DS21T07
SCSI Terminator
www.dalsemi.com
FEATURES
Fully compliant with SCSI–1, Fast SCSI and
Ultra SCSI
Backward compatible to the DS2107,
DS2107A, and DS21S07
Provides active termination for nine signal
lines
Laser–trimmed 110 ohms termination
resistors have 2% tolerance
Low dropout voltage regulator
Power–down mode isolates termination
resistors from the bus
SCSI bus hot–plug compatible
Fully supports actively negated SCSI signals
Onboard thermal shutdown circuitry
16–pin plastic SOIC (DS21T07S) and 20–pin
plastic TSSOP (Thin Shrink Small Outline
Package) (DS21T07E)
PIN ASSIGNMENT
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PD
VREF2
NC
R9
R8
R7
R6
TERMPWR2
DS21T07S 16-pin SOIC (300-mil)
TERMPWR1
HS-GND
R1
R2
R3
R4
R5
HS-GND
VREF1
GND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
PD
VREF2
HS-GND
NC
R9
R8
R7
R6
HS-GND
TERMPWR2
DS21T07E 20-pin TSSOP (173-mil)
ACTUAL FOOTPRINT SIZE
0.41”
0.26”
0.41”
0.27”
DS21T07S
DS21T07E
DESCRIPTION
Fast SCSI and Ultra SCSI require the use of active terminations at both ends of every cable segment in a
SCSI system with single-ended drivers and receivers. The DS21T07 SCSI Terminator, which is fully
compliant with these standards, enables the designer to gain the benefits of active termination: 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 DS21T07
integrates a regulator and nine precise switched 110 ohms termination resistors into a monolithic IC. The
DS21T07 can be electrically isolated from the SCSI bus without physical removal from the SCSI device.
1 of 7
112099
DS21T07
FUNCTIONAL DESCRIPTION
The DS21T07 consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1).
The bandgap reference circuit produces a precise 2.55V level which is fed to a buffer amplifier. The
buffer produces a 2.85V level and is capable of sourcing at least 24 mA into each of the termination
resistors when the signal line is low (active). When the driver for a given signal line turns off, the
terminator will pull the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals,
the buffer can sink at least 200 mA, and V
REF
will move less than 60 mV. When all lines settle in the
quiescent state, the regulator will consume about 5 mA. When the DS21T07 is put into power-down
mode by bringing
PD
low, the power-down circuitry will turn off the transistors on each signal line. This
will isolate the DS21T07 from the signal lines and effectively remove it from the circuit. The power-
down pin (
PD
) has an internal 50KΩ=pullup resistor. To place the DS21T07 into an active state, the
PD
pin should be left open circuited. When installed on disk drives or RAID system components, the
DS21T07 will not affect the SCSI bus during a hot plug operation.
To ensure proper operation, both the TERMPWR1 and TERMPWR2 pins must be connected to the SCSI
bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each
DS21T07 requires a 4.7 µF capacitor connected between the VREF pins and ground. Figure 2 details a
typical SCSI bus configuration. In an 8-bit wide SCSI bus arrangement, two DS21T07’s would be needed
at each end of the SCSI cable in order to terminate the 18 active signal lines. In a 16-bit wide SCSI bus
arrangement, three DS21T07’s would be needed at each end of the SCSI cable in order to terminate the
27 active signal lines.
DS21T16 BLOCK DIAGRAM
Figure 1
2 of 7
DS21T07
TYPICAL SCSI BUS CONFIGURATION
Figure 2
DS21T07
DS21T07
NOTES:
1. C1 = 4.7
µF
tantalum
C2 = 2.2
µF
tantalum or 4.7
µF
aluminum
2. If the DS21T07 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is that
recommended TERMPWR be derived from the SCSI cable, not generated locally. In this
configuration, if a power failure occurs in the peripheral, it will not affect the bus.
3. A high frequency bypass capacitor (0.1
µF
recommended) can be added in parallel to C1 for
applications using fast rise/fall time drivers.
3 of 7
DS21T07
PIN DESCRIPTION
Table 1
DS21T16E
PIN
1
DS21T16S
PIN
1
SYMBOL
TERMPWR1
DESCRIPTION
Termination Power 1.
Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2
µF or 4.7 µF. See Figure 2.
Signal Termination 1.
110 ohms termination.
Signal Termination 2.
110 ohms termination.
Signal Termination 3.
110 ohms termination.
Signal Termination 4.
110 ohms termination.
Signal Termination 5.
110 ohms termination.
Reference Voltage 1.
Must be externally connected
directly to the VREF2 pin. Must be decoupled with a 4.7
µF capacitor as shown in Figure 2.
Ground.
Signal ground; 0.0V.
Termination Power 2.
Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2
µF or 4.7 µF. See Figure 2.
Signal Termination 6.
110 ohms termination.
Signal Termination 7.
110 ohms termination.
Signal Termination 8.
110 ohms termination.
Signal Termination 9.
110 ohms termination.
No Connect.
Do not connect any signal to this pin.
Reference Voltage 2.
Must be externally connected
directly to the VREF1 pin. Must be decoupled with a 4.7
µF capacitor as shown in Figure 2.
Power Down.
When tied low, the DS21T07 enters a
power-down mode. Contains an internal 50K pullup.
Strap low to deactivate the DS21T07, leave open
circuited to activate the DS21T07.
Heat Sink Ground.
Internally connected to the
mounting pad. Should be either grounded or electrically
isolated from other circuitry.
3
4
5
6
7
9
2
3
4
5
6
7
R1
R2
R3
R4
R5
VREF1
10
11
8
9
GND
TERMPWR2
13
14
15
16
17
19
10
11
12
13
14
15
R6
R7
R8
R9
NC
VREF2
20
16
PD
2, 8,
12, 18
N/A
HS-GND
4 of 7
DS21T07
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 DS21T07 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 DS21T07 is not exposed to environmental stresses, such as burn-
in, 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
PD
Active
PD
Inactive
SYM
V
TP
V
PDA
V
PDI
MIN
4.00
-0.3
2.0
TYP
MAX
5.50
+0.8
V
TP
+ 0.3
(0°C to 70°C)
UNITS
V
V
V
NOTES
DC CHARACTERISTICS
PARAMETER
TERMPWR Current
Power-Down Current
Termination Resistance
Die Thermal Shutdown
Power-Down
Termination Capacitance
Input Leakage High
Input Leakage Low
SYMBOL
I
TP
I
TP
I
PD
R
TERM
T
SD
C
PD
I
IH
I
IL
MIN
TYP
5
100
110
150
MAX
250
8
150
112
3.0
-1.0
1.0
(0°C to 70°C)
UNITS
mA
mA
µA
ohms
°C
pF
µA
µA
NOTES
1, 3
1, 4
1, 2, 5
1, 2
1, 6
1, 2, 5, 6
1, 8
1, 7
108
150
REGULATOR CHARACTERISTICS
PARAMETER
Output Voltage
Drop Out Voltage
Output Current
Line Regulation
Load Regulation
Current Limit
Sink Current
SYMBOL
V
REF
V
DROP
I
OUT
LI
REG
LO
REG
I
LIM
I
SINK
MIN
2.79
TYP
2.85
0.50
1.0
1.3
350
200
MAX
2.93
0.75
25.2
2.0
3.0
(0°C to 70°C)
UNITS
V
V
mA
%
%
mA
mA
NOTES
1, 2
3, 6
9
1, 4
1, 3
1
1
5 of 7
京公网安备 11010802033920号
EEWORLD
