CS5510-ASZ datasheet(20/26 Pages) CIRRUS

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CS5510/11/12/13

DS337F4

priate time during the third conversion cycle to en-

sure the maximum possible throughput.

2.6

Digital Off-chip System

Calibration

The CS5510/11/12/13 exhibit excellent linearity

with low offset and gain drift, without the need for

calibration. If precision voltage measurements are

required by the system, however, software-based

offset and gain calibration can be performed by the

system.

To perform a software offset calibration, the “zero-

point” of the system should be established by ap-

plying an input to the system equal to zero. Then,

the user can obtain a conversion and store it in

memory as the system’s zero point (ZP). This num-

ber can then be used as the zero point for any sub-

sequent conversion words. In the 20-bit devices

(CS5512 and CS5513), multiple conversions can

be averaged to arrive at a more accurate offset val-

ue. In the 16-bit devices (CS5510 and CS5511),

averaging may not be meaningful, because the

noise will be below the size of one LSB when using

nominal voltages for VREF (2.5 V).

A software gain calibration can be performed by

bringing the system to a known calibration Voltage

value (Vcal) and acquiring a conversion (note that

Vcal should be low enough to compensate for the

possible gain error of the ADC). Multiple conver-

sions can be averaged at this point to improve the

accuracy of the calibration. The code obtained

from this conversion is the real value (Cr) of the

calibration Voltage input, and will differ from the

ideal value. The ideal value for this conversion (Ci)

will be equivalent to: 0x7FFF*Vcal/(0.80*Vref) for

the CS5510/11, and 0x7FFFF*Vcal/(0.80*Vref) for

the CS5512/13. The gain error (GE) is equal to: (Cr

- ZP)/Ci. To correct for both offset and gain error in

subsequent conversions, subtract the offset error,

and then divide by the gain error.

2.7

Power Consumption, Sleep and

Reset

The CS5510/11/12/13 accommodates two power

modes: normal and sleep. The normal mode is the

default mode and is entered after power is estab-

lished to the ADC. In normal mode, the ADCs typ-

ically consumes 2.5 mW. Sleep is entered when

the user leaves SCLK high for at least 200

μs. The

ADCs are guaranteed to be in sleep after SCLK is

high (logic 1) for 2 ms. The sleep mode reduces

the consumed power to less than 10

μW when CS

is high (logic 1). If CS is low (logic 0) at this time,

the SDO drive logic will still be active, and the con-

sumed sleep power will be greater. To exit sleep

and return to normal mode, the user must return

SCLK low for at least 10

μs. After a sleep is exited,

the ADCs reset all their internal logic, including

their digital filters, and begin performing conver-

sions. Since the filters are reset, the first three con-

version after returning to normal mode will not be

fully settled.

2.8

PCB Layout

The CS5510/11/12/13 should be placed entirely

over the analog ground. Place the analog-digital

plane split immediately adjacent to the digital pins

of the chip.

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