
2.26
0.095
2.41
b IN.
MM
0.013
0.33
0.020
0.51
C IN
MM
0.009
0.229
0.013
0.33
D IN.
MM
0.698
17.73
0.712
18.08
e IN.
MM
0.050 BSC
1.27 BSC
The chamfer on the body is optional. If it is not present, a termi-
nal 1 identifier must be positioned so that 1/2 or more of its area
is contained in the hatched zone.
E1 IN.
MM
0.290
7.37
0.300
7.62
H IN
MM
0.398
10.11
0.416
10.57
L IN
MM
0.016
0.40
0.040
1.02
Θ
0°
8°
022698 10/10
相关型号：
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SCSI Terminator, 9-Line, 110ohm, PDSO16, 0.300 INCH, LEAD FREE, PLASTIC, SOIC-16
MAXIM
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