1
Linear Technology Chronicle •
November 1996
A Showcase of Linear Technology’s Focus Products
Linear Technology Chronicle
November 1996 Vol. 5 No. 11
Products of the Month
Software-Selectable Multiprotocol Chip Set
Simplifies Data Networking Interface Design
C-Load is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Controller IC Allows Safe Hot Swapping of Circuit Boards ..................................................... 2
First Dual 12-Bit Voltage Output DAC in SO-8 Runs on 3V Supply........................................ 2
Micropower Dual JFET Op Amps Feature pA Input Bias Currents and
C-LoadTM Drive Capability........................................................................................................ 3
Find Linear Technology’s Products on CD-ROM—Fast and Free!......................................... 4
Dual DAC Adds Features to Single 5V Supply, 12-Bit Family ................................................. 4
Inside This Issue:
Figure 1. The LTC1343 and LTC1344 Address the Problem of Easily Switching the
Terminations for Different Protocols Using a Single Connector. Here it is Configured
for Single Port DCE and V.35
NC
NC
CABLE
1343 F11
17
18
19
21
LTC1343
LTC1343
CONNECTOR
20
21
19
18
17
22
21
M2 M1
LTC1344
LATCH
M0 (DATA)
23 24 1
CTRL/CLK
22
(DATA)
M0
M1
M2
DCE/DTE
LATCH
20 CTRL/CLK
22
DCE/DTE
M2
M1
M0
(DATA)
LATCH
V
CC
DCE/
DTE
R1, 10k V
CC
R2, 10k V
CC
R3, 10k V
CC
R4, 10k V
CC
V.36 and X.21 protocols that are both NET1
and NET2 compliant. This chip set is ideal for
space limited networking applications and
supports all major telecom protocols for
remote access serial ports.
In a typical application, the first
LTC1343 is connected to the clock and data
signal lines along with the diagnostic LL
(local loop-back) and TM (test mode) signals.
The second LTC1343 is connected to the con-
trol signal lines along with the diagnostic RL
(remote loop-back) signals. Switching
between modes is simple—just three mode
select pins are required for both the LTC1343
and LTC1344, as shown in Figure 1. The
mode pins are latched internally to allow shar-
ing of the select lines between multiple
interface ports. DTE or DCE is set with one
pin, as is the designation for whether the
transceiver is used for data and clock signals
or control signals. This greatly simplifies the
task of switching eight different types of serial
ports to the same DB-25 connector, as shown
in Figure 2. Other routing tasks, such as loop-
back testing or echo clocking, are also easily
performed.
The LTC1343 is packaged in a 44-lead
SSOP and the LTC1344 in a 28-lead SSOP.
Together they eliminate the switches, relays
and jumpers normally required to switch
between drivers, receivers and associated ter-
mination schemes. The three chips together
occupy only 8 cm2 of board area, ideal for
space constrained applications. For a data
sheet and evaluation samples of this
multiprotocol chip set, contact your local
Linear Technology sales office.
Figure 2. Single 5V Complete
Multiprotocol Serial Port
The LTC
®
1343 multiprotocol trans-
ceiver and companion LTC1344 cable
terminator form a complete software-select-
able multiprotocol serial port, operating from
a single 5V supply. This is the first integrated
solution to pass the stringent NET1 and NET2
tests of the European Telecommunications
Institute.
The LTC1343 contains four drivers and
four receivers and the configuration logic to
do protocol selection, loopback testing as well
13 12 11 10 9 8 7 6 5 4 3 2
25 24 23 22 21 20 19 18 17 16 15 14
1
CLK AND DATA
DB-25
CONTROL
CLK AND
DATA
MODE
SELECT 3
LTC1343
RS232
EIA-530
EIA-530-A
RS449
V.35
V.36
X.21
LTC1343
LTC1344
CONTROL
as turning on and off the echo clock and the
low power shutdown mode. The LTC1343/
LTC1344 can be used in both DTE and DCE
equipment. The LTC1344 cable terminator
contains six switchable resistive terminations
to configure a single DB-25 connector for up
to eight different serial protocols. Two
LTC1343 transceivers and a single LTC1344
terminator form a DTE or DCE interface port,
capable of supporting RS232 (V.28), RS423
(V.10), EIA530, EIA530-A, RS449, V.35,
2
Linear Technology Chronicle •
November 1996
Controller IC Allows Safe
Hot Swapping of Circuit
Boards
The LTC1421 hot swap controller
safely limits the inrush currents that can
destroy components and traces on circuit
boards and prevents glitches that disrupt the
system bus when a circuit board is plugged
into a live backplane. The device can turn on
up to three board supply voltages at pro-
grammable rates. The LTC1421 is ideal for
backplanes and rack systems that must run
continuously or cannot tolerate glitches on
the supply rails when inserting or removing
circuit boards. It is appropriate for power
systems supplying 3V/5V, 5V/±12V or even
–48V/5V telecom voltages.
