UNITRODE UC3704 Technical data

This integrated circuit contains a complete signal conditioning sys­tem to interface low-level variable impedance transducers to a
digital system. A pair of matched, temperature-compensated cur­rent sources are p rovided for balanced transducer excitation fol­lowed by a precision, high-gain comparator. The output of this
comparator can be delayed by a user-selectable duration, after
which a second comparator will switch complementary outputs
separately activated for diagnostic operation and has an optional
latch with external rese t capabil ity. An added feature is a high cur­rent power source useful as a heater driver in differential tempera­ture sensing applications. The UC3704 is designed for 0°C to
+70°C environments.

查询UC3704供应商

Bridge Transduc er Swit ch

UC3704

FEATURES

• Dual Matched Current Sources

• High-gain Differential Sensing Circuit

• Wide Common-mode Input Capability

• Complementary Digital Open-collector

Outputs

• Externally Programm a ble Time Delay

• Optional Output Latch with Reset

• Built-in Diagnostic Activation

• Wide Supply Voltage Range

• High Current Heater Power Source Driver

DESCRIPTI ON

UC3704 COMPATIBLE SE NSO RS

SENSOR TYPE ACTIVATION SOURCE

Temperature Pressure Force Position Displacement Velocity Shock
Thermistor X X
Sensistor X X
Thermocouple X
Semiconductor X X X
Photo Voltaic X X X
Photo Resistive X X X
Strain Gag e XXXXXX
Piezoelectric X X X X X
Magneto Resistive X X
Inductive XXXX
Hall Effect X X
Capacitive X

BLOCK DIAGRA M

6/93

UC3704

ABSOLUTE MAXI MUM RATING S

CONNECTION DIAGRAM

Supply Voltage ( +V IN). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 V

Output Current (each output) . . . . . . . . . . . . . . . . . . . . . . 50 mA

Buffer Power So urce Current. . . . . . . . . . . . . . . . . . . . . 200mA

Compara to r 1 Inputs. . . . . . . . . . . . . . . . . . . . . . . -0.5V to V

REF

DIL-16 (TOP VI EW)
J or N Package

Compara to r 2 Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to 5.5V

Remote Activa tion and Reset Inpu ts . . . . . . . . . . . . . . 0 to 5.5V

Power Dissipation at T

A = 25°C . . . . . . . . . . . . . . . . . . 1000mW

Operating Junct ion Te mp era tu re . . . . . . . . . . . -55°C to +150°C

Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C

Lead Tempera ture (Solder ing, 10 Seconds) . . . . . . . . . +3 00°C

Note: Unless otherw ise specified, all volta ges are with respect

to ground (Pin 1).
Currents are positiv e into , negat ive out of th e specified
terminal.
Consult Packag in g sect ion of Dat abo ok f or therm al
imitations and con sider at ions of package.

ELECTRICAL CHARACTERISTICS:

Unless otherwise state d, these spe cifica tion s apply for TA = 0°C to +70°C for the
UC3704: V

IH = 15V, TA =TJ.

PARAMETERS TEST CONDITION S MIN TYP MAX UNITS

Power Inputs

Supply Voltage Range 4.2 36 V
Supply Current V

Reference Sec tion ( w ith respect to V

REF Value |VIN - VREF|TJ = 25°C 2.1 2.2 2.3 V

V
V

REF Temperatur e Coeff icie nt Note 1 -1 -2 -3 mV/°C

IN)

Line Regulatio n ∆V
Load Regulation ∆I
Short Circuit Current V

IN = 36V 5 10 mA

IN = 4.2 to 25V 2 10 mV

O = 0 to 4mA 2 10 mV

IN = 36V, VREF = VIN or Ground

±

25 mA

Current Source ( Q1 and Q 2)

Output Cur rent (Note 2) Current Set = 10µA-9-9.5-10µA

Current Set = 200 µA -180 -195 -200 µA

Output Offset Current R

E6 = RE8 = 20kΩ 0

±

1 µA

Comparator One

Input Offs et Vo lta ge

±

±

1

4mV
Input Bias Cur rent -100 -300 nA
Input Offs et Cu rr ent
CMRR V
Voltage gain R

CM = 0 to 12V 60 70 dB
L>150kΩ 70 85 dB

±

60 nA

Delay Current Source 34 40 52 µA
Output Rise Time Overdrive = 10mV, C

D = 15pF, TJ = 20° C 2 V/µs

2

UC3704

ELECTRICAL CHARACTERIST ICS :

PARAMETER TEST CONDITIONS M IN TYP MAX UNITS

Comparator Two (Q

Threshold Voltage 2.2 3.0 3.8 V
Threshold Resistanc e To Ground 14 20 24 kΩ
Input Bias Cur rent V
Remote Activat e Cur ren t Pin 14 = 0V 0.2 0.5 mA
Reset Current Pin 13 = 0V 0.2 0.5 mA
Remote Activat e Thr esh old T
Reset Threshold T
Output Saturation I

