Datasheet
MCP3911
DS20002286B-page 32 2012-2013 Microchip Technology Inc.
5.3.2 MODULATOR INPUT RANGE AND
SATURATION POINT
For a specified voltage reference value of 1.2V, the
modulator’s specified differential input range is
±600 mV. The input range is proportional to V
REF
and
scales according to the V
REF
voltage. This range is
ensuring the stability of the modulator over amplitude
and frequency. Outside of this range, the modulator is
still functional. However, its stability is no longer
ensured and therefore it is not recommended to exceed
this limit. See Figure 2-24 for extended dynamic range
performance limitations. The saturation point for the
modulator is V
REF
/1.5, since the transfer function of the
ADC includes a gain of 1.5 by default (independent
from the PGA setting. See Section 5.6 “ADC Output
Coding”).
5.3.3 BOOST SETTINGS
The Delta-Sigma modulators include a programmable
biasing circuit to further adjust the power consumption
to the sampling speed applied through the MCLK. This
can be programmed through the BOOST<1:0> bits,
which are applied to both channels simultaneously.
The maximum achievable analog master clock speed
(AMCLK) and the maximum sampling frequency
(DMCLK) and therefore, the maximum achievable data
rate (DRCLK), highly depend on BOOST<1:0> and
PGA_CHn<2:0> settings. Table 5-2 specifies the
maximum AMCLK possible to keep optimal accuracy in
function of BOOST<1:0> and PGA_CHn<2:0>
settings.
TABLE 5-2: MAXIMUM AMCLK LIMITS AS A FUNCTION OF BOOST AND PGA GAIN
Conditions V
DD
= 3.0V to 3.6V, T
A
from -40°C to +125°C V
DD
= 2.7V to 3.6V, T
A
from -40°C to +125°C
Boost Gain Maximum AMCLK
(MHz)
(SINAD within -3 dB
from its maximum)
Maximum AMCLK
(MHz)
(SINAD within -5 dB
from its maximum)
Maximum AMCLK
(MHz)
(SINAD within -3 dB
from its maximum)
Maximum AMCLK
(MHz)
(SINAD within -5 dB
from its maximum)
0.5x 1 3 3 3 3
0.66x 1 4 4 4 4
1x 1 10 10 10 10
2x 1 16 16 16 16
0.5x 2 2.5 3 3 3
0.66x 2 4 4 4 4
1x 2 10 10 10 10
2x 2 14.5 16 13.3 14.5
0.5x 4 2.5 2.5 2.5 2.5
0.66x 4 4 4 4 4
1x 4 10 10 8 10
2x 4 13.3 16 10.7 11.4
0.5x 8 2.5 2.5 2.5 2.5
0.66x 8 4 4 4 4
1x 8 10 11.4 6.7 8
2x 8 10 14.5 8 8
0.5x 16 2 2 2 2
0.66x 16 4 4 4 4
1x 16 10.6 10.6 8 10
2x 16 12.3 16 8 10.7
0.5x 32 2 2 2 2
0.66x 32 4 4 4 4
1x 32 10 11.4 8 10
2x 32 13.3 16 8 10