ISL26310 datasheet(14/23 Pages) RENESAS

14 / 23 page

ISL26310, ISL26311, ISL26312, ISL26313, ISL26314, ISL26315, ISL26319

FN7549 Rev 3.00

Page 14 of 23

August 18, 2015

Input Multiplexer

The input of the multiplexer connects the selected analog input

pins to the ADC input. A proprietary sampling circuit significantly

reduces the input drive requirements, resulting in lower overall

cost and board space in addition to improved performance. Note

that the input capacitance is only 2-3pF during the Sampling

phase, changing to 40pF during the Settling phase, resulting in

an average input current of 2.5µA and an effective input

capacitance of only 4pF (see Figure 26).

Voltage Reference Input

An external reference voltage must be supplied to the VREF pin to

set the full-scale input range of the converter. The VREF input on

these devices can accept voltages ranging from 2V (nominal) to

VDD, however, they are specified with VREF at a voltage of 5V with

VDD at 5V. Note that exceeding VDD by more than 100mV can

forward bias the ESD protection diodes and degrade measurement

accuracy due to leakage current. A lower value voltage reference

must be used if the device is operated with VDD at voltages lower

than 5V. If the VREF pin is tied to the VDD pin, the VREF pin should be

decoupled with a local 1µF ceramic capacitor as described in a later

paragraph.

Figures 27 and 28 illustrate possible voltage reference options

for these ADCs. Figure 27 uses the precision ISL21090 voltage

reference, which exhibits exceptionally low drift and low noise.

The ISL21090 must be powered from a supply greater than 4.7V.

Figure 28 illustrates the ISL21010 voltage reference used with

these ADCs. The ISL21010 series voltage references have higher

noise and drift than the ISL21090 devices, but operate at lower

supply voltages. Therefore, these devices can readily be used

when these SAR ADCs operate with VDD at voltages less than 5V.

The outputs of ISL21090 or the ISL21010 devices should be

decoupled with a 1µF ceramic capacitor. A 1µF, 6.3 V, X7R, 0603

(1608 metric) MLCC type capacitor is recommended for its high

frequency performance. The trace length from the VREF pin to

this capacitor and the voltage reference output should be as

short as possible.

The ISL26310 and ISL26313 devices (packaged in 8 pin SOIC

packages) derive their voltage reference from the VDD pin. To

achieve best performance, the VDD pin of these devices should

be bypassed with the 1µF ceramic capacitor mentioned above.

Power-Down/Standby Modes

In order to reduce power consumption between conversions, a

number of user-selectable modes can be utilized by setting the

appropriate bits in the Configuration Register.

Auto Power-down (PD0 = 0) reduces power consumption by

shutting down all portions of the device except the oscillator and

digital interface after completion of a conversion. There is a short

recovery period after CNV is asserted Low (150µs with external

reference).

In Auto Sleep mode (PD1 = 1), the device will automatically enter

the low-power Sleep mode at the end of the current conversion.

Recovery from this mode involves only 2.1µs and may offer an

alternative to Power-down mode in some applications.

Output Data Format

The converter output word is delivered in two’s complement

format in differential input mode, and straight binary in

single-ended input mode of operation respectively, all MSB-first.

Input exceeding the specified full-scale voltage results in a clipped

output which will not return to in-range values until after the input

signal has returned to the specified allowable voltage range.

Data must be read prior to the completion of the current

conversion to avoid conflict and loss of data, due to overwriting of

the new conversion data into the output register.

FIGURE 25. RELATIONSHIP BETWEEN VREF AND FULL-SCALE

RANGE FOR SINGLE-ENDED INPUTS

3.0

5.0

2.0

1.0

4.0

AIN

2.5Vp-p

VREF = 2.5V

3.0

5.0

2.0

1.0

4.0

AIN

5Vp-p

VREF = 5V

FIGURE 26. INPUT SAMPLING OPERATION

INPUT VOLTAGE

OFFSET ERROR

ERROR

TOTAL

ERROR

SETTLING ERROR AND NOISE

SAMPLING PHASE

SETTLING PHASE

ISL26310 Datasheet(PDF) 14 Page - Renesas Technology Corp

ISL26310 Datasheet(HTML) 14 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Datasheet Download

Link URL