The key to controlling the inrush cur-
rent is the user-programmable power-up rate.
An external capacitor sets the timing for the
ramp-up of the positive FET voltages result-
ing in the switches being turned on slowly
and the current being held to an acceptable
level. A sense resistor in series with the
FETs, shown in Figure 1, is used to detect
excessive current levels. Both positive FETs
are ramped up at the same rate, with the
higher voltage FET kept above the lower
voltage FET to prevent power sequencing
problems.
The chip includes undervoltage lockout
and a voltage comparator to generate a reset
signal. Voltage levels can be monitored
using the uncommitted comparator and the
1.232V reference.
Power management functions include
data bus disable, reset input, system reset
and power good signals. During board inser-
tion or removal, the disable signal can be
used to halt the system bus by putting the
bus buffer in a high impedance state. The
reset input allows recycling the power with a
pushbutton or external signal. The reset out-
put and power good output signals are used
by the processor for general power manage-
ment functions.
The LTC1421 controller provides warn-
ing signals when power fails, the circuit
breaker has tripped or when the switches
have been turned off. Separate controls are
available for power-on reset or disabling the
data lines.
The LTC1421 is available in the
24-pin SO and SSOP packages. For a data
sheet and evaluation samples, contact your
local Linear Technology sales office.
Continued on page 3
First Dual 12-Bit Voltage
Output DAC in SO-8
Runs on 3V Supply
The LTC1446L is a dual 12-bit voltage
output digital-to-analog converter that is
complete with two rail-to-rail voltage output
amplifiers, a 1.22V bandgap voltage refer-
ence and a 3-wire cascadable serial interface,
all packed into an 8-pin SO package. The
maximum differential nonlinearity (DNL) is
only ±0.5LSB. It consumes just 2mW from
a single 3V supply making it the best solu-
tion for portable and battery-powered
equipment. Better than 12-bit monotonicity
over temperature makes the LTC1446L ideal
for feedback control applications such as
industrial control loops and general purpose
trim pots.
The 2.5V output voltage is guaranteed
even with a reduced supply of 2.7V. The
DAC outputs drive capacitive loads of up to
1000pF. Power-on reset insures the DACs
start in a known state after power up, easing
initial processor overhead. Figure 1 shows a
typical application for the LTC1446L.
The excellent typical differential non-
linearity (DNL) of 0.2LSB (Figure 2) not
only guarantees 12-bit monotonic perfor-
mance but also provides exceptional
performance in closed loop control systems.
The LTC1446L’s 3-wire serial interface
allows several dual DACs to be daisy-
10
9
14
13
8
11
15
6
7
RAMP
CPON
COMP
–
COMP
+
REF
FB
COMPOUT
PWRGD
RESET
2
24
4
3
1
CON2
AUXV
CC
FAULT
POR
CON1
V
CCLO
SETLO GATELO V
OUTLO
LTC1421
GND DISABLE
V
CCHI
SETHI GATEHI V
OUTHI
16 C2
0.1µF
C1
1µF
R5
16k
5%
Q1
MTB50N06E
R1
0.005Ω
171819202122
512
23
R3
1k
STAGGERED CONNECTOR
D1
R6
20k
1%
C3
220µF
R4
20k
5%
R7
7.15k
1%
Q2
1/2 Si4936DY
Q3
1/2 Si4936DY
C3
0.47µF
R2
0.025Ω
+
C5
220µF
V
EE
–12V
1A
V
DD
12V
1A
V
CC
5V
5A
+
C4
220µF
+
I/O
I/O
RESET
BEA
BEB
GND
1
13
12
µP
QS3384
QuickSwitch
®
QuickSwitch IS A REGISTERED TRADEMARK
OF QUALITY SEMICONDUCTOR CORPORATION.
