Datasheet

INA330
7
SBOS260
www.ti.com
loop can be accomplished by simply reversing the connec-
tions to the TEC, or by creating the desired polarity in the
intervening control circuitry. If differing values of V
1
and V
2
are used, resistor values should be chosen to maintain
balanced currents, I
1
and I
2
. Likewise, if a lower value of R
SET
is used, the excitation voltage must be lowered to keep I
1
and
I
2
at or below 125µA.
C
FILTER
is calculated by:
C
R kHz
FILTER
G
=
(
)
1
216π .
NOISE PERFORMANCE
Temperature control loops require low noise over a small
bandwidth, typically 10Hz, or less. The INA330’s internal
auto-correction circuitry eliminates virtually all 1/f noise (noise
that increases at low frequency). The peak-to-peak voltage
noise due to I
ERROR
, R
THERM
, R
SET
, and the buffers at 0.01Hz
to 10Hz results in a 0.0001°C contribution.
OUTPUT
The INA330 output (pin 8) is capable of swinging to within
10mV of the power-supply rails. It is able to achieve rail-to-
rail output performance while sinking or sourcing 12.5µA.
V
ADJUST
can be used to create an offset voltage around which
the output can be centered.
ENABLE FUNCTION
The INA330 is enabled by applying a logic HIGH voltage
level to the Enable pin. Conversely, a logic LOW voltage
level will disable the amplifier, reducing its supply current
from 2.6mA to typically 2µA. This pin should be connected to
a valid HIGH or LOW voltage or driven, not left open circuit.
Applications not requiring disable can connect pin 6 directly
to V+. The Enable pin can be modeled as a CMOS input
gate, as shown in Figure 4.
SELECTING COMPONENTS
R
SET
is the primary “reference” for the temperature control
loop. Its absolute resistance controls the set-point tempera-
ture. Again, its initial accuracy can be calibrated, but its
stability is crucial. Therefore, a high-quality, low-temperature
coefficient type must be used.
A 25ppm/°C precision resistor changes 0.15% from –40°C to
+85°C. This will produce a 0.03°C change in set-point tem-
perature. This error is approximately three-times larger than
that produced by the INA330.
The transfer function for the configuration shown in Figure 3 is:
VV RII
O
ADJ
G
=+
( )
12
–
or
VV R
V
R
V
R
O
ADJ
G
THERM
SET
=+






12
–
With V
1
= V
2
= V
EXCITE
,
VV V R
RR
O
ADJ
EXCITE G
THERM
SET
=+






11
–
2
3
10
1
95
4
V+
V
2
V
EXCITE
1V
V
1
6
Enable High = On
Low = Off
8
7
I
1
I
2
R
SET
10kΩ
R
G
200kΩ
Thermistor
R
THERM
= 10kΩ
C
FILTER
500pF
I
O
= I
1
– I
2
V
O
V
ADJUST
= +2.5V
FIGURE 3. Basic Configuration for the INA330.
V+
Enable
6
2µA
FIGURE 4. Enable Pin Model.
Nominal values should use R
SET
= R
THERM
= 10kΩ at the
designed control temperature. Values less than 2kΩ can
cause the voltage excitation buffers to become unstable. The
buffer connected to pin 10 is characterized and tested to
supply the changing current in the thermistor. The thermistor
should not be connected to pin 1. An inversion of the control