Linear Technology LTC6804-1 - Page 22

LTC6804-1/LTC6804-2
22
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Table 2. isoSPI Supply Current Equations
isoSPI STATE DEVICE
ISOMD
CONNECTION I
REG(isoSPI)
IDLE LTC6804-1/LTC6804-2 N/A 0mA
READY LTC6804-1 V
REG
2.8mA + 5 • I
B
Note: I
B
=V
BIAS
/(R
B1
+R
B2
)
V
–
1.6mA + 3 • I
B
LTC6804-2 V
REG
1.8mA + 3 • I
B
V
–
0mA
ACTIVE LTC6804-1 V
REG
Write: 2.8mA + 5•I
B
+ 2•I
B
+ 0.4mA
( )
•
1µs
t
CLK
Read: 2.8mA + 5•I
B
+ 3•I
B
+ 0.5mA
( )
•
1µs
t
CLK
V
–
1.6mA+ 3 •I
B
+ 2•I
B
+ 0.2mA
( )
•
1µs
t
CLK
LTC6804-2 V
REG
Write: 1.8mA + 3 •I
B
+ 0.3mA
( )
•
1µs
t
CLK
Read: 1.8mA+ 3•I
B
+ I
B
+ 0.3mA
( )
•
1µs
t
CLK
V
–
0mA
operaTion
Mode 7kHz (Normal):
In this mode, the ADC has high resolution and low TME
(total measurement error). This is considered the normal
operating mode because of the optimum combination of
speed and accuracy.
Mode 27kHz (Fast):
In this mode, the ADC has maximum throughput but has
some increase in TME (total measurement error). So this
mode is also referred to as the fast mode. The increase
in speed comes from a reduction in the oversampling
ratio. This results in an increase in noise and average
measurement error.
Mode 26Hz (Filtered):
In this mode, the ADC digital filter –3dB frequency is
lowered to 26Hz by increasing the OSR. This mode is
also referred to as the filtered mode due to its low –3dB
frequency. The accuracy is similar to the 7kHz (Normal)
mode with lower noise.
Modes 14kHz, 3kHz and 2kHz:
Modes 14kHz, 3kHz and 2kHz provide additional options to
set the ADC digital filter –3dB frequency at 13.5kHz, 3.4kHz
and 1.7kHz respectively. The accuracy of the 14kHz mode
is similar to the 27kHz (fast) mode. The accuracy of 3kHz
and 2kHz modes is similar to the 7kHz (normal) mode.
Table 3. ADC Filter Bandwidth and Accuracy
MODE –3dB FILTER BW –40dB FILTER BW TME SPEC AT 3.3V, 25°C TME SPEC AT 3.3V,–40°C, 125°C
27kHz (Fast Mode) 27kHz 84kHz ±4.7mV ±4.7mV
14kHz 13.5kHz 42kHz ±4.7mV ±4.7mV
7kHz (Normal Mode) 6.8kHz 21kHz ±1.2mV ±2.2mV
3kHz 3.4kHz 10.5kHz ±1.2mV ±2.2mV
2kHz 1.7kHz 5.3kHz ±1.2mV ±2.2mV
26Hz (Filtered Mode) 26Hz 82Hz ±1.2mV ±2.2mV
Note: TME is the total measurement error.