1421 TA01
DATA BUS
PC BOARDBACKPLANE
DATA
BUS
GND
POR
FAULT
V
CC
V
DD
V
EE
V
CC
Figure 1. The LTC1421 Can Drive Three N-Channel MOSFETs That Switch the Power from the Backplane
to the Circuit Board. Resistors in Series with the Power FETs Sense Excessive Current Levels
3
Linear Technology Chronicle •
November 1996
Application of the Month
Micropower Dual JFET Op Amps Feature pA Input Bias Currents and C-Load Drive Capability
The LT
®
1462/LT1463 low input bias cur-
rents make them a natural for amplifying
low level signals from high impedance
transducers. The 1pA input bias current
contributes only 0.4fA/√Hz of current
noise or 0.4nV/√Hz voltage noise with a
1MΩ source impedance. A 1MΩ
impedance’s thermal noise of 130nV/√Hz
dominates the op amp’s noise, showing
that even with high source impedances, the
LT1462/LT1463 contribute very little to
total input-referred noise. Taking advan-
tage of these features, Figure 1’s
photodiode logging amplifier uses two
LT1462 duals or an LT1463 quad. Here, the
photodiode current is converted to a voltage
by the first op amp and D1 and amplified by
the first, second and third logarithmic com-
pression amplifiers. A DC feedback path
comprising R8, R9, C6 and Q1 is active only
for no-light conditions. Q1 is off when light
is present, isolating the photodiode from C6.
When feedback is needed, a small filtered
current through R8 prevents the op amp out-
puts from saturating when no signal is
present as shown in Figure 2.
The LT1462/LT1463 family is especially
suited for piezo transducer conditioning,
strain gauge weight scales, very low droop
track-and-holds, wide dynamic range pho-
todiode amplifiers and other applications
that benefit from pA input bias current. The
family also exhibits very low noise current,
important to circuits such as low frequency
filters. These op amps allow high value
resistors to be used with easily obtainable,
low value precision capacitors to set a
filter’s frequency characteristics without
compromising noise performance.
chained to save board space and is compat-
ible with SPI, QSPI and MICROWIRE
TM
protocols.
LTC1446L from page 2
Figure 1. This Logging Photodiode Amplifier Takes Advantage of the LT1462’s 1pA Input Bias
Current to Amplify the Low Level Signal from the Photodiode’s High Source Impedance
–
+
–
+
–
+
–
+
R13
10k
C4
10µF
R11
1M
AMP 4
1/2 LT1462 7
8
4
5
5V
–5V
6
R12
10k
R10
50k
R6
100k
D3
1N4148
R7
10M
R5
24k
AMP 3
1/2 LT1462
DC
OUT
C3
0.47µF
3
2
1
R3
100k
D2
1N4148
R4
10M
AMP 2
1/2 LT1462
AMP 1
1/2 LT1462 C2
200pF C5
200pF
R2
24k
7
5
6
2
3
8
4
1
5V
–5V
R1
100Ω
PHOTO-
DIODE
C1
1nF
D1
1N4148
R8
100k Q1
2N3904
C6
1µFR9
1M
DN136 F02
AC
OUT
Figure 2. Logging
Photodiode Amplifier
DC Output
PHOTODIODE CURRENT (A)
10
–11
10
–9
10
–7
10
–5
10
–3
AMP 3 DC OUTPUT (V)
–0.8
–1.0
–1.2
DN136 F03
–0.6
–0.4
0
–0.2
–1.6
–1.4
Figure 2. Typical Differential
Nonlinearity vs Input Code for
LTC1446L is Only ±0.2LSB.
Maximum DNL is ±0.5LSB
CODE
0
–0.5
DNL ERROR (LSB)
–0.4
–0.2
–0.1
0
0.5
0.2
1024 2048 2560
1446/46L G12
–0.3
0.3
0.4
0.1
512 1536 3072 3584 4095
The LTC1446L is available in 8-lead
SO and PDIP packages screened to the com-
mercial and industrial temperature ranges.
MICROWIRE is a trademark of National Semiconductor Corp.
