DS21S07A
SCSI Terminator
www.maxim-ic.com
GENERAL DESCRIPTION
PIN CONFIGURATIONS
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 DS21S07A 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
DS21S07A integrates a regulator and nine precise
switched 110Ω termination resistors into a
monolithic IC. The DS21S07A can be electrically
isolated from the SCSI bus without physical removal
from the SCSI device.
FEATURES
Fully Compliant with SCSI-1, Fast SCSI, and
Ultra SCSI
Backward Compatible to the DS2107 and
DS2107A
Provides Active Termination for Nine Signal
Lines
ACTUAL FOOTPRINT SIZE
0.41"
Laser-Trimmed 110Ω Termination Resistors
Have 2% Tolerance
Low Drop-Out Voltage Regulator
Power-Down Mode Isolates Termination
Resistors from the Bus
SCSI Bus Hot Plug Compatible
Fully Supports Actively Negated SCSI Signals
On-Board Thermal Shutdown Circuitry
16-Pin Plastic SO (DS21S07AS) and 20-Pin
Plastic TSSOP (Thin Shrink Small Outline
Package) (DS21S07AE)
0.41"
0.26"
0.27"
DS21S07AS
DS21S07AE
ORDERING INFORMATION
VOLTAGE
(V)
DS21S07AS
5
DS21S07AS+
5
DS21S07AS/T&R
5
DS21S07AS+T&R
5
DS21S07AE
5
DS21S07AE/T&R
5
PART
PINPACKAGE
16 SO
16 SO
16 SO
16 SO
20 TSSOP
20 TSSOP
TOP
MARK
DS21T07S
DS21T07S
DS21T07S
DS21T07S
DS21T07E
DS21T07E
+ Denotes lead-free package. The top mark includes a “+" on
lead-free packages.
Note: All devices are specified over the 0°C to +70°C operating
temperature range.
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REV: 022106
DS21S087A
FUNCTIONAL DESCRIPTION
The DS21S07A consists of a bandgap reference, buffer amplifier, and nine termination resistors
(Figure 1). The bandgap reference circuit produces a precise 2.55V level that is fed to a buffer amplifier.
The buffer produces a 2.85V level and can source at least 24mA 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 pulls
the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals, the buffer can sink at
least 200mA, and VREF will move less than 60mV. When all lines settle in the quiescent state, the
regulator consumes about 2.5mA. When the DS21S07A is put into power-down mode by bringing PD
low, the power-down circuitry turns off the transistors on each signal line. This isolates the DS21S07A
from the signal lines and effectively removes it from the circuit. The power-down pin (PD) has an internal
50kΩ pullup resistor. To place the DS21S07A into an active state, the PD pin should be left open
circuited. When installed on disk drives or RAID system components, the DS21S07A 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
DS21S07A requires a 4.7µF capacitor connected between the VREF pins and ground. Figure 2 details a
typical SCSI bus configuration. In an 8-bit-wide SCSI bus arrangement (“A” Cable), two DS21S07A’s
would be needed at each end of the SCSI cable to terminate the 18 active signal lines. In a 16-bit-wide
SCSI bus arrangement (“P” Cable), three DS21S07A’s would be needed at each end of the SCSI cable to
terminate the 27 active signal lines.
Figure 1. DS21S087A Block Diagram
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DS21S087A
Figure 2. Typical Differential SCSI Bus Configuration
NOTE 1: C1 = 4.7µF TANTALUM CAPACITOR; C2 = 2.2µF TANTALUM OR 4.7µF ALUMINUM CAPACITOR.
NOTE 2: IF THE DS21S07A IS TO BE EMBEDDED INTO A PERIPHERAL THAT WILL ACT AS A TARGET
ON A SCSI BUS, IT IS RECOMMENDED THAT 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.
NOTE 3: A HIGH-FREQUENCY BYPASS CAPACITOR (0.1µF RECOMMENDED) CAN BE ADDED IN
PARALLEL TO C1 FOR APPLICATIONS USING FAST RISE/FALL TIME DRIVERS.
