Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsData collecting ICsData acquisition IC - AD converter (ADC) External , Internal TQFP 48

ADS1601

VREFP

50pF300W

VREFN

VREFP

VREFN

10 Fm

0.1 Fm

10 Fm 0.1 Fm

0.1 Fm

ADS1601

AGND

VREFP

VMID

VCAP

VREFN

ADS1601

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SBAS322D –DECEMBER 2004–REVISED OCTOBER 2011

REFERENCE INPUTS (VREFN, VREFP, VMID) EXTERNAL REFERENCE (REFEN = HIGH)

The ADS1601 can operate from an internal or To use an external reference, set the REFEN pin

external voltage reference. In either case, the high. This deactivates the internal generators for

reference voltage V

REF

is set by the differential VREFP, VREFN, and VMID, and saves

voltage between VREFN and VREFP: V

REF

= approximately 25mA of current on the analog supply

(VREFP – VREFN). VREFP and VREFN each use (AVDD). The voltages applied to these pins must be

two pins, which should be shorted together. VMID within the values specified in the Electrical

equals approximately 2.5V and is used by the Characteristics table. Typically, VREFP = 4V, VMID =

modulator. VCAP connects to an internal node and 2.5V, and VREFN = 1V. The external circuitry must

must also be bypassed with an external capacitor. be capable of providing both a dc and a transient

current. Figure 41 shows a simplified diagram of the

internal circuitry of the reference when the internal

INTERNAL REFERENCE (REFEN = LOW)

reference is disabled. As with the input circuitry,

To use the internal reference, set the REFEN pin low.

switches S

and S

open and close as shown by the

This activates the internal circuitry that generates the

timing in Figure 37.

reference voltages. The internal reference voltages

are applied to the pins. Good bypassing of the

reference pins is critical to achieve optimum

performance and is done by placing the bypass

capacitors as close to the pins as possible. Figure 40

shows the recommended bypass capacitor values.

Use high-quality ceramic capacitors for the smaller

values. Avoid loading the internal reference with

external circuitry. If the ADS1601 internal reference is

to be used by other circuitry, buffer the reference

voltages to prevent directly loading the reference

pins.

Figure 41. Conceptual Internal Circuitry for the

Reference When REFEN = High

Figure 42 shows the recommended circuitry for

driving these reference inputs. Keep the resistances

used in the buffer circuits low to prevent excessive

thermal noise from degrading performance. Layout of

these circuits is critical; be sure to follow good

high-speed layout practices. Place the buffers, and

especially the bypass capacitors, as close to the pins

as possible. VCAP is unaffected by the setting on

REFEN and must be bypassed when using the

internal or an external reference.

Figure 40. Reference Bypassing When Using the

Internal Reference