Datasheet

GPIO3
GPIO4
GPIO2
t
BLKDLY
(DemodulationClock)
(Blocki gn Si n l)g a
t
PHASE
(ModulationCl ck)o
Respiration
Modulation
Generator
RESP_PH[2:0]
CLK
(2.048MHz)
ModulationClock
DemodulationClock
GPIO4
GPIO3
GPIO2
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
www.ti.com SBAS459I –JANUARY 2010–REVISED JANUARY 2012
External Respiration Circuitry Option (RESP_CTRL = 01b)
In this mode, GPIO2, GPIO3, and GPIO4 are automatically configured as outputs. The phase relationship
between the signals is shown in Figure 65. GPIO2 is the exclusive-OR of GPIO3 and GPIO4, as shown in
Figure 66. GPIO3 is the modulation signal, and GPIO4 is the de-modulation signal. While in this mode, the
general-purpose pin function of GPIO2, GPIO3, and GPIO4 is not available. The modulation frequency can be
64kHz or 32kHz using RESP_FREQ[2:0] bits in the CONFIG4 register. The remaining bit options of
RESP_FREQ[2:0] generate square waves on GPIO3 and GPIO4. The exclusive-OR out on GPIO2 is only
available on 64kHz and 32kHz modes. The phase of GPIO4, relative to GPIO3, is set by RESP_PH[2:0] bits in
the RESP register.
The mode can be used when the user implements custom respiration impedance circuitry external to the
ADS129x.
Figure 65. External Respiration (RESP_CTRL = 01b) Timing Diagram
Table 15. Timing Characteristics for Figure 65
(1)
2.7V ≤ DVDD ≤ 3.6V 1.65V ≤ DVDD ≤ 2V
PARAMET
ER DESCRIPTION MIN TYP MAX MIN TYP MAX UNIT
Respiration phase delay, set by
t
PHASE
22.5 157.5 22.5 157.5 Degrees
RESP.RESP_PH[2:0] bits
Modulation clock rising edge to XOR
t
BLKDLY
1 5 ns
signal
(1) Specifications apply from –40°C to +85°C.
Figure 66. External Respiration (RESP_CTRL = 01b) Block Diagram
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Product Folder Link(s): ADS1294 ADS1294R ADS1296 ADS1296R ADS1298 ADS1298R