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DS21S087A
Table 1. Pin Description
PIN
TSSOP
SO
NAME
1
1
TERMPWR1
2, 8, 12,
18
—
HS-GND
3–7,
13–16
2–6,
10–13
R1–R9
9
7
VREF1
10
8
GND
11
9
TERMPWR2
17
14
NC
19
15
VREF2
20
16
PD
FUNCTION
Termination Power 1. Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2µF
capacitor or 4.7µF capacitor. See Figure 2.
Heat Sink Ground. Internally connected to the mounting pad.
Should be either grounded or electrically isolated from other
circuitry.
Signal Termination 1–9. 110Ω termination.
Reference Voltage 1. Must be externally connected directly to
the VREF2 pin. Must be decoupled with a 4.7µF capacitor as
shown in Figure 2.
Ground. 0V, signal ground.
Termination Power 2. Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2µF
capacitor or 4.7µF capacitor. See Figure 2.
No Connection. 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 4.7µF capacitor as
shown in Figure 2.
Active-Low Power-Down. When tied low, the DS21S07A
enters a power-down mode. Contains an internal 50kΩ pullup
resistor. Strap low to deactivate the DS21S07A; leave open
circuited to activate the DS21S07A
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DS21S087A
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to Ground……………………………………………..-1.0V to +7.0V
Operating Temperature Range………………………………………………………………..0°C to +70°C
Storage Temperature Range………………………………………………………………-55°C to +125°C
Soldering Temperature………………………………………….See IPC/JEDEC J-STD-020 Specification
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 device
reliability.
RECOMMENDED OPERATING CONDITIONS
(TA = 0°C to +70°C)
PARAMETER
TERMPWR Voltage
PD Active
PD Inactive
SYM
VTP
VPDA
VPDI
MIN
4.00
-0.3
2.0
TYP
MAX
5.50
+0.8
VTP + 0.3
UNITS
V
V
V
NOTES
MIN
TYP
2.5
100
110
MAX
250
5
150
112
UNITS
mA
mA
µA
Ω
ºC
NOTES
1, 3
1, 4
1, 2, 5
1, 2
1, 6
3.0
5.0
pF
1, 2, 5, 6
1.0
µA
µA
1, 8
1, 7
UNITS
V
V
%
%
mA
mA
NOTES
1, 2
3, 6
1, 4
1, 3
1
1
DC CHARACTERISTICS
(TA = 0°C to +70°C)
PARAMETER
TERMPWR Current
Power-Down Current
Termination Resistance
Die Thermal Shutdown
Power-Down Termination
Capacitance
Input Leakage High
Input Leakage Low
SYMBOL
ITP
IPD
RTERM
TSD
108
150
CPD
IIH
IIL
-1.0
REGULATOR CHARACTERISTICS
(TA = 0°C to +70°C)
PARAMETER
Output Voltage
Drop-Out Voltage
Line Regulation
Load Regulation
Current Limit
Sink Current
SYMBOL
VREF
VDROP
LIREG
LOREG
ILIM
ISINK
MIN
2.79
200
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TYP
2.85
0.50
1.0
1.3
350
MAX
2.93
0.75
2.0
3.0
DS21S087A
NOTES:
1)
2)
3)
4)
5)
6)
7)
8)
4.00V < TERMPWR < 5.50V.
0.0V < signal lines < TERMPWR.
All signal lines = 0V.
All signal lines open.
PD = 0V.
Guaranteed by design; not production tested.
R1 to R9 only.
R1 to R9 and PD.
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DS21S087A
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline
information, go to www.maxim-ic.com/DallasPackInfo.)
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DS21S087A
PACKAGE INFORMATION (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline
information, go to www.maxim-ic.com/DallasPackInfo.)
8 of 8
Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product.
No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
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© 2006 Maxim Integrated Products • Printed USA
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