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LTC2326-16

232616fa

For more information www.linear.com/LTC2326-16

applicaTions inForMaTion

Figure 5a. LTC2326-16 Internal Reference Circuit

Table 1. Internal Reference with Internal Buffer

REFIN

REFBUF

BIPOLAR INPUT RANGE

2.048V

4.096V

±10.24V

Table 2. External Reference with Internal Buffer

REFIN

(OVERDRIVE)

REFBUF

BIPOLAR INPUT RANGE

1.25V (Min)

2.5V

±6.25V

2.048V

4.096V

±10.24V

2.4V (Max)

4.8V

±12V

Table 3. External Reference Unbuffered

REFIN

REFBUF

(OVERDRIVE)

BIPOLAR INPUT RANGE

2.5V (Min)

±6.25V

5V (Max)

±12.5V

Internal Reference with Internal Buffer

The LTC2326-16 has an on-chip, low noise, low drift

(20ppm/°C max), temperature compensated bandgap

reference that is factory trimmed to 2.048V. It is internally

connected to a reference buffer as shown in Figure 5a and

is available at REFIN (Pin 8). REFIN should be bypassed to

GNDwitha100nFceramiccapacitortominimizenoise.The

reference buffer gains the REFIN voltage by 2 to 4.096V at

REFBUF (Pin 7). So the input range is ±10.24V, as shown

in Table 1. Bypass REFBUF to GND with at least a 47μF

ceramic capacitor (X7R, 10V, 1210 size) to compensate

the reference buffer and minimize noise.

External Reference with Internal Buffer

If more accuracy and/or lower drift is desired, REFIN

can be easily overdriven by an external reference since

a 15k resistor is in series with the reference as shown

in Figure 5b. REFIN can be overdriven in the range from

1.25V to 2.4V. The resulting voltage at REFBUF will be

2 • REFIN. So the input range is ±5 • REFIN, as shown

in Table 2. Linear Technology offers a portfolio of high

performance references designed to meet the needs of

manyapplications.Withitssmallsize,lowpower,andhigh

accuracy, the LTC6655-2.048 is well suited for use with

the LTC2326-16 when overdriving the internal reference.

The LTC6655-2.048 offers 0.025% (max) initial accuracy

and 2ppm/°C (max) temperature coefficient for high pre-

cision applications. The LTC6655-2.048 is fully specified

over the H-grade temperature range and complements

the extended temperature range of the LTC2326-16 up to

125°C.BypassingtheLTC6655-2.048witha2.7μFto100µF

ceramic capacitor close to the REFIN pin is recommended.

External Reference Unbuffered

The internal reference buffer can also be overdriven from

2.5V to 5V with an external reference at REFBUF as shown

in Figure 5c. So the input ranges are ±6.25V to ±12.5V,

respectively, as shown in Table 3. To do so, REFIN must

be grounded to disable the reference buffer. A 13k resistor

loadstheREFBUFpinwhenthereferencebufferisdisabled.

To maximize the input signal swing and corresponding

SNR, the LTC6655-5 is recommended when overdriv-

ing REFBUF. The LTC6655-5 offers the same small size,

accuracy, drift and extended temperature range as the

LTC6655-2.048. By using this 5V reference, an SNR of

94.5dB can be achieved. Bypassing the LTC6655-5 with

a 47μF ceramic capacitor (X5R, 0805 size) close to the

REFBUF pin is recommended.

TheREFBUFpinoftheLTC2326-16drawsacharge(QCONV)

fromtheexternalbypasscapacitorduringeachconversion

cycle. If the internal reference buffer is overdriven, the

external reference must provide all of this charge with a

DC current equivalent to IREFBUF = QCONV/tCYC. Thus, the

DC current draw of REFBUF depends on the sampling

LTC2326-16

BANDGAP

REFERENCE

232616 F05a

47µF

100nF

6.5k

REFBUF

REFIN

15k

6.5k

REFERENCE

BUFFER

GND

–

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