Datasheet

INA330
11
SBOS260
www.ti.com
FIGURE 10. Digitally Compensated Loop.
FIGURE 11. Traditional Bridge Circuit.
DIGITALLY COMPENSATED LOOP
The PID compensation can be replaced with a microcontroller
or DSP, as shown in Figure 10. An Analog-to-Digital (A/D)
converter would be used to digitize the output of the INA330.
The analog PID provides sufficient filtering inherently, and,
therefore requires no additional filtering. The digital control
loop shown in Figure 10 does not provide this inherent
filtering, requiring additional output filtering (R
O
and C
O
) as
shown to avoid sampling the internal chopping noise of the
INA330 and the A/D converter input and affecting accuracy.
High-frequency noise is created by internal auto-correction
circuitry and is highly dependent on the filter characteristics
chosen. “Spurs” occur at approximately 90kHz and its har-
monics which is reduced by additional filtering at or below
1kHz. This may be the dominant source of noise visible when
viewing the output on an oscilloscope. Low cutoff frequency
filters will provide lowest noise.
TRADITIONAL BRIDGE CIRCUIT
The traditional bridge circuit (Figure 11) uses three matched
resistors and a thermistor to detect temperature changes.
The INA326 and INA327 instrumentation amplifiers are well
suited to a bridge implementation for thermistor measure-
ment.
INA330
DSP
Loop Compensation
is performed in DSP.
TEC
+5V
Enable
+5V
R
SET
10kΩ
R
G
200kΩ
R
THERM
C
FILTER
500pF
V
ADJ
0V to 5V
D/A
Converter
Temp
Adjust
Ref
R
O
100Ω
C
O
1µF
A/D
Converter
D/A
Converter
+1V
V
2
V
1
3
2
95 6
8
7
5kΩ
10kΩ
(2)
10kΩ
(1)
10kΩ
(1)
✻ 10kΩ at set-point
temperature.
✻
NOTES: (1) Requires ratio matching tracking.
(2) Requires absolute accuracy and stability.
V
EXCITE
PID CONTROLLER
INA326
+5V
100kΩ
V
REF
2.5V
1nF
V
ADJ
D/A
Converter