Datasheet

51kW
51kW
100kW
100kW
47nF
51kW
100kW
47nF
47nF
4-Bit
DAC
Skin,
ElectrodeContact
Model
Patient
Protection
Resistor
AVDD
LOFF_SENSP
VLEAD_OFF_EN
AND
AVSS
LOFF_SENSN
VLEAD_OFF_EN
AND
LOFF_SENSP
VLEAD_OFF_EN
AND LOFF_SENSN
VLEAD_OFF_EN
AND
RLDOUT
FLEAD_OFF[1:0]
Vx
3.3MW
3.3MW
3.3MW
3.3MW
3.3MW
3.3MW
AntialiasingFilter
<512kHz
FLEAD_OFF[0:1]
AVDD AVSS
ToADC
LOFF_STATP
LOFF_STATN
COMP_TH[2:0]
V
INP
V
INN
(AVDD+AVSS)/2
7MW 7MW
10pF 10pF
PGA
EMI
Filter
12pF
12pF
Patient
ADS1194, ADS1196
ADS1198
www.ti.com SBAS471C –APRIL 2010– REVISED NOVEMBER 2011
LEAD-OFF DETECTION
Patient electrode impedances are known to decay over time. It is necessary to continuously monitor these
electrode connections to verify a suitable connection is present. The ADS1194/6/8 lead-off detection functional
block provides significant flexibility to the user to choose from various lead-off detection strategies. Though called
lead-off detection, this is in fact an electrode-off detection.
The basic principle is to inject an excitation signal and measure the response to find out if the electrode is off. As
shown in the lead-off detection functional block diagram in Figure 46, this circuit provides two different methods
of determining the state of the patient electrode. The methods differ in the frequency content of the excitation
signal. Lead-off can be selectively done on a per channel basis using the LOFF_SENSP and LOFF_SENSN
registers. Also, the internal excitation circuitry can be disabled and just the sensing circuitry can be enabled.
Figure 46. Lead-Off Detection
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