CS5467 datasheet(21/46 Pages) CIRRUS

21 / 46 page

CS5467

DS714A1

ADVANCE RELEASE

adding 2.737649x10-4 to the Temperature Offset Regis-

ter

(Toff). Therefore,

if Toff = -0.094488 and ∆T = -2.0 (°C), then

or 0xF3D5BB (2’s compliment notation) is stored in the

Temperature Offset Register

(Toff).

To convert the Temperature Register (T) from a Celsius

scale (°C) to a Fahrenheit scale (°F) utilize the formula

Applying the above relationship to the CS5461A tem-

perature measurement algorithm

If Toff = -0.09504 and Tgain = 26.443 for a Celsius scale,

the modified values are Toff = -0.09017 (0xF47550) and

Tgain = 47.6 (0x5F3333) for a Fahrenheit scale.

5.8 Voltage Reference

The CS5467 is specified for operation with a +2.5 V ref-

erence between the VREFIN and AGND pins. To utilize

the on-chip 2.5 V reference, connect the VREFOUT pin

to the VREFIN pin of the device. The VREFIN can be

used to connect external filtering and/or references.

5.9 System Initialization

Upon powering up, the digital circuitry is held in reset

until the analog voltage reaches 4.0 V. At that time, an

eight-XIN-clock-period delay is enabled to allow the os-

cillator to stabilize. The CS5467 will then initialize.

A hardware reset is initiated when the RESET pin is as-

serted with a minimum pulse width of 50 ns. The RE-

SET signal is asynchronous, with a Schmitt-trigger

input. Once the RESET pin is de-asserted, an

eight-XIN-clock-period delay is enabled.

A software reset is initiated by writing the command

0x80. After a hardware or software reset, the internal

registers (some of which drive output pins) will be reset

to their default values. Status bit DRDY in the Status

indicates the CS5467 is in its active state and

ready to receive commands.

5.10 Power-down States

The CS5467 has two power-down states, Stand-by and

Sleep

. In the stand-by state all circuitry except the volt-

age reference and crystal oscillator is turned off. To re-

turn the device to the active state, a power-up command

is sent to the device.

In Sleep state, all circuitry except the instruction decod-

er is turned off. When the power-up command is sent to

the device, a system initialization is performed (See

Section 5.9 System Initialization on page 21).

5.11 Oscillator Characteristics

XIN and XOUT are the input and output of an inverting

amplifier configured as an on-chip oscillator, as shown

in Figure 11. The oscillator circuit is designed to work

with a quartz crystal. To reduce circuit cost, two load ca-

pacitors C1 and C2 are integrated in the device, from

XIN to DGND, and XOUT to DGND. PCB trace lengths

should be minimized to reduce stray capacitance. To

drive the device from an external clock source, XOUT

should be left unconnected while XIN is driven by the

external circuitry. There is an amplifier between XIN and

the digital section which provides CMOS level signals.

This amplifier works with sinusoidal inputs so there are

no problems with slow edge times.

The CS5467 can be driven by an external oscillator

ranging from 2.5 to 20 MHz, but the K divider value must

be set such that the internal MCLK will run somewhere

between 2.5 MHz and 5 MHz. The K divider value is set

with the K[3:0] bits in the Configuration Register. As an

example, if XIN = MCLK = 15 MHz, and K is set to 5,

DCLK will equal 3 MHz, which is a valid value for DCLK.

5.12 Event Handler

The INT pin is used to indicate that an internal error or

event has taken place in the CS5467. Writing a logic 1

off

∆T 2.737649 10

–

⋅

()

off

0.094488

–

2.0

–

2.737649

–

⋅

()

0.09504

–

---C

17.7778

()

〈〉

--- T

gain

⎝⎠

⎛⎞ TC

〈〉

off

17.7778

2.737649

–

⋅

()

⎝⎠

⎛⎞

Oscillator

Circuit

DGND

XIN

XOUT

C1 =

22 pF

C2 =

Figure 11. Oscillator Connection

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