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PDF LTC1041 Data sheet ( Hoja de datos )
| Número de pieza | LTC1041 | |
| Descripción | BANG-BANG Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Micropower 1.5µW (1 Sample/Second)
s Wide Supply Range 2.8V to 16V
s High Accuracy
Guaranteed SET POINT Error ±0.5mV Max
Guaranteed Deadband ±0.1% of Value Max
s Wide Input Voltage Range V+ to Ground
s TTL Outputs with 5V Supply
s Two Independent Ground-Referred Control Inputs
s Small Size 8-Pin SO
U
APPLICATIO S
s Temperature Control (Thermostats)
s Motor Speed Control
s Battery Charger
s Any ON-OFF Control Loop
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation.
LTC1041
BANG-BANG Controller
DESCRIPTIO
The LTC®1041 is a monolithic CMOS BANG-BANG
controller manufactured using Linear Technology’s
enhanced LTCMOS™ silicon gate process. BANG-BANG
loops are characterized by turning the control element
fully ON or fully OFF to regulate the average value of
the parameter to be controlled. The SET POINT input
determines the average control value and the DELTA input
sets the deadband. The deadband is always 2 x DELTA and
is centered around the SET POINT. Independent control
of the SET POINT and deadband, with no interaction, is
made possible by the unique sampling input structure of
the LTC1041.
An external RC connected to the OSC pin sets the sampling
rate. At the start of each sample, internal power to the
analog section is switched on for ≈ 80µs. During this time,
the analog inputs are sampled and compared. After the
comparison is complete, power is switched off. This
achieves extremely low average power consumption
at low sampling rates. CMOS logic holds the output
continuously while consuming virtually no power.
To keep system power at an absolute minimum, a switched
power output (VP-P) is provided. External loads, such as
bridge networks and resistive dividers, can be driven by
this switched output.
The output logic sense (i.e., ON = V+) can be reversed
(i.e., ON = GND) by interchanging the VIN and SET POINT
inputs. This has no other effect on the operation of
the LTC1041.
TYPICAL APPLICATIO
Ultralow Power 50°F to 100°F (2.4µW) Thermostat
26V AC 2-WIRE THERMOSTAT
0.1µF
56Ω
2N6660
1N4002
(4)
†
4.32k
5k
6.81k
49.9Ω
4.99k
1
2
3
4
LTC1041
8
7
6
5
DELTA = 0.5°F
10M IS
400nA
+
1µF
6V
ALL RESISTORS 1%. † YELLOW SPRINGS INSTRUMENT CO., INC. P/N 44007. LTC1041 • TA01
DRIVING THERMISTOR WITH VP-P ELIMINATES 3.8°F ERROR DUE TO SELF-HEATING
Supply Current vs Sampling Frequency
10000
VS = 6V
1000
100
TOTAL SUPPLY
CURRENT
10
1
LTC1041 SUPPLY
CURRENT
0.1
0.01
0.1
1 10 100 1000 10000
SAMPLING FREQUENCY, fS (Hz) LTC1041 • TA02
1041fa
1
1 page  
LTC1041
APPLICATIO S I FOR ATIO
RS
S1
+
CIN
(≈ 33pF)
VIN CS
S2
–
V–
LTC1041 DIFFERENTIAL INPUT
LTC1041 • AI01
Figure 2. Equivalent Input Circuit
RS • CIN. The ability to fully charge CIN from the signal
source during the controller’s active time is critical in
determining errors caused by the input charging current.
For source resistances less than 10kΩ, CIN fully charges
and no error is caused by the charging current.
For RS > 10kΩ
For source resistances greater than 10kΩ, CIN cannot fully
charge, causing voltage errors. To minimize these errors,
an input bypass capacitor, CS, should be used. Charge is
shared between CIN and CS, causing a small voltage error.
The magnitude of this error is AV = VIN • CIN (CIN + CS). This
error can be made arbitrarily small by increasing CS.
The averaging effect of the bypass capacitor, CS, causes
another error term. Each time the input switches cycle
between the plus and minus inputs, CIN is charged and
discharged. The average input current due to this is
IAVG = VIN • CIN • fS, where fS is the sampling frequency.
Because the input current is directly proportional to the
differential input voltage, the LTC1041 can be said to have
an average input resistance of RIN = VIN/IAVG = I/(fS • CIN).
Since two comparator inputs are connected in parallel, RIN
is one half of this value (see typical curve of RIN versus
Sampling Frequency). This finite input resistance causes
an error due to the voltage divider between RS and RIN.
The input voltage error caused by both of these effects is
VERROR = VIN [2CIN/(2CIN + CS) + RS/(RS + RIN)].
Example: assume fS = 10Hz, RS = 1M, CS = 1µF, VIN = 1V,
VERROR = 1V(66µV + 660µV) = 726µV. Notice that most of
the error is caused by RIN. If the sampling frequency is
reduced to 1Hz, the voltage error from the input
impedance effects is reduced to 136µV.
Input Voltage Range
The input switches of the LTC1041 are capable of
switching either to the V+ supply or ground. Consequently,
the input voltage range includes both supply rails. This is
a further benefit of the sampling input structure.
Error Specifications
The only measurable errors on the LTC1041 are the
deviations from “ideal” of the upper and lower switching
levels (Figure 1b). From a control standpoint, the error in
the SET POINT and deadband is critical. These errors may
be defined in terms of VU and VL.
SET POINT error
≡
VU
+
2
VL
– SET POINT
deadband error ≡ (VU – VL ) – 2 • DELTA
The specified error limits (see electrical characteristics)
include error due to offset, power supply variation, gain,
time and temperature.
Pulsed Power (VP-P) Output
It is often desirable to use the LTC1041 with resistive
networks such as bridges and voltage dividers. The power
consumed by these resistive networks can far exceed that
of the LTC1041 itself.
At low sample rates the LTC1041 spends most of its time
off. A switched power output, VP-P, is provided to drive the
input network, reducing its average power as well. VP-P is
switched to V+ during the controller’s active time (≈ 80µs)
and to a high impedance (open circuit) when internal
power is switched off.
Figure 3 shows the VP-P output circuit. The VP-P output
voltage is not precisely controlled when driving a load
(see typical curve of VP-P Output Voltage vs Load Current).
In spite of this, high precision can be achieved in two ways:
(1) driving ratiometric networks and (2) driving fast set-
tling references.
In ratiometric networks all the inputs are proportional to
VP-P (Figure 4). Consequently, the absolute value of VP-P
does not affect accuracy.
1041fa
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1041.PDF ] | |
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