Datasheet

AIN1
AIN8
.
.
.
MICROPROCESSOR
DSP
SCLK
CS
DIN
DOUT
AGND
AV
DD
DV
DD
ADC78H90
LP2950
5V
100:
0.1 PF
680 nF
1 PF
TANT
0.1 PF 0.1 PF1 PF
DGND
ADC78H90
SNAS227D –NOVEMBER 2003–REVISED MARCH 2013 www.ti.com
ADC78H90 TRANSFER FUNCTION
The output format of the ADC89H90 is straight binary. Code transitions occur midway between successive
integer LSB values. The LSB width for the ADC78H90 is AV
DD
/ 4096. The ideal transfer characteristic is shown
in Figure 23. The transition from an output code of 0000 0000 0000 to a code of 0000 0000 0001 is at 1/2 LSB,
or a voltage of AV
DD
/ 8192. Other code transitions occur at steps of one LSB.
Figure 23. Ideal Transfer Characteristic
TYPICAL APPLICATION CIRCUIT
A typical application of the ADC78H90 is shown in Figure 24. The split analog and digital supplies are both
provided in this example by the TI LP2950 low-dropout voltage regulator, available in a variety of fixed and
adjustable output voltages. The analog supply is bypassed with a capacitor network located close to the
ADC78H90. The digital supply is separated from the analog supply by an isolation resistor and conditioned with
additional bypass capacitors. The ADC78H90 uses the analog supply (AV
DD
) as its reference voltage, so it is
very important that AV
DD
be kept as clean as possible. Because of the ADC78H90's low power requirements, it is
also possible to use a precision reference as a power supply to maximize performance. The four-wire interface is
also shown connected to a microprocessor or DSP.
Figure 24. Typical Application Circuit
14 Submit Documentation Feedback Copyright © 2003–2013, Texas Instruments Incorporated
Product Folder Links: ADC78H90