CY8C52 datasheet(46/94 Pages) CYPRESS

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PRELIMINARY

PSoC® 5: CY8C52 Family Datasheet

Document Number: 001-66236 Rev. **

Page 46 of 94

Analog local buses (abus) are routing resources located within

the analog subsystem and are used to route signals between

different analog blocks. There are eight abus routes in CY8C38,

four in the left half (abusl [0:3]) and four in the right half (abusr

[0:3]) as shown in Figure 8-2. Using the abus saves the analog

globals and analog mux buses from being used for

interconnecting the analog blocks.

Multiplexers and switches exist on the various buses to direct

signals into and out of the analog blocks. A multiplexer can have

only one connection on at a time, whereas a switch can have

multiple connections on simultaneously. In Figure 8-2,

multiplexers are indicated by grayed ovals and switches are

indicated by transparent ovals.

8.2 Successive Approximation ADC

The CY8C52 family of devices has a SAR ADC. This ADC is

12-bit at up to 1 Msps, with single-ended or differential inputs,

making it useful for a wide variety of sampling and control

applications.

8.2.1 Functional Description

In a SAR ADC an analog input signal is sampled and compared

with the output of a DAC. A binary search algorithm is applied to

the DAC and used to determine the output bits in succession

from MSB to LSB. A block diagram of the SAR ADC is shown in

Figure 8-3.

Figure 8-3. SAR ADC Block Diagram

The input is connected to the analog globals and muxes. The

frequency of the clock is 16 times the sample rate; the maximum

clock rate is 16 MHz.

8.2.2 Conversion Signals

Writing a start bit or assertion of a start of frame (SOF) signal is

used to start a conversion. SOF can be used in applications

where the sampling period is longer than the conversion time, or

when the ADC needs to be synchronized to other hardware. This

signal is optional and does not need to be connected if the SAR

ADC is running in a continuous mode. A digital clock or UDB

output can be used to drive this input. When the SAR is first

powered up or awakened from any of the sleeping modes, there

is a power up wait time of 10 µs before it is ready to start the first

conversion.

When the conversion is complete, a status bit is set and the

output signal end of frame (EOF) asserts and remains asserted

until the value is read by either the DMA controller or the CPU.

The EOF signal may be used to trigger an interrupt or a DMA

request.

8.2.3 Operational Modes

A ONE_SHOT control bit is used to set the SAR ADC conversion

mode to either continuous or one conversion per SOF signal.

DMA transfer of continuous samples, without CPU intervention,

is supported.

8.3 Comparators

The CY8C52 family of devices contains two comparators in a

device. Comparators have these features:

Input offset factory trimmed to less than 5 mV

Rail-to-rail common mode input range (VSSA to VCCA)

Speed and power can be traded off by using one of three

modes: fast, slow, or ultra low power

Comparator outputs can be routed to look up tables to perform

simple logic functions and then can also be routed to digital

blocks

The positive input of the comparators may be optionally passed

through a low pass filter. Two filters are provided

Comparator inputs can be connected to GPIO or DAC output

8.3.1 Input and Output Interface

The positive and negative inputs to the comparators come from

the analog global buses, the analog mux line, the analog local

bus and precision reference through multiplexers. The output

from each comparator could be routed to any of the two input

LUTs. The output of that LUT is routed to the UDB digital system

interface.

S/H

DAC

array

vin

vrefp

vrefn

comparator

SAR

digital

D0:D11

clock

autozero

reset

clock

power

filtering

POWER

GROUND

vrefp

vrefn

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