MCP3906 datasheet(12/26 Pages) MICROCHIP

12 / 26 page

MCP3905/06

DS21948C-page 12

4.1

Analog Inputs

The MCP3905/06 analog inputs can be connected

directly to the current and voltage transducers (such as

shunts or current transformers). Each input pin is

protected by specialized Electrostatic Discharge (ESD)

structures that are certified to pass 5 kV HBM and

500V MM contact charge. These structures also allow

up to ±6V continuous voltage to be present at their

inputs without the risk of permanent damage.

Both channels have fully differential voltage inputs for

better noise performance. The absolute voltage at each

pin relative to AGND should be maintained in the ±1V

range during operation in order to ensure the measure-

ment error performance. The common mode signals

should be adapted to respect both the previous

conditions and the differential input voltage range. For

best performance, the common mode signals should

be referenced to AGND.

The current channel comprises a PGA on the front-end

to allow for smaller signals to be measured without

additional signal conditioning. The maximum differen-

tial voltage specified on Channel 0 is equal to

±470 mV/Gain (see Table 4-1). The maximum peak

voltage specified on Channel 1 is equal to ±660 mV.

4.2

16-Bit Delta-Sigma ADCs

The ADCs used in the MCP3905/06 for both current

and voltage channel measurements are delta-sigma

ADCs. They comprise a second-order, delta-sigma

modulator using a multi-bit DAC and a third-order SINC

filter. The delta-sigma architecture is very appropriate

for the applications targeted by the MCP3905, because

it is a waveform-oriented converter architecture that

can offer both high linearity and low distortion perfor-

mance throughout a wide input dynamic range. It also

creates minimal requirements for the anti-aliasing filter

design. The multi-bit architecture used in the ADC

minimizes quantization noise at the output of the

converters without disturbing the linearity.

Both ADCs have a 16-bit resolution, allowing wide input

dynamic range sensing. The oversampling ratio of both

converters is 64. Both converters are continuously

converting during normal operation. When the MCLR

pin is low, both converters will be in Reset and output

code 0x0000h. If the voltage at the inputs of the ADC is

larger than the specified range, the linearity is no longer

specified. However, the converters will continue to

produce output codes until their saturation point is

reached. The DC saturation point is around 700 mV for

Channel 0 and 1V for Channel 1, using internal voltage

reference.

The clocking signals for the ADCs are equally distrib-

uted between the two channels in order to minimize

phase delays to less than 1 MCLK period (see

Section 3.2 “High-Pass Filter Input Logic Pin

(HPF)”). The SINC filters main notch is positioned at

MCLK/256 (14 kHz with MCLK = 3.58 MHz), allowing

the user to be able to measure wide harmonic content

on either channel. The magnitude response of the

SINC filter is shown in Figure 4-2.

FIGURE 4-2:

SINC Filter Magnitude

Response (MCLK = 3.58 MHz).

4.3

Ultra-Low Drift VREF

The MCP3905/06 contains an internal voltage refer-

ence source specially designed to minimize drift over

temperature. This internal VREF supplies reference

voltage to both current and voltage channel ADCs. The

typical value of this voltage reference is 2.4V, ±100 mV.

The internal reference has a very low typical tempera-

ture coefficient of ±15 ppm/°C, allowing the output

frequencies to have minimal variation with respect to

temperature since they are proportional to (1/VREF)².

REFIN/OUT is the output pin for the voltage reference.

Appropriate bypass capacitors must be connected to

the

REFIN/OUT

for

proper

operation

(see

Section 5.0

“Applications

Information”).

The

voltage reference source impedance is typically 4 k

Ω,

which enables this voltage reference to be overdriven

by an external voltage reference source.

TABLE 4-1:

MCP3905 GAIN SELECTIONS

CH0 Gain

Maximum

CH0 Voltage

1±470 mV

2±235 mV

8±60 mV

±30 mV

TABLE 4-2:

MCP3906 GAIN SELECTIONS

CH0 Gain

Maximum

CH0 Voltage

1±470 mV

±15 mV

8±60 mV

±30 mV

-120

-100

-80

-60

-40

-20

Frequency (kHz)

MCP3906 Datasheet(PDF) 12 Page - Microchip Technology

MCP3906 Datasheet(HTML) 12 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL