LTC2453_1 datasheet(11/18 Pages) LINER

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LTC2453

2453fb

Driving VCC and GND

In relation to the VCC and GND pins, the LTC2453 combines

internal high frequency decoupling with damping elements,

which reduce the ADC performance sensitivity to PCB

layout and external components. Nevertheless, the very

high accuracy of this converter is best preserved by careful

low and high frequency power supply decoupling.

A 0.1μF, high quality, ceramic capacitor in parallel with a

10μF ceramic capacitor should be connected between the

VCC and GND pins, as close as possible to the package.

The 0.1μF capacitor should be placed closest to the ADC

package. It is also desirable to avoid any via in the circuit

path, starting from the converter VCC pin, passing through

these two decoupling capacitors, and returning to the

converter GND pin. The area encompassed by this circuit

path, as well as the path length, should be minimized.

Very low impedance ground and power planes, and star

connections at both VCC and GND pins, are preferable.

The VCC pin should have three distinct connections: the

RSW

15k

(TYP)

ILEAK

VCC

CEQ

0.35pF

(TYP)

IN+

IN–

REF–

REF+

2453 F08

RSW

15k

(TYP)

ILEAK

RSW

15k

(TYP)

ILEAK

RSW

15k

(TYP)

ILEAK

Figure 8. LTC2453 Analog Input/Reference Equivalent Circuit

ILEAK

RSW

15k

(TYP)

ICONV

CIN

IN+

VCC

SIG+

SIG–

CEQ

0.35pF

(TYP)

CPAR

–

2453 F09

ILEAK

RSW

15k

(TYP)

ICONV

CIN

IN–

VCC

CEQ

0.35pF

(TYP)

CPAR

–

Figure 9. LTC2453 Input Drive Equivalent Circuit

ﬁrst to the decoupling capacitors described above, the

second to the ground return for the input signal source,

and the third to the ground return for the power supply

voltage source.

Driving REF+ and REF–

A simpliﬁed equivalent circuit for REF+ and REF– is shown

in Figure 8. Like all other A/D converters, the LTC2453 is

only as accurate as the reference it is using. Therefore, it

is important to keep the reference line quiet by careful low

and high frequency power supply decoupling.

The LT6660 reference is an ideal match for driving the

LTC2453’s REF+ pin. The LTC6660 is available in a 2mm

2mm DFN package with 2.5V, 3V, 3.3V and 5V options.

A 0.1μF, high quality, ceramic capacitor in parallel with

a 10μF ceramic capacitor should be connected between

the REF+/REF– and GND pins, as close as possible to the

package. The 0.1μF capacitor should be placed closest

to the ADC.

Driving VIN+ and VIN–

The input drive requirements can best be analyzed using

the equivalent circuit of Figure 9. The input signal VSIG is

connected to the ADC input pins (IN+ and IN–) through

an equivalent source resistance RS. This resistor includes

both the actual generator source resistance and any

additional optional resistors connected to the input pins.

APPLICATIONS INFORMATION

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