Linear Technology Magazine • February 1995
39
New Device Cameos
NEW DEVICE CAMEOS
Burst Mode
TM
and SafeSlot
TM
are trade-
marks of Linear Technology Corporation.
, LTC
and LT
are registered trademarks
used to identify products of Linear
Technology Corp. Other product names may
be trademarks of the companies that
manufacture the products.
Information furnished by Linear Technol-
ogy Corporation is believed to be accurate
and reliable. However, Linear Technology
makes no representation that the circuits
described herein will not infringe on existing
patent rights.
input operating-voltage range with
minimal supply currents. Under a
no-load condition, the LTC1574 draws
only 130µA. In shutdown mode, it
draws a mere 2µA, making this con-
verter ideal for battery powered
applications. In dropout mode, the
internal P-channel MOSFET switch
turns on continuously, providing ex-
tremely low dropout specifications
(better than those of most linear regu-
lators). This allows the user to
maximize the life of the battery.
The LTC1574 step-down converter
is designed specifically to eliminate
noise at audio frequencies, while
maintaining high efficiency at low
output currents. The internal switch
is current controlled at a peak of
approximately 340mA or 600mA, se-
lectable by a control pin. Low peak
switch current is one of the key fea-
tures that allow the LTC1574 to
minimize system noise compared to
other devices that carry significantly
higher peak currents. This eases
shielding and filtering requirements
and decreases component stresses.
Output currents of up to 450mA are
possible with this device when the
I
PROGRAM
pin is connected to V
INPUT
,
increasing the peak current to 600mA.
The LTC1574 is available in fixed
5V, fixed 3.3V, and adjustable ver-
sions in the 16-lead narrow SOIC
package.
The LT1319 consists of a photo-
diode preamplifier followed by two
separate gain channels and compara-
tors. The preamplifier converts the
current from an external photodiode
to a voltage and has a transimpedance
gain internally set to 13kΩ. The band-
width of the preamp is 6MHz, which
allows reception of very high data
rates. The input-referred noise is a
low 2pAHz, which provides high
sensitivity and therefore greater trans-
mission distances. A highpass filter
loop within the preamp rejects ambi-
ent interference. The cutoff frequency
of this loop is easily adjustable with a
capacitor to ground. After further
external filtering, which can be tai-
lored to the desired communication
standards, two channels with high
input impedance and a gain of 400V/
V amplify the signal and drive com-
parators with adjustable thresholds.
One comparator has a response time
of 25ns and is well suited for data
rates up to 4MBaud or high-fre-
quency, carrier-based modulation
methods. The second comparator has
a 60ns response time and is useful for
more modest data rates such as in
the IrDA and Sharp/Newton stan-
dards. The gain stages also contain
highpass filter loops for further am-
bient rejection. A shutdown feature
reduces power from 14mA to 500µA.
LTC1574 High-Efficiency
Step-Down DC/DC Converter
with Internal Schottky Diode
The new LTC1574 requires only
three external components, an in-
ductor and two capacitors, to
construct a space saving, efficient
step-down DC/DC converter with
better than 90% efficiency. With its
internal low R
DS(ON)
switch (0.9Ω at a
supply voltage of 12V) and low for-
ward drop Schottky diode (0.390V at
200mA), external components are
minimized, leaving only the input
capacitor, output capacitor, and a
small surface-mount inductor. The
LTC1574 features a wide 4V-to-18.5V
LTC1177 Isolated,
High-Side Driver
The LTC1177 isolated high-side
driver is targeted at telecommunica-
tions, power supply, line-operated,
intrinsically safe, and RF-control ap-
plications. It provides isolated gate
drive for floating MOSFETs at volt-
ages up to 2.5kV. Among many
possible uses, it can drive a pair of
back-to-back MOSFET switches as a
fully isolated AC line relay. The
LTC1177 outperforms photoMOS re-
lays in most applications, since it can
drive large, low-resistance FETs with
far less input current.
To simplify designs, a current lim-
iter and active turn-off circuit are
included on chip. Input current to
operate the chip is 2.5mA, and stray
coupling from input to output is only
2pF, limiting leakage currents from
117V circuits to less than 100nA. The
LTC1177 is supplied in both DIP and
SO packages; samples are available
now.
The LT1319: A Low-Noise,
High-Speed Photodiode
Amplifier for Infrared Data
Transmission
The LT1319 is a general-purpose
infrared receiver that converts cur-
rent from a photodiode to a digital
signal. It is designed to easily provide
IR communications between portable
computers, personal digital assistants
(PDAs), desktop computers, and
peripherals such as printers.
The LT1319 supports low-speed
standards such as Infrared Data As-
sociation (IrDA) and Sharp/Newton,
as well as the emerging faster data
rate standards above 1MBaud.
Key features of the LT1319 include
a low-noise, high-speed preamplifier
for high data rates at long distances,
AC coupling loops that reject ambi-
ent interference, two gain channels
and two comparators to detect mul-
tiple standards, single 5V supply
operation, a power-saving shutdown
feature, and a 16-lead SOIC package.
For further information on the
above or any of the other devices
mentioned in this issue of Linear
Technology, use the reader service
card or call the LTC literature ser-
vice number: 1-800-4-LINEAR. Ask
for the pertinent data sheets and
application notes.