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ADS-238Q

12-Bit, 20MHz, Low Power Sampling A/D Converters

DATEL Data Acquisition products

ADS-238Q Datasheet PDF : 7 Pages

1 2 3 4 5 6 7

ADS-238Q

ABSOLUTE MAXIMUM RATINGS

PARAMETERS

LIMITS

Supply Voltage, VS (Pins 4-9,44)

Input Voltages:

Analog Input, VIN+, VIN–

(Pin 20, 21)

VREF–, VREF+, (Pin 10, 11)

CLK, (Pin 2)

Lead Temperature (10 seconds)

–0.5 to +6

–0.5 to (+VS +0.5)

+300

UNITS

Volts

°C

FUNCTIONAL SPECIFICATIONS

(TA = TMIN to TMAX, VS = 3.3V, VREF– = 1.15V, VREF+ = 2.15V, VCM = 1.65V, CLK

Frequency = 20MHz, BIAS1 = 90µA, BIAS2 = 9.5µA, Duty Cycle = 50% and

Differential Input, unless otherwise specified.)

ANALOG INPUTS

MIN. TYP. MAX. UNITS

Differential Input Voltage Range ±0.6

Common Mode Input Voltage

1.2

Input Capacitance

—

Input Bandwidth, Large Signal

—

±1.0

±1.7

Volts

1.65

1.9

Volts

1.4

—

120

—

MHz

DIGITAL INPUTS

Logic Levels

Logic "1"

Logic "0"

Logic Loading "1"

Logic Loading "0"

Input Capacitance

80% VS

—

Volts

— 20% VS Volts

—

±1

µA

—

±1

µA

1.8

—

REFERENCE VOLTAGES

Reference Input Voltage Range

(VREF+ - VREF–)

0.6

1.0

1.7

Volts

Negative Reference Voltage

(VREF–)

—

1.15

—

Volts

Positive Reference Voltage

(VREF+)

—

2.15

—

Volts

Common Mode Output Voltage

(VCM)

1.3

1.65

1.8

Volts

STATIC PERFORMANCE

Resolution

Differential Nonlinearity

Integral Nonlinearity

Common Mode rejection ratio

No Missing Codes

Offset, Mid-Scale

Gain Error

—

Bits

—

±0.6

—

LSB

—

±3.0

—

LSB

—

Bits

—

±1.0

—

%FSR

—

0.3

—

DYNAMIC PERFORMANCE

Peak Harmonics

FIN = 5MHz

FIN = 10MHz

Total Harmonics Distortion

FIN = 5MHz

FIN = 10MHz

Signal-to-Noise Ratio

(w/o distortion)

FIN = 5MHz

FIN = 10MHz

Signal-to-Noise Ratio

(and distortion)

FIN = 5MHz

FIN = 10MHz

Effective Number of Bits

FIN = 5MHz

FIN = 10MHz

—

–68

–61

—

–60

—

9.2

9.8

—

Bits

—

9.0

—

Bits

DYNAMIC PERFORMANCE

Differential Phase

Differential Gain

Aperature Uncertainty

Aperture Delay Time, tAP

Data Latency

A/D Conversion Rate

—

0.2

— Degrees

—

0.5

—

ps rms

—

7.5

—

Cycles

—

MHz

DIGITAL OUTPUTS

Logic "1"

80% VS 95% VS —

Volts

Logic "0"

—

0.1

0.4

Volts

CLK to Output Delay Time, tD

POWER REQUIREMENTS

Supply Voltages, VS

2.8

3.3

3.6

Volts

Supply Current, IS

—

Power Dissipation

—

100

Power Supply Rejection Ratio

—

PHYSICAL/ENVIRONMENTAL

Operating Temp. Range, Case

Storage Temperature Range

Package Type

Weight

—

+70

°C

–65

—

+125

°C

44-pin (leaded), plastic thin quad flat package

0.2 grams

TECHNICAL NOTES

Differential Analog Input

The analog input is a fully differential input that can be

configured in various ways depending on whether a single-

ended or differential, AC or DC coupled input is required.

An AC coupled input is most readily implemented using a

transformer (1:1 with a center tap on the secondary

winding) as illustrated in Figures 2, Typical Connection

Diagram, and 3.1, Transformer Coupled Input. To minimize

distortion, the core of the transformer must not saturate at

full scale input voltage levels. To minimize kickback noise

from the internal sample-hold a small capacitor should be

connected across the VIN pins (pins 20 and 21).

Figure 3.2, DC Coupled Single Ended Input, illustrates a

conversion circuit for a DC coupled single-ended input.

Power supplies and by-pass capacitors are not shown.

Reference Voltage Inputs

The ADS-238Q is designed to accept two external

reference voltages at the VREF input pins, see Figure 2,

Typical Connection Diagram. These reference voltages,

applied to VREF+ (pin 11) and VREF– (pin 10), determine the

analog input voltage range, which is equal to ±(VREF+ -

VREF–). This voltage range will be symmetric about the

common mode voltage, and for best performance should

be symmetrical about the midpoint of the supply voltage.

In order to minimize overall converter noise it is

recommended that the VREF pins be adequately bypassed

using a 4.7µF tantalum capacitor in parallel with a 0.01µF

ceramic capacitor. Locate the bypass capacitors as close

to the unit as possible.

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