ASD1194 datasheet(56/76 Pages) TI

56 / 76 page

a)LOFF_FLIP=0

a)LOFF_FLIP=1

PGA

10M

AVDD

INP

INN

PGA

10M

AVDD

INP

INN

ADS119x

a)Pull-Up/Pull-DownResistors

b)CurrentSource

PGA

10M

AVDD

INP

INN

PGA

AVDD

INP

INN

ADS119x

ADS1194, ADS1196

ADS1198

SBAS471C

– APRIL 2010 – REVISED NOVEMBER 2011

www.ti.com

DC Lead-Off

In this method, the lead-off excitation is with a dc signal. The dc excitation signal can be chosen from either a

pull-up/pull-down resistor or a current source/sink, shown in Figure 47. The selection is done by setting the

VLEAD_OFF_EN bit in the LOFF register. One side of the channel is pulled to supply and the other side is pulled

to ground. The pull-up resistor and pull-down resistor can be swapped (as shown in Figure 48) by setting the bits

in the LOFF_FLIP register. In case of current source/sink, the magnitude of the current can be set by using the

ILEAD_OFF[1:0] bits in the LOFF register. The current source/sink gives larger input impedance compared to the

10M

Ω pull-up/pull-down resistor.

Figure 47. DC Lead-Off Excitation Options

Figure 48. LOFF_FLIP Usage

Sensing of the response can be done either by looking at the digital output code from the device or by monitoring

the input voltages with an on-chip comparator. If either of the electrodes is off, the pull-up resistors and/or the

pull-down resistors saturate the channel. By looking at the output code it can be determined that either the P-side

or the N-side is off. To pinpoint which one is off, the comparators must be used. The input voltage is also

monitored using a comparator and a 4-bit DAC whose levels are set by the COMP_TH[2:0] bits in the LOFF

registers are available as a part of the output data stream. (See the Data Output (DOUT) subsection of the SPI

Interface section.) If dc lead-off is not used, the lead-off comparators can be powered down by setting the

PD_LOFF_COMP bit in the CONFIG4 register.

An example procedure to turn on dc lead-off is given in the Lead-Off subsection of the Quick-Start Guide section.

Submit Documentation Feedback

Product Folder Link(s): ADS1194 ADS1196 ADS1198

ASD1194 Datasheet(PDF) 56 Page - Texas Instruments

ASD1194 Datasheet(HTML) 56 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

Datasheet Download

Link URL