Datasheet DS2107A Datasheet (dallas semiconductor)

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DS2107A

SCSI Terminator

FEATURES

• Fully compliant with SCSI and SCSI-2 standards

• Backward compatible to the DS2107S

• Provides active termination for 9 signal lines

• Laser-trimmed 110 ohm termination resistors have

1% tolerance

• Low dropout voltage

• Power-down mode isolates termination resistors from

the bus

• Handles actively negated SCSI signals

• Onboard thermal shutdown circuitry

• 16-pin plastic SOIC (DS2107AS) and 20-pin plastic

thin SSOP (DS2107AE)

PIN ASSIGNMENT

TERMPWR1

VREF1

GND

TERMPWR1

HS–GND

VREF1

GND

1 2

R1 R2

4 5

R4 R5

6 7 8

DS2107AS 16-Pin SOIC (300 mil)

1 2

7 8 9 10 11

DS2107AE 20-Pin TSSOP (173 mil)

ACTUAL FOOTPRINT SIZE

.41”

16 15 14 13 12

20 19 18 17 16 15 14 13

PD VREF2

NC R9 R8 R7 R6 TERMPWR2

PD VREF2

HS–GND NC R9

R8 R7 R6

HS–GND TERMPWR2

.26”

DESCRIPTION

The SCSI-2 standard recommends the use of active terminations at both ends of every cable segment in a SCSI system with single-ended drivers and receivers. The DS2107A SCSI T erminator , which is fully compliant with the standard, enables the designer to gain the benefits of active termination: greater immunity to voltage drops on the TERMPWR (TERMination PoWeR)

.41”

.27”

DS2107AS DS2107AE

line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2107A integrates a regulator and nine precise switched 110 ohm termination resistors into a monolithic IC.

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DS2107A

FUNCTIONAL DESCRIPTION

The DS2107A 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 200 mA. When all lines settle in the quiescent state, the regulator will consume about 5 mA. When the DS2107A is put into powerdown mode by bringing PD

low, the power-down circuitry will turn off the transistors on each signal line. This will isolate the DS2107A from the signal lines and effectively remove it from the circuit. The power-down pin (PD)

DS2107A BLOCK DIAGRAM Figure 1

TERMPWR1 TERMPWR2

GND

Bandgap

Reference

50K Ohm

has an internal 50K ohm pull-up resistor. To place the DS2107A into an active state, the PD

pin should be left

open circuited.

T o 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 DS2107A requires parallel 0.1 µF and 4. 7 µF capacitors 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 DS2107A’ 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 DS2107A’s would be needed at each end of the SCSI cable in order to terminate the 27 active signal lines.

Power

Down

Circuitry

110 Ohms

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VREF1 VREF2

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TYPICAL SCSI BUS CONFIGURATION Figure 2

Termination Power Line

DS2107A

C1 C2

DS2107A

TERMPWR1 TERMPWR2

VREF1

VREF2

GND

R1 R2R9

SCSI Bus Transceiver

SCSI Cable

C1 C2

SCSI Bus Transceiver

DS2107A

TERMPWR1 TERMPWR2

VREF1

VREF2

GND

R1 R9

SCSI Bus Transceiver

NOTES:

1. C1 = 0.1µF ceramic C2 = 4.7µF tantalum C3 = 2.2 µF tantalum or 4.7 µF aluminum

2. If the DS2107A 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.

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DS2107A

PIN DESCRIPTION Table 1

DS2107AE

1 1 TERMPWR1 Termination Power 1. Should be connected to the SCSI

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 Reference Voltage 1. Must be externally connected directly to

10 8 GND Ground. Signal ground; 0.0V . 11 9 TERMPWR2 Termination Power 2. Should be connected to the SCSI

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 Reference Voltage 2. Must be externally connected directly to

20 16 PD Power Down. When tied low, the DS2107A enters a power-down

2,8,12,18 N/A HS–GND Heat Sink Ground. Internally connected to the mounting pad.

DS2107AS

SYMBOL DESCRIPTION

TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF. See Figure 2.

the VREF2 pin. Must be decoupled with a 4.7µF and a 0.1µF as shown in Figure 2.

TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF. See Figure 2.

the VREF1 pin. Must be decoupled with a 4.7µF and a 0.1µF as shown in Figure 2.

mode. Contains an internal 50K pull-up. Strap low to deactivate the DS2107A, leave open circuited to activate the DS2107A.

Should be either grounded or electrically isolated from other circuitry.

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DS2107A

ABSOLUTE MAXIMUM RATINGS*

Voltage on Any Pin Relative to Ground -1.0V to +7.0V Operating Temperature 0°C to +70°C Storage Temperature -55°C to 125°C Soldering Temperature 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 SYMBOL MIN TYP MAX UNITS NOTES

TERMPWR Voltage V PD Active V PD Inactive V

PDA

PDI

4.00 5.25 V

-0.3 0.8 V

2.0 VTP +0.3 V

DC CHARACTERISTICS (0°C to 70°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

TERMPWR Current I

Power Down Current I T ermination Resistance R Die Thermal Shutdown T Power Down Termination

Capacitance PD Hysteresis H

TERM

100 µA 1,2,5

108 110 112 ohms 1,2

150 °C 1

8.5 10 pF 1,2,5,6

280 mV 1

250

mA mA

1,3 1,4

REGULATOR CHARACTERISTICS (0°C to 70°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Output Voltage V Drop Out Voltage V Line Regulation LI Load Regulation LO Current Limit I Sink Current I

REF

DROP

REG

LIM

SINK

2.79 2.85 2.91 V 1,2

0.75 1.0 V 3,6

1.0 2.0 % 1,4,6

1.3 3.0 % 1,2,6

300 350 400 mA 1

200 mA 1

NOTES:

1. 4.00V < TERMPWR < 5.25V .

2. 0.0V < signal lines < 3.0V .

3. All signal lines = 0.0V .

4. All signal lines open.

5. PD

= 0.0V.

6. Guaranteed by design; not production tested.

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DS2107A

DS2107AS SCSI TERMINATOR 16-PIN SOIC (300 MIL)

16-PINPKG

DIM MIN MAX

A IN.

0.402

10.21

0.290

7.37

0.089

2.26

0.004

0.102

0.094

2.38

0.050 BSC

1.27 BSC

0.398

10.11

0.009

0.229

0.013

0.33

0.40 0° 8°

0.412

10.46

0.300

7.65

0.095

2.41

0.012

0.30

0.105

2.68

0.416

10.57

0.013

0.33

0.019

0.48

0.040

1.02

B IN.

C IN.

E IN.

F IN.

G IN.

H IN.

J IN.

K IN.

L IN.MM0.016

phi

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DS2107AE SCSI TERMINATOR 20-PIN TSSOP (PRELIMINARY)

DS2107A

DIM MIN MAX

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 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 6.25 6.55

phi 0° 8°

SEE DETAIL A

DETAIL A

phi

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