ETC DS21S07A

DS21S07A
DS21S07A
SCSI Terminator
FEATURES
• Fully
PIN ASSIGNMENT
compliant with SCSI–1, Fast SCSI and Ultra
TERMPWR1
1
16
PD
R1
2
15
VREF2
R2
3
14
NC
R3
4
13
R9
R4
5
12
R8
R5
6
11
R7
VREF1
7
10
R6
GND
8
9
SCSI
• Backward compatible to the DS2107 and DS2107A
• Provides active termination for nine signal lines
• Laser–trimmed 110
ohm termination resistors have
2% tolerance
• Low dropout voltage regulator
• Power–down
TERMPWR2
DS21S07AS 16–PIN SOIC (300 MIL)
mode isolates termination resistors
from the bus
• SCSI bus hot plug–compatible
TERMPWR1
1
20
PD
HS–GND
2
19
VREF2
R1
3
18
HS–GND
R2
4
17
NC
R3
5
16
R9
R4
6
15
R8
R5
7
14
R7
HS–GND
8
13
R6
VREF1
9
12
HS–GND
10
11
TERMPWR2
• Fully supports actively negated SCSI signals
• Onboard thermal shutdown circuitry
• 16–pin plastic SOIC (DS21S07AS) and 20–pin plastic
TSSOP (Thin Shrink Small Outline Package)
(DS21S07AE)
GND
DS21S07AE 20–PIN TSSOP (173 MIL)
ACTUAL FOOTPRINT SIZE
.41”
.26”
.27”
.41”
DS21S07AS
DS21S07AE
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 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, in-
trinsic TERMPWR decoupling, and very low quiescent
current consumption. The DS21S07A integrates a regulator and nine precise switched 110 ohm termination
resistors into a monolithic IC. The DS21S07A can be
electrically isolated from the SCSI bus without physical
removal from the SCSI device.
022798 1/7
DS21S07A
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 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
VREF will move less than 60 mV. When all lines settle in
the quiescent state, the regulator will consume about
2.5 mA. When the DS21S07A 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 DS21S07A from the signal lines and effectively
remove it from the circuit. The power–down pin (PD)
has an internal 50KΩ pull–up 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. 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
(“A” Cable), two DS21S07A’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
(“P” Cable), three DS21S07A’s would be needed at
each end of the SCSI cable in order to terminate the 27
active signal lines.
DS21S07A BLOCK DIAGRAM Figure 1
PD
TERMPWR1
TERMPWR2
50K Ohm
Power
Down
Circuitry
110 Ohms
R1
110 Ohms
R2
Bandgap
Reference
110 Ohms
R3
+
–
110 Ohms
R4
110 Ohms
R5
110 Ohms
R6
GND
110 Ohms
R7
110 Ohms
R8
110 Ohms
R9
VREF1
VREF2
022798 2/7
DS21S07A
TYPICAL SCSI BUS CONFIGURATION Figure 2
Termination Power Line
DS21S07A
C1
+
+
C2
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
SCSI
Cable
R8 R9
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
DS21S07A
C1
+
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1 R2
R9
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
NOTES:
1. C1 = 4.7 µF tantalum
C2 = 2.2 µF tantalum or 4.7 µF aluminum
2. If the DS21S07A 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.
022798 3/7
DS21S07A
PIN DESCRIPTION Table 1
DS21S07AE
PIN
DS21S07AS
PIN
SYMBOL
DESCRIPTION
1
1
TERMPWR1
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.
3
2
R1
Signal Termination 1. 110 ohm termination.
4
3
R2
Signal Termination 2. 110 ohm termination.
5
4
R3
Signal Termination 3. 110 ohm termination.
6
5
R4
Signal Termination 4. 110 ohm termination.
7
6
R5
Signal Termination 5. 110 ohm termination.
9
7
VREF1
10
8
GND
11
9
TERMPWR2
13
10
R6
Signal Termination 6. 110 ohm termination.
14
11
R7
Signal Termination 7. 110 ohm termination.
