Linear Technology LTC6804-1 - Expanding the Number of Auxiliary Measurements; Internal Protection Features; Filtering of Cell and GPIO Inputs

LTC6804-1/LTC6804-2
60
680412fc
For more information www.linear.com/LTC6804-1
S0
S1
S2
S3
S4
S5
S6
S7
V
CC
SCL
SDA
A0
A1
GND
V
EE
D
O
ANALOG1
ANALOG2
ANALOG3
ANALOG4
ANALOG5
ANALOG6
ANALOG7
ANALOG8
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LTC1380
S0
S1
S2
S3
S4
S5
S6
S7
V
CC
SCL
SDA
A0
A1
GND
V
EE
D
O
ANALOG9
ANALOG10
ANALOG11
ANALOG12
ANALOG13
ANALOG14
ANALOG15
ANALOG16
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LTC1380
3
27
31
32
33
37
5
1µF
10nF
680412 F32
V
REG
GPIO5(SCL)
GPIO4(SDA)
V
–
GPIO1
LTC6804
4.7k
4.7k
1
2
4
–
+
LTC6255
100Ω
ANALOG INPUTS: 0.04V TO 4.5V
applicaTions inForMaTion
EXPANDING THE NUMBER OF AUXILIARY
MEASUREMENTS
The LTC6804 provides five GPIO pins, each of which is
capable of performing as an ADC input. In some applica
-
tions there is need to measure more signals than this, so
one means of
supporting higher signal count is to add
a MUX circuit such as shown in Figure 32. This circuit
digitizes up to sixteen source signals using the GPIO1
ADC input and MUX control is provided by two other
GPIO lines configured as an I
2
C port. The buffer amplifier
provides for fast settling of the selected signal to increase
the usable conversion rate.
INTERNAL PROTECTION FEATURES
The LTC6804 incorporates various ESD safeguards to en
-
sure a robust performance. An equivalent circuit showing
the specific protection structures is shown in Figure
33
.
While pins 43 to 48 have different functionality for the
-1 and -2 variants, the protection structure is the same.
Zener-like suppressors are shown with their nominal clamp
voltage, other diodes exhibit standard PN junction behavior.
Figure 32. MUX Circuit Supports Sixteen Additional Analog Measurements
Figure 33. Internal ESD Protection Structure of LTC6804
FILTERING OF CELL AND GPIO INPUTS
The LTC6804 uses a delta-sigma ADC, which has delta-
sigma modulator followed by a SINC3 finite impulse
response (FIR) digital filter. This greatly reduces input
filtering requirements. Furthermore, the programmable
oversampling ratio allows the user to determine the best
trade-off between measurement speed and filter cutoff
frequency. Even with this high order lowpass filter, fast
transient noise can still induce some residual noise in mea
-
surements, especially in the faster conversion modes. This
can be minimized by adding an RC lowpass decoupling to
each ADC input, which also helps reject potentially damag
-
ing high energy transients. Adding more than about 100Ω
to the ADC inputs begins to introduce a systematic error
in the measurement, which can be improved by raising
the filter capacitance or mathematically compensating in
software with a calibration procedure. For situations that
demand the highest level of battery voltage ripple rejec
-
tion, grounded capacitor filtering is recommended. This
configuration has a series resistance and capacitors that
decouple HF noise to V
–
. In systems where noise is less