Datasheet

Rev 03 Jan 2013 19:42 | Page 7
Additional Low-Pass Filters
The components R14, C13, R19 and C15 offer additional filtering options. The pin labeled VFILT is
located after the first filter (R14 and C13). The pin labeled VFILT2 is located after both filters.
LEADS-OFF DETECTION
The AD8232 includes leads off detection features. It provides modes optimized for either two or
three-electrode configurations.
DC Leads-Off Detection
To use this mode, the switch position must match the text labeled as “DC” on the silkscreen. This
mode works by sensing when either input goes high. Note that the system must be a three-electrode
configuration to operate properly. Therefore, the RLD output terminal must be connected to a driven
electrode.
In DC leads-off mode, the AD8232 checks each input individually, and is therefore able to indicate
which electrode is disconnected. The AD8232 indicates which electrode is disconnected by setting the
corresponding LO- or LO+ pin high.
AC Leads-Off Detection
To use this mode, the switch position must match the text labeled as “AC” on the silkscreen. To
maintain the inputs inside the common-mode range of the amplifier, provide a bias return path for
each input with a 10MΩ to REFOUT (through J1) or PRLD (through J3).
This mode is useful when using only two electrodes (no separate driven electrode). The AD8232
detects when an electrode is disconnected by sourcing a small 100 kHz current into the electrodes. As
opposed to the DC detection mode, the ADC8232 is only able to determine that an electrode has lost
its connection – not which one. During such event, the LO+ pin goes high. In this mode, the LO- pin is
not used.
FAST RESTORE
The fast restore function (FR) reduces the duration of otherwise long settling tails of the high-pass
filters. After an abrupt change that rails the amplifier (such as a leads-off condition), the AD8232
automatically adjusts to higher filter cutoff. This functionality allows the AD8232 to recover quickly,