Output Lea kage V
Output Resp onse Comp. O verdrive = 1V

Buffer

Set Voltage (V
Drive Current T

OUT

and QOUT)

IN -VS)TJ = 25°C, IS = 100mA 1.9 2.1 2.3 V

Unless otherw ise stat ed, these sp ecif icat io ns apply for TA = 0°C to +70°C for the
UC3704: V

IN (Pin 12) = 5V 1 3 µA

A = 25°C 0.8 1.2 V

A = 25°C 0.8 1.2 V
OUT = 16mA 0.2 0.5 V
OUT = 50mA 0.7 2.0 V

I

OUT = 40V 0.2 10 µA

R

L

J = 25°C, RS = 200Ω, VD = 0V 90 100 120 mA

IH = 15V, TA =TJ.

= 5k to VIN

Turn- on 0.4 µs
Turn- of f 1.0 µs

Note 1: Parameter guar anteed by design, not tested in productio n.

IN

−

V

REF

−

V

Note 2: Collector out put cur re nt =

V

BE

R

E

≈

1.5

R

V

E

APPLICATIONS INFORMATION

Sensor Section

The input portion of the UC3704 provides both excitation
and sensing for a low-level, variable impedance
transducer. This circuitry consists of a pair of highly
matched PNP transistor s biased for operation as constant
current sources followed by a hi gh gain precision compa­rator.

The reference voltage at the bases of the PNP transistors
has a TC to offset the base-emitter voltage variation of
these transistors resulting in a constant voltage across
the external emitter resistors and correspondingly con­stant collector currents for balancing, offsetting, or to pro­vide unique temperature characterist ic.

With the PNP transistor’s optimum current ranging from
10 to 200µA, and the common-mode input voltage of the
comparator usable from ground to (V
range of transducer impedance levels is possible.

The sensor comparator has a current source pull-up at
the output so that an external capacitor from this point to

IN - 3V), a wide

ground can be used to provide a programmable delay be­fore reaching the second comparator’s threshold. The
low-impedance on-state of Comp 1’s output provides
quick reset of this capacitor. This programmable delay
function is useful for providing transi ent protection by re­quiring that Comp 1 remain activated for a finite period of
time before Comp 2 triggers. Another application is in
counting repe titive pulses where a missing pulse will al­low Comp 1’s output to rise to Comp 2’s threshold. This
time delay function is:

Delay

=

Delay

Threshold

Current

X

C

D

≈ 175

ms

⁄

µ

F

Comp

2

If hysteresis is desired for Comparator 1, it may be ac­commodated by applyin g positive feedback from the de­lay ter minal to the n on-inverting i nput on Pin 7. This will
aid in provid ing oscillation-free transitions for very slowly
changing inputs.

3

APPLICATIONS INFORMATION (cont.)

Output Section

The output portion of the UC3704 is basically a second
comparator with complimentary, open-collector outputs.
This comparator has a built-in, ground-referenced thresh­old implemented with a high-impedance current source
and resistor so that it may be easil y overridden with an
external voltage source if desired. Comp 2’s input tran­sistors are NPN types which require at least 1V of com­mon-mode voltage for accurate operation and should not
see a differentia l input voltage greater than 6V.

For diagnostic or latching purposes, the output logic is
equipped with a Remote Activate and Reset function.
These pins have internal pull-ups and are only active
when pulled low below a threshold of approximately 1V . A
low signal at the Remote Activate Pin causes the outputs
to change state in exactly the same manner as if Comp
2’s input is raised above the threshold on Pin 11. If Pin
16 is connected to Pi n 14, positive feedback results and
the outputs will latch once triggered by Comp 2’s input.

UC3704

Pulling the Reset terminal low overrides the Remote Acti­vate Pin releasing the latch.

Reference Buffer

This circuit is designed to provide up to 100mA to drive a
high current external PNP transistor useful for powering
a heater for differential temperature measurements. Care
must be taken that power dissipation in Q6 does not
cause excessive thermal gradients which will degrade
the accuracy of the sensing circuitry.

Using a heating element a ttached to a temperature sen­sitive resis tor, RS1, in one leg o f the inp ut bridge i mple­ments a flow sensor for either gasses or liquids. As long
as there is flow, heat from the element is carried away
and the sensor vol tage remains below threshol d. Using
an identical sensor, RS2, without a heater to establish
this threshold compensates for the ambie nt temperature
of the flow.

TYPICAL APPL ICATION FOR MONITORING LIQUID OR GAS FLOW

UNITRODE INTEGRATED CIRCUITS
7 CONTINENTAL BLVD.•• MERRIMACK, NH 03054
TEL. [phone] •• FAX [phone]

4

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