Contact your local Linear Technology
sales office for a data sheet and evaluation
samples.
Figure 1. The LTC1446L Dual 12-Bit DAC is the First in an 8-Pin SO Package
to Operate with a Single 3V Supply
–
+
–
+
12-BIT
DAC B
LTC1446L: 3V TO 5V
LTC1446L: 1.22V
RAIL-TO-RAIL
VOLTAGE
OUTPUT
12-BIT
DAC A
POWER-ON
RESET
24-BIT
SHIFT
REG
AND
DAC
LATCH
µP
DIN
2
7
DOUT
4
61446/1446L TA01
CLK1
CS/LD3
8VOUT B
5VOUT A
4
Linear Technology Chronicle •
November 1996
© 1996 Linear Technology Corporation/Printed in USA
Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, California 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • For Literature Only: 1-800-4-LINEAR
Linear Technology
Products Are
Distributed By:
Almac/Arrow
Arrow/Schweber
Arrow/Zeus
Digi-Key
Electrosonic
Gerber Electronics
Farnell Electronics
Marshall Industries
Phase 1
Find Linear Technology’s
Products on CD-ROM—
Fast and Free!
LinearView
TM
is the easiest and quick-
est way of navigating over 8000 pages of
data sheets, Application Notes and Design
Notes in search of a particular topic or part
number. Powerful search engines are
employed for “key word” or “by parameter”
searching to select the best product for a par-
ticular application. LinearView is also handy
for design analysis, and includes LTC’s
popular design software programs, such as
SwitcherCAD
TM
and FilterCAD. It contains
all LTC product data sheets including those
that haveappeared in the 1990, 1992, 1994
and 1995 databooks and Design Notes. Also
included are all issues of Linear Technology
magazine. Familiar Windows
TM
appearance
and appealing organization of topics facili-
tate easy use by the PC user.
Try this new powerful tool and explore
what it can offer. A free copy of the
LinearView CD-ROM is yours for the ask-
ing. Contact your local Linear Technology
sales office.
Dual DAC Adds Features
to Single 5V Supply,
12-Bit Family
The LTC1454 is a dual 12-bit DAC
that consumes 3.5mW (typ) from a single
5V supply and has a differential nonlinearity
(DNL) of only ±0.5LSB. This makes it ideal
for feedback control applications such as
industrial control loops and general trim
pots. The low power consumption and high
integration make the LTC1454 an excellent
choice for portable or battery-powered
equipment.
The LTC1454 contains two 12-bit
DACs with rail-to-rail output amplifiers,
a 3-wire, cascadable serial interface and a
2.048V bandgap voltage reference. Offset
error is only ±18mV (max). The LTC1454
has an asynchronous Clear pin which resets
all DACs to zero scale. A unity/2X gain
select pin lets the user set the gain of the
output amplifiers. The on-chip reference is
available for external circuitry and is not
internally connected, allowing a user speci-
fied reference input.
The rail-to-rail amplifiers have
improved capacitive load handling over
competing devices and swing to 4.095V full
scale even when running on a 4.5V supply.
The serial I/O is cascadable which reduces
interface hardware when multiple DACs are
used. Power-on reset insures the DACs start
in a known state after power up and Clear
resets the DAC to zero scale asynchro-
nously. For a data sheet and evaluation
samples of this high performance ADC,
contact your local Linear Technology
sales office.
LinearView and SwitcherCAD are trademarks of Linear
Technology Corporation.
Windows is a trademark of Microsoft Corporation.
X1/X2 B
X1/X2 A
D
IN
CLK
D
OUT
V
CC
POWER-ON
RESET
–
+
12-BIT
DAC A
12-BIT
DAC B
REFOUT
CS/LD
V
OUT B
REFHI B
REFHI A
REFLO GND
14
16
1
11
8
7
12
2
6
5
3
4
9, 15
LTC1454: 5V
LTC1454L: 3V TO 5V LTC1454: 2.048V
LTC1454L: 1.22V
10
13
V
OUT A
–
+
CLR
1454 BD02
24-BIT
SHIFT
REG
AND
DAC
LATCH
µP
Figure 1. LTC1454 Dual 12-Bit Rail-to-Rail DAC Offers Many Features
in Its 16-pin SO Package.
