10
LTC1040
1040fa
TYPICAL APPLICATIO S
U
Figure 10. The LTC1040 as a Linear Amplifier
V
IN
V
OUT
LTC1040 • TA07
V
+
–
–
+
+
1/2 LTC1040
C
R
V
+
0V
t
ON
LTC1040 • TA08
t
OFF
V
OUT
= V
+
t
ON
t
ON
+
t
OFF
The LTC1040 as a Linear Amplifier
With a simple RC filter, the LTC1040 can be made to
function as a linear amplifier. By filtering the logic output
and feeding it back to the negative input, the loop forces
the output duty cycle [t
ON
/(t
ON
+ t
OFF
)] so that V
OUT
equals
V
IN
(Figure 10).
The RC time constant is set to keep the ripple on the output
small. The maximum output ripple is: ∆V = V
+
/f
S
RC and
should be set to 0.5mV to 1mV for best results. Notice that
the higher the sampling frequency, f
S
, the lower RC can be.
This is important because the RC filter also sets the loop
response. A convenient way to keep f
S
as high as possible
under all conditions is to connect a 100k resistor to pin 16
(OSC) with no capacitance to ground.
2-Wire 0°C to 100°C Temperature Transducer with 4mA to 20mA Output
LTC1040 • TA09
6
5
7
8
10
9
18
4
1M
16
††
+
+
–
–
1/2
LTC1040
†
6
4
1k
ZERO
ADJUST
100k
3200
18k
LT1019-5
6250
YELLOW SPRINGS INSTRUMENT
PART NO. 44201
1µF
10µF
FULL-SCALE
ADJUST
ACCURACY = + = ±0.3°C±0.1°C
CIRCUIT ERROR
AT 25°C
±0.2°C
TRANSDUCER
ERROR
5k 182Ω
50Ω
2N6657
1N914
LM134
430Ω
43
R
12V TO 40V
0°C = 4mA
100°C = 20mA
V
+
V
–
RETURN
+
+
