MAXIM DS2119M Technical data

r

查询DS2119M供应商

Ultra3 LVD/SE SCSI Terminato

DS2119M

www.maxim-ic.com

FEATURES

Fully compliant with SCSI SPI-2, SPI-3,

SPI-4, Ultra160, and Ultra320

Provides multimode low-voltage

differential/single-ended (LVD/SE)
termination for nine signal-line pairs

Auto-selection of LVD or SE termination
5% tolerance on SE and LVD termination

resistance

Low power-down capacitance of 3pF
Onboard thermal-shutdown circuitry
SCSI-bus hot-plug compatible
Fully supports actively negated SE SCSI

signals

PIN ASSIGNMENT

VREF

RIP

RIN
R2P
R2N

HS GND

R3P

R3N

R4P
R4N
R5P
R5N

ISO

GND

1
2
3

4
5
6
7
8
9
10
11
12
13
14

DS2119ME 28-Pin TSSOP

28
27
26
25
24
23
22
21
20
19
18
17
16
15

TPWR

TPWR
R9N
R9P
R8N
R8P
HS GND
R7N
R7P
R6N
R6P
DIFF_CAP
DIFFSENSE
MSTR/SLV

DESCRIPTION

The DS2119M Ultra3 LVD/SE SCSI Terminator is both a low-voltage differential (LVD) and single­ended (SE) terminator. The multimode operation enables the designer to implement LVD in current
products while allowing the end-user SE-backward compatibility with legacy devices. If the device is
connected in an LVD-only bus, the DS2119M will use LVD termination. If any SE devices are connected
to the bus, the DS2119M will use SE termination. This is accomplished automatically inside the part by
sensing the voltage on the SCSI bus DIFFSENS line.

For the LVD termination, the DS2119M integrates two current sources with nine precision resistor
strings. For the SE termination, one regulator and nine precision 110Ω resistors are used. Three
DS2119M terminators are needed for a wide SCSI bus.

REFERENCE DOCUMENTS

Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface (SPI) Project: 0855-M, 1995
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 2 (SPI-2) Project: 1142-M, 1998
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 3 (SPI-3) Project: 1302-D, 1999
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 4 (SPI-4) Project: 1365-D, 200x

Available From:

American National Standards Institute (ANSI) Phone: [phone]
Global Engineering Documents 15 Inverness Way East; Englewood, CO 80112 Phone: [phone]

1 of 9 022002

DS2119M

FUNCTIONAL DESCRIPTION

The DS2119 combines LVD and SE termination with DIFFSENS sourcing and detection.

A bandgap reference is fed into two amplifiers, which creates a 1.25V reference voltage and a 2.85V
reference voltage. The control logic determines which of these references will be applied to the
termination resistors. If the SCSI bus is in LVD mode, then the 1.25V reference will be used. If the SCSI
bus is in SE mode, then the 2.85V reference will be used. That same control logic will switch in/out
parallel resistors to change the total termination resistance accordingly. Finally, in SE mode, the Rp pins
will be switched to ground.

The DIFFSENSE circuitry decodes trinary logic. There will be one of three voltages on the SCSI control
line called DIFFSENS. Two comparators and a NAND gate determine if the voltage is below 0.6V, above

2.15V, or in between. That indicates the mode of the bus to be SE, HVD, or LVD, respectively.

The DS2119M’s DIFF_CAP pin monitors the DIFFSENS line to determine the proper operating mode of
the device. The DIFFSENSE pin can also drive the SCSI DIFFSENS line (when MSTR/SLV = 1) to
determine the SCSI bus-operating mode. The DS2119M switches to the termination mode that is
appropriate for the bus based on the value of the DIFFSENS voltage. These modes are:

LVD Mode: LVD termination is provided by a precision laser-trimmed resistor string with two

current sources. This configuration yields a 105Ω differential and 150Ω common-mode
impedance. A fail-safe bias of 112mV is maintained when no drivers are connected to the SCSI
bus.

SE Mode: When the external driver for a given signal line turns off, the active terminator will pull

that signal line to 2.85V (quiescent state). When used with an active negation driver, the power
amp can sink 22mA per line and the reference voltage will move less than 100mV. The

terminating resistors maintain their 110Ω=value.

HVD Isolation Mode: The DS2119M identifies that there is an HVD (high-voltage differential)

device on the SCSI bus and isolates the termination pins from the bus.

When ISO = 1, the termination pins are isolated from the SCSI bus, V
shutdown, the termination pins are isolated from the SCSI bus and V
DIFFSENSE driver is shut down during either of these two events.

To ensure proper operation, the TPWR pin should be connected to the SCSI bus TERMPWR line. As
with all analog circuitry, the TERMPWR and V

lines should be bypassed locally. A 2.2µF capacitor

DD

and a 0.01µF high-frequency capacitor are recommended between TPWR and ground and placed as close

as possible to the DS2119M. The DS2119M should be placed as close as possible to the SCSI connector
to minimize signal and power-trace length, thereby resulting in less input capacitance and reflections,
which can degrade the bus signals.

remains active. During thermal

REF

becomes high impedance. The

REF

2 of 9

DS2119M

To maintain the specified regulation, a 4.7µF capacitor is required between the V

pin (VREF) and

REF

ground of each DS2119M. A high frequency cap (0.1µF ceramic recommended) can also be placed on the

V

pin in applications that use fast rise/fall time drivers. A typical SCSI bus configuration is shown in

REF

Figure 2.

