MAX1230(2003) Ver la hoja de datos (PDF) - Maxim Integrated

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MAX1230
(Rev.:2003)

12-Bit 300ksps ADCs with FIFO, Temp Sensor, Internal Reference

Maxim Integrated 

12-Bit 300ksps ADCs with FIFO,

Temp Sensor, Internal Reference

AIN0-AIN15

(SINGLE ENDED);

AIN0, AIN2,

AIN4…AIN14

(DIFFERENTIAL)

HOLD

GND

(SINGLE ENDED);

AIN1, AIN3,

AIN5…AIN15

(DIFFERENTIAL)

REF

GND

DAC

CIN+

CIN-

HOLD

VDD/2

COMPARATOR

+

-

HOLD

Figure 3. Equivalent Input Circuit

appropriate bit of the bipolar or unipolar register.

Unipolar mode sets the differential input range from 0 to

VREF. A negative differential analog input in unipolar

mode causes the digital output code to be zero.

Selecting bipolar mode sets the differential input range

to ±VREF / 2. The digital output code is binary in unipo-

lar mode and two’s complement in bipolar mode. (See

the transfer function graphs, Figures 8 and 9.)

In single-ended mode, the MAX1226/MAX1228/

MAX1230 always operate in unipolar mode. The analog

inputs are internally referenced to GND with a full-scale

input range from 0 to VREF.

True Differential Analog Input T/H

The equivalent circuit of Figure 3 shows the

MAX1226/MAX1228/MAX1230s’ input architecture. In

track mode, a positive input capacitor is connected to

AIN0–AIN15 in single-ended mode (and AIN0, AIN2,

AIN4…AIN14 in differential mode). A negative input

capacitor is connected to GND in single-ended mode

(or AIN1, AIN3, AIN5…AIN15 in differential mode). For

external track-and-hold timing, use clock mode 01.

After the T/H enters hold mode, the difference between

the sampled positive and negative input voltages is

converted. The time required for the T/H to acquire an

input signal is determined by how quickly its input

capacitance is charged. If the input signal’s source

impedance is high, the required acquisition time length-

ens. The acquisition time, tACQ, is the maximum time

needed for a signal to be acquired, plus the power-up

time. It is calculated by the following equation:

( ) tAQC = 9 x RS + RIN x 24pF + tPWR

where RIN = 1.5kΩ, RS is the source impedance of the

input signal, and tPWR = 1µs, the power-up time of the

device. The varying power-up times are detailed in the

explanation of the clock mode conversions.

tACQ is never less than 1.4µs, and any source imped-

ance below 300Ω does not significantly affect the

ADC’s AC performance. A high-impedance source can

be accommodated either by lengthening tACQ or by

placing a 1µF capacitor between the positive and neg-

ative analog inputs.

Internal FIFO

The MAX1226/MAX1228/MAX1230 contain a FIFO

buffer that can hold up to 16 ADC results plus one tem-

perature result. This allows the ADC to handle multiple

internally clocked conversions and a temperature mea-

surement, without tying up the serial bus.

If the FIFO is filled and further conversions are request-

ed without reading from the FIFO, the oldest ADC

results are overwritten by the new ADC results. Each

result contains 2 bytes, with the MSB preceded by 4

leading zeros. After each falling edge of CS, the oldest

available byte of data is available at DOUT, MSB first.

When the FIFO is empty, DOUT is zero.

The first 2 bytes of data read out after a temperature mea-

surement always contain the temperature result preceded

by 4 leading zeros, MSB first. If another temperature mea-

surement is performed before the first temperature result

is read out, the old measurement is overwritten by the

new result. Temperature results are in degrees Celsius

(two’s complement) at a resolution of 1/8 of degree. See

the Temperature Measurements section for details on

converting the digital code to a temperature.

Internal Clock

The MAX1226/MAX1228/MAX1230 operate from an inter-

nal oscillator, which is accurate within 10% of the 4.4MHz

nominal clock rate. The internal oscillator is active in clock

modes 00, 01, and 10. Read out the data at clock speeds

up to 10MHz. See Figures 4–7 for details on timing speci-

fications and starting a conversion.

Applications Information

Register Descriptions

The MAX1226/MAX1228/MAX1230 communicate

between the internal registers and the external circuitry

through the SPI-/QSPI-compatible serial interface.

Table 1 details the registers and the bit names. Tables

2–7 show the various functions within the conversion

register, setup register, averaging register, reset regis-

ter, unipolar register, and bipolar register.

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