LTC6803-2 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC6803-2' PDF : 40 Pages View PDF
LTC6803-2/LTC6803-4
APPLICATIONS INFORMATION
V+
1
2 C12
S12
3
4 C11
S11
5
C10
6
7 S10
8 C9
9 S9
10 C8
11 S8
12 C7
13 S7
14 C6
S6
15
C5
16
17 S5
18 C4
19 S4
20 C3
21 S3
22 C2
23 S2
24 C1
S1
25
C0
26
ZCLAMP
ZCLAMP
ZCLAMP
LTC6803-4
ZCLAMP
ZCLAMP
ZCLAMP
A3 40
A2 39
A1 38
A0 37
VREG 32
VREF 31
VTEMP2
30
VTEMP1
29
CSBI 44
SDO 43
SDI 42
SCKI 41
GPIO2 36
GPIO1 35
WDTB
34
TOS
33
V–
27
NOTE: NOT SHOWN ARE PN DIODES TO ALL OTHER PINS FROM PIN 27
Figure 13. Internal Protection Diodes
680324 F13
For sensors that require higher drive currents, a buffer
op amp may be used as shown in Figure 15. Power for
the sensor is actually sourced indirectly from the VREG
pin in this case. Probe loads up to about 1mA maximum
are supported in this configuration. Since VREF is shut
down during the LTC6803 idle and shutdown modes, the
thermistor drive is also shut off and thus power dissipa-
tion minimized. Since VREG remains always on, the buffer
op amp (LT6000 shown) is selected for its ultralow power
consumption (12µA).
32
LTC6803-4
VREG
VREF
VTEMP2
VTEMP1
NC
V–
100k
100k
1µF
1µF
100k
100k
NTC
NTC
680324 F14
Figure 14. Driving Thermistors Directly from VREF
+
LT6000
–
LTC6803-4
VREG
VREF
VTEMP2
VTEMP1
NC
V–
10k
10k
10k
10k
NTC
NTC
680324 F15
Figure 15. Buffering VREF for Higher Current Sensors
Expanding Probe Count
As shown Figure 16, a dual 4:1 multiplexer is used to ex-
pand the general purpose VTEMP1 and VTEMP2 ADC inputs
to accept 8 different probe signals. The channel is selected
by setting the general purpose digital outputs GPIO1 and
GPIO2 and the resultant signals are buffered by sections
of the LT6004 micropower dual operational amplifier. The
probe excitation circuitry will vary with probe type and is
not shown here.
Another method of multiple sensor support is possible
without the use of any GPIO pins. If the sensors are PN
diodes and several used in parallel, then the hottest diode
will produce the lowest forward voltage and effectively
establish the input signal to the VTEMP input(s). The hottest
diode will therefore dominate the readout from the VTEMP
inputs that the diodes are connected to. In this scenario,
the specific location or distribution of heat is not known,
but such information may not be important in practice.
Figure 17 shows the basic concept. In any of the sensor
configurations shown, a full-scale cold readout would be
an indication of a failed-open sensor connection to the
LTC6803.
680324f
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