15
12
R8
Signal Termination 8. 110 ohm termination.
16
13
R9
Signal Termination 9. 110 ohm termination.
17
14
NC
No Connect. Do not connect any signal to this pin.
19
15
VREF2
20
16
PD
2, 8, 12, 18
N/A
HS–GND
022798 4/7
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.
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 DS21S07A enters a powerdown mode. Contains an internal 50K pull–up. Strap low to deactivate the DS21S07A, leave open circuited to activate the
DS21S07A.
Heat Sink Ground. Internally connected to the mounting pad.
Should be either grounded or electrically isolated from other circuitry.
DS21S07A
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.
(0°C to 70°C)
RECOMMENDED OPERATING CONDITIONS
PARAMETER
SYMBOL
MIN
VTP
4.00
PD Active
VPDA
PD Inactive
VPDI
TERMPWR Voltage
TYP
MAX
UNITS
5.50
V
–0.3
+0.8
V
2.0
VTP +0.3
V
(0°C to 70°C)
DC CHARACTERISTICS
PARAMETER
NOTES
SYMBOL
TERMPWR Current
MIN
ITP
ITP
Power Down Current
IPD
Termination Resistance
RTERM
108
Die Thermal Shutdown
TSD
150
Power Down Termination
Capacitance
CPD
Input Leakage High
IIH
Input Leakage Low
IIL
TYP
MAX
UNITS
NOTES
2.5
250
5
mA
mA
1, 3
1, 4
100
150
µA
1, 2, 5
110
112
ohms
1, 2
°C
1, 6
pF
1, 2, 5, 6
µA
1, 8
1.0
µA
1, 7
3.0
5.0
–1.0
(0°C to 70°C)
REGULATOR CHARACTERISTICS
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Output Voltage
VREF
2.79
2.85
2.93
V
1, 2
Drop Out Voltage
VDROP
0.50
0.75
V
3, 6
Line Regulation
LIREG
1.0
2.0
%
1, 4
Load Regulation
LOREG
1.3
3.0
%
1, 3
Current Limit
ILIM
350
mA
1
Sink Current
ISINK
mA
1
200
022798 5/7
DS21S07A
NOTES:
1. 4.00V < TERMPWR < 5.50V.
2. 0.0V < signal lines < TERMPWR.
3. All signal lines = 0.0V.
4. All signal lines open.
5. PD = 0.0V.
6. Guaranteed by design; not production tested.
7. R1 through R9 only.
8. R1 through R9 and PD.
DS21S07AS SCSI TERMINATOR 16–PIN SOIC (300 MIL)
K
G
PKG
B
1
H
16–PIN
DIM
MIN
MAX
A IN.
MM
0.402
10.21
0.412
10.46
B IN.
MM
0.290
7.37
0.300
7.65
C IN.
MM
0.089
2.26
0.095
2.41
E IN.
MM
0.004
0.102
0.012
0.30
F IN.
MM
0.094
2.38
0.105
2.68
A
C
G IN.
MM
E
F
phi
J
022798 6/7
0.050 BSC
1.27 BSC
H IN.
MM
0.398
10.11
0.416
10.57
J IN.
MM
0.009
0.229
0.013
0.33
K IN.
MM
0.013
0.33
0.019
0.48
L IN.
MM
0.016
0.40
0.040
1.02
phi
0°
8°
L
DS21S07A
DS21S07AE SCSI TERMINATOR 20–PIN TSSOP
D
n
E
H
SEE DETAIL A
c
B
e1
A2
A
A1
phi
G
L
DETAIL A
DIM
MIN
A MM
–
1.10
A1 MM
0.05
–
A2 MM
0.75
1.05
C MM
0.09
0.18
L MM
0.50
0.70
e1 MM
MAX
0.65 BSC
B MM
0.18
0.30
D MM
6.40
6.90
E MM
4.40 NOM
G MM
0.25 REF
H MM
phi
6.25
6.55
0°
8°
022798 7/7