DIFFSENS Noise Filtering: The DS2119M incorporates a digital filter to remove high-frequency

transients on the DIFFSENS control line, thereby eliminating erroneous switching between
modes. This filter eliminates the need for the external capacitor and resistor, which heretofore
performed this function.

NOTES:

1) DIFFSENS. Refers to the SCSI bus signal.

2) DIFFSENSE. Refers to the Dallas Semiconductor pin name and internal circuitry relating the
DIFFSENS driver.

3 of 9

Figure 1. DS2119M BLOCK DIAGRAM

DS2119M

4 of 9

Figure 2. SCSI BUS CONFIGURATION

DS2119M

5 of 9

DS2119M

Table 1. PIN DESCRIPTION

PIN SYMBOL DESCRIPTION

1 VREF Reference Voltage. 2.85V reference in SE mode and 1.25V reference in

LVD mode; must be decoupled with a 4.7µF cap.

2–5, 7–12,

18–21, 23–26

RxP,
RxN

Signal Termination. Connect to SCSI bus signal lines.

6, 22 HS GND Heat Sink Ground. Internally connected to the mounting pad. Should

be grounded.

13 ISO Isolation. When pulled high, the DS2119M isolates its bus pins (RxP,

RxN) from the SCSI bus.

14 GND Ground. Signal ground; 0V.
15 MSTR/SLV Master/Slave. Mode-select for the noncontrolling terminator. When

pulled high, MSTR enables the DIFFSENSE driver.

16 DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line.
17 DIFF_CAP DIFFSENSE CAPACITOR. Connect a 0.1µF capacitor for

DIFFSENSE filter. Input to detect the type of device (differential or
single-ended) on the SCSI bus.

27, 28 TPWR Termination Power. Connect to the SCSI TERMPWR line and

decouple with a 2.2µF capacitor.

RECOMMENDED OPERATING CONDITIONS

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Termpower Voltage
SE Mode
LVD Mode

V
Logic 0 VIL -0.3 +0.8 V
Logic 1 VIH 2.0 V
Operating Temperature V

V

TPWR

TPWR

(SE)

(LVD)

0 70 °C

AMB

4.0

2.7

5.5

5.5

+ 0.3 V

TPWR

V
V

6 of 9

DS2119M

SINGLE-ENDED CHARACTERISTICS

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

SE Termination

RSE 104.5 110 115.5 Ω 1
Resistance
SE Voltage Reference V
SE Output Current l
Output Capacitance C

2.7 2.85 3.0 V

REF

25.4 mA 2

OSE

3 pF 3

OUT

LOW-VOLTAGE DIFFERENTIAL CHARACTERISTICS

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Differential Mode
Termination Resistance
Common Mode
Termination Resistance

RDM 100

RCM 110

110 Ω

190

Ω
Differential Mode Bias VDM 100 125 mV 4
Common Mode Bias VCM 1.125 1.375 V

DC CHARACTERISTICS

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Termpower Current I
Input Leakage High IIH -1.0 µA
Input Leakage Low IIL 1.0 µA
Output Current High IOH -1.0 mA 5, 7
Output Current Low IOL 4.0 mA 6, 7
DIFFSENS SE
Operating Range
DIFFSENS LVD
Operating Range
DIFFSENS HVD
Operating Range

V

V

DIFFSENSE Driver
Output Voltage
DIFFSENSE Driver
Source Current
DIFFSENSE Driver
Sink Current
Thermal Shutdown 150 ºC 3

12 mA 4

TPMR

V

-0.3 0.5 V

SEOR

0.7 1.9 V

LVDOR

2.4 V

HVDOR

V

1.2 1.4 V 8, 9

DSO

5 15 mA 8, 10, 12

I

DSH

20 200 µA 8, 11

I

DSL

+ 0.3 V

TPWR

7 of 9

DS2119M

REGULATOR CHARACTERISTICS (0°C to +70°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Line Regulation LI
Load Regulation LO
Current Limit I
Sink Current I

NOTES:

1) V

2) V

3) Guaranteed by design.

4) All lines open.

5) V

6) V

7) SE/LVD/HVD pins only.

8) MSTR/SLV = 1.

9) I

10) V

11) V

12) TPWR = 5.5V.

= 0V to 3V.

LINE

= 0.2V.

LINE

= 2.4V.

OUT

= 0.4V.

OUT

= 0mA to 5mA.

DS

= 0V.

DSO

= 2.75V.

DSO

1.0 2.5 %

REG

1.3 3.5 %

REG

550 mA

LIM

200 mA

SINK

8 of 9

DS2119M 28-PIN SSOP PACKAGE

R

R

DS2119M

NOTES:

1) DIMENSION “D” DOES NOT INCLUDE MOLD MISMA TCH, FLASH, O

PROTRUSIONS. MOLD MISMATCH, FLASH, AND PROTRUSIONS
SHALL NOT EXC EED 0.15 PER SIDE.

2) DIMENSION “B” DOES NOT INCLUDE DAMBAR PROTRUSION.

DAMBAR PROTRUSION SHALL NOT BE LOCATED ON THE LOWE
RADIUS OF THE FOOT.

PKG 28-PIN

DIM MIN MAX

A

MM

A1

MM

A2

MM

c

MM

L

MM

e1

MM

b

MM

D

MM

E1

MM

E

MM

- 1.10

0.05 -

0.75 1.05

0.09 0.20

0.50 0.75

0.65 BSC

0.18 0.30

9.60 9.80

4.40 BSC

6.20 6.60

9 of 9