MCP3910 datasheet(60/90 Pages) MICROCHIP

60 / 90 page

MCP3910

DS20005116D-page 60

 2012-2020 Microchip Technology Inc.

8.2

Power Supply Design and

Bypassing

The MCP3910 device was designed to measure posi-

tive and negative voltages that might be generated by

a current-sensing device. This current-sensing device,

with a Common-mode voltage close to 0V, is referred to

as AGND, which is a shunt or Current Transformer (CT)

with burden resistors attached to ground. The high per-

formance and good flexibility that characterize this

ADC enable it to be used in other applications, as long

as the absolute voltage on each pin, referred to AGND,

stays in the -1V to +1V interval.

In any system, the analog ICs (such as references or

operational amplifiers) are always connected to the

analog ground plane. The MCP3910 should also be

considered as a sensitive analog component and con-

nected to the analog ground plane. The ADC features

two pairs of pins: AGND and AVDD, and DGND and

DVDD. For best performance, it is recommended to

keep the two pairs connected to two different networks

(Figure 8-2). This way, the design will feature two

ground traces and two power supplies (Figure 8-3).

This means the analog circuitry (including MCP3910)

and the digital circuitry (MCU) should have separate

power supplies, and return paths to the external ground

reference, as described in Figure 8-2.

An example of a typical power supply circuit, with differ-

ent lines for analog and digital power, is shown in

Figure 8-3. A possible split example is shown in

Figure 8-4, where the ground star connection can be

done at the bottom of the device with the exposed pad.

The split between analog and digital can be done under

the device; AVDD and DVDD can be connected together

with lines coming under the ground plane. Another

possibility, sometimes easier to implement in terms of

PCB layout, is to consider the MCP3910 as an analog

component, and therefore, to connect both AVDD and

DVDD together, and AGND and DGND together with a star

connection. In this scheme, the decoupling capacitors

may be larger due to the ripple on the digital power

supply (caused by the digital filters and the SPI interface

of the MCP3910) now causing glitches on the analog

power supply.

FIGURE 8-2:

All Analog and Digital

Return Paths Need to Stay Separate with Proper

Bypass Capacitors.

FIGURE 8-3:

Power Supply with Separate Lines for Analog Section and Digital Section. Note the

“Net Tie” Object NT2 that Represents the Start Ground Connection.

“Star” Point

D- =

A- =

0.1 μF

MCU

AVDD DVDD

AGND DGND

MCP39XX

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