LTC1569-6_1 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

LTC1569-6_1

Linear Phase, DC Accurate, Low Power, 10th Order Lowpass Filter

Linear Technology 

LTC1569-6

APPLICATIONS INFORMATION

Table 4. Clock Feedthrough

Power Supply

3V

5V

±5V

Feedthrough

0.1mVRMS

0.3mVRMS

0.9mVRMS

DC Accuracy

DC accuracy is defined as the error in the output voltage

after DC offset and DC gain errors are removed. This is

similar to the definition of the integral nonlinearity in A/D

converters. For example, after measuring values of VOUT(DC)

vs VIN(DC) for a typical LTC1569-6, a linear regression

shows that VOUT(DC) = VIN(DC) • 0.99854 + 0.00134V is the

straight line that best fits the data. The DC accuracy

describes how much the actual data deviates from this

straight line (i.e., DCERROR = VOUT(DC) – (VIN(DC) • 0.99854

+ 0.00134V). In a 12-bit system with a full-scale value of

2V, the LSB is 488µV. Therefore, if the DCERROR of the

filter is less than 488µV over a 2V range, the filter has

12-bit DC accuracy. Figure 9 illustrates the typical DC

accuracy of the LTC1569-6 on a single 5V supply.

DC Offset

The output DC offset of the LTC1569-6 is trimmed to less

than ±5mV. The trimming is performed with VS = 1.9V,

–1.1V with the filter cutoff frequency set to 4kHz (REXT =

10k, DIV/CLK shorted to V +). To obtain optimum DC offset

performance, appropriate PC layout techniques should be

used. The filter IC should be soldered to the PC board. The

power supplies should be well decoupled including a 1µF

ceramic capacitor from V + (Pin 7) to V – (Pin 4). A ground

plane should be used. Noisy signals should be isolated

from the filter input pins.

When the power supply is 3V, the output DC offset should

change less than ±2mV when the clock frequency varies

from 64kHz to 4096kHz. When the clock frequency is

fixed, the output DC offset will typically change by less

than ±3mV (±15mV) when the power supply varies from

3V to 5V (±5V) in the divide-by-1 mode. In the divide-by-

4 or divide-by-16 modes, the output DC offset will typically

change less than – 9mV (– 27mV) when the power supply

varies from 3V to 5V (±5V). The offset is measured with

respect to GND (Pin 3).

Aliasing

Aliasing is an inherent phenomenon of sampled data

filters. In lowpass filters significant aliasing only occurs

when the frequency of the input signal approaches the

sampling frequency or multiples of the sampling fre-

quency. The LTC1569-6 samples the input signal twice

every clock period. Therefore, the sampling frequency is

twice the clock frequency and 128 times the filter cutoff

frequency. Input signals with frequencies near 2 • fCLK

± fCUTOFF will be aliased to the passband of the filter and

appear at the output unattenuated.

IN– 2

+

IN+ – GND

–

i=

125k

–

125k

+

125k

IN+ 1

–

GND 3

+

Figure 8

8 OUT

1569-6 F06

488

244

0

–244

VS = 5V

REXT = 10k

TA = 25°C

–488

–1.5 –1.0 –0.5 0 0.5

VIN DC (V)

Figure 9

1.0 1.5

1569-6 F09

9

Share Link: