ADC 2 Especificações descarregar pdf (Página 23)

f =

-3dB

ln(2) 2´

2 16 tp ´ ´

CLK

ADS7865

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SBAS441C –OCTOBER 2008–REVISED APRIL 2012

ADS7862 COMPATIBILITY DAC properly via the DAC register while removing

the external resistors; or

The ADS7865IPBS is pin-compatible with the

• An additional external buffer between the resistor

ADS7862Y. However, there are some differences

divider and the required 470nF (minimum)

between the two devices that must be considered

capacitor on the REF

input.

when migrating from the ADS7862 to the ADS7865 in

an existing design.

In the latter case, while the capacitor stabilizes the

reference voltage during the entire conversion, the

WR versus A0

buffer must recharge it by providing an average

current only; thus, the required minimum bandwidth of

One of the differences is that pin 22, which triggers

the buffer can be calculated using Equation 2:

writing to the internal Configuration Register of the

ADS7865 (WR), is used to select the input channel

on the ADS7862 (A0).

(2)

Channel selection on the ADS7865 can only be

The buffer must also be capable of driving the 470nF

performed by setting bits C[1:0] in the Configuration

load while maintaining its stability.

Sequencer Register section for details).

Timing

REF

The only timing requirement that may cause the

ADS7865 to malfunction in an existing ADS7862-

The ADS7865 offers an unbuffered REF

input with a

based design is the CONVST low time (t

) which is

code-dependent input impedance while featuring a

specified to be 20ns minimum, while the ADS7862

programmable and buffered reference output

works properly with a pulse as short as 15ns. All

(REF

OUT

). The ADS7862 offers a high-impedance

other required minimum setup and hold times are

(buffered) reference input. If an existing ADS7862-

specified to be either the same as or lower than the

based design uses the internal reference of the

ADS7865; therefore, there are no conflicts with the

device and relies on an external resistor divider to

ADS7862 requirements.

adjust the input voltage range of the ADC, migration

to the ADS7865 platform requires one of the following

conditions:

• A software change to set up the internal reference

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