SC1200 datasheet(17/60 Pages) TI

17 / 60 page

MSC1200

SBAS289E

www.ti.com

FIGURE 6. Input Multiplexer Configuration.

FIGURE 7. Analog Input Structure (without buffer).

INPUT MULTIPLEXER

The input multiplexer provides for any combination of differential

inputs to be selected as the input channel, as shown in Figure 6.

If AIN0 is selected as the positive differential input channel, any

other channel can be selected as the negative differential input

channel. With this method, it is possible to have up to eight fully

differential input channels. It is also possible to switch the polarity

of the differential input pair to negate any offset voltages.

In addition, current sources are supplied that will source or

sink current to detect open or short circuits on the pins.

TEMPERATURE SENSOR

On-chip diodes provide temperature sensing capability. When

the configuration register for the input MUX is set to all 1s,

the diodes are connected to the input of the ADC. All other

channels are open.

BURNOUT DETECT

When the Burnout Detect (BOD) bit is set in the ADC control

configuration register (ADCON0 DCH), two current sources are

enabled. The current source on the positive input channel sources

approximately 2

µA of current. The current source on the negative

input channel sinks approximately 2

µA. This allows for the

detection of an open circuit (full-scale reading) or short circuit

(small differential reading) on the selected input differential pair.

Enabling the buffer is recommended when BOD is enabled.

INPUT BUFFER

The analog input impedance is always high, regardless of

PGA setting (when the buffer is enabled). With the buffer

enabled, the input voltage range is reduced and the analog

power-supply current is higher. If the limitation of input

voltage range is acceptable, then the buffer is always pre-

ferred.

The input impedance of the MSC1200 without the buffer

is 7M

Ω/PGA. The buffer is controlled by the state of the BUF

bit in the ADC control register (ADCON0 DCH).

ANALOG INPUT

When the buffer is not selected, the input impedance of the

analog input changes with ACLK clock frequency (ACLK

F6H) and gain (PGA). The relationship is:

pedance

MHz

ACLK Frequency

PGA

IN Im

( )

Ω=









•

Ω









where ACLK frequency (fACLK) =

ACLK

CLK

+ 1

and fMOD =

ACLK

Figure 7 shows the basic input structure of the MSC1200.

SWITCH

(3k

Ω typical)

Sampling Frequency = f

SAMP

High Impedance

> 1G

Ω

AGND

PGA

SAMP

1, 2, 4

MOD

× f

MOD

× f

MOD

× f

MOD

64, 128

× f

MOD

PGA

9pF

18pF

4 to 128

36pF

AIN3

AIN4

AIN5

AIN6

AIN0

AIN1

AIN2

AIN7

AINCOM

Burnout Detect (2

µA)

Burnout Detect (2

µA)

AGND

Buffer

Temperature Sensor

80 • I

In+

In–

SC1200 Datasheet(PDF) 17 Page - Texas Instruments

SC1200 Datasheet(HTML) 17 Page - Texas Instruments

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