Datasheet

 2015-2017 Microchip Technology Inc. DS20005426C-page 39
MCP9600
6.3 Device Features
6.3.1 I
2
C ADDRESSING
The MCP9600 supports up to eight devices on the I
2
C
bus. Applications, such as large thermal management
racks with several thermocouple sensor interfaces, are
able to monitor various temperature zones with minimal
pin count microcontrollers. This reduces the total solu-
tion cost, while providing a highly accurate thermal
management solution using the MCP9600.
FIGURE 6-4: I
2
C Address Selection
Implementation.
6.3.2 INPUT IMPEDANCE
The MCP9600 uses a switched capacitor amplifier input
stage to gain the input signal to a maximum resolution of
2 µV/LSb at an 18-bit ADC setting. An internal input
capacitor is used for charge storage. The differential
input impedance, Z
IN_DF
, is dominated by the sampling
capacitor and the switched capacitor amplifier sampling
frequency. During a sampling period, the charging and
discharging of the sampling capacitor creates dynamic
input currents at the input pins. Adding a 10-100 nF
capacitor between the inputs can improve stability.
Since the sampling capacitor is only switching to the
input pins during a conversion process, the input
impedance is only valid during conversion periods.
During Low-Power or Shutdown mode, the input ampli-
fier stage is disabled; therefore, the input impedance is
Z
IN_CM
, which is due to the leakage current from ESD
protection diodes, as shown in Figure 6-5.
FIGURE 6-5: Thermocouple Input Stage.
6.3.3 OPEN AND SHORT DETECTION
CIRCUITS
External circuits can be added to detect the thermo-
couple status as open (physically disconnected) or as
short (thermocouple wire in contact with the system
ground or V
DD
). If a passive circuit is added to the input
stage, then the circuit loading effect to the MCP9600
ADC inputs must be considered. System calibration is
also required to ensure proper accuracy. In addition,
external loads can degrade the device performance,
such as input offset, gain and Integral Nonlinearity
(INL) errors. If a low-impedance active circuit is added,
then both offset and gain errors must be calibrated.
MCP9600
PIC
®
I
2
C
Alert
4
GND
Typ es K , J, T, N ,
E, B, S, R
V
DD
Alert
4
GND
V
DD
MCP9600
R
7A
R
7B
R
2A
R
2B
TABLE 6-2: RECOMMENDED
RESISTOR VALUES FOR
I
2
C ADDRESSING
Device #
Command
Byte
Values
R
XA
(k)R
XB
(k)
1 1100 000x ADDR Pin Tied to GND
2 1100 001x R
2A
= 10 R
2B
= 2.2
3 1100 010x R
3A
= 10 R
3B
= 4.3
4 1100 011x R
4A
= 10 R
4B
= 7.5
5 1100 100x R
5A
= 10 R
5B
= 13
6 1100 101x R
6A
= 10 R
6B
= 22
7 1100 110x R
7A
= 10 R
7B
= 43
8 1100 111x ADDR Pin Tied to V
DD
Note: Standard 5% tolerance resistors are used in
the table; however, 1% tolerance resistors
provide better ratio matching.
ADDR
ADDR
V
IN+
V
IN-
V
IN+
V
IN-
Microcontroller
Unit 2/8
Unit 7/8
Up to Eight
MCP9600 Devices
on I
2
C Bus
Ty pe s K , J , T, N,
E, B, S, R
R
SS
V
IN
+,V
IN
-
Sampling
Switch
SS
R
S
C
SAMPLE
(3.2 pF)
V