AS1524/AS1525
Datasheet - Detailed Description
Input Bandwidth
The AS1524/AS1525 input tracking circuitry has a 20MHz small signal bandwidth, so it is possible to digitize high-
speed transient events and measure periodic signals with bandwidths exceeding the AS1524/AS1525 sampling rate
by using undersampling techniques.
Note: To avoid high-frequency signals being aliased into the frequency band of interest, anti-alias filtering is recom-
mended.
Analog Input Protection
Internal protection diodes that clamp the analog input to VDD and GND allow the analog input pins to swing from GND
- 0.3V to VDD + 0.3V without damage. Both inputs must not exceed VDD by more than 50mV or be lower than GND by
more than 50mV for accurate conversions.
Note: If an off-channel analog input voltage exceeds the supply voltages, the input current should be limited to 2mA.
Internal Clock
The AS1524/AS1525 operate from an internal clock, which is accurate within 5% of the 4MHz clock rate. This results in
a worst-case conversion time of 3.7µs. The internal clock releases the system microprocessor from running the SAR
conversion clock and allows the conversion results to be read back at the processor’s convenience, at any clock rate
from 0 to 8MHz.
Output Data Format
Figure 19 on page 12 and Figure 20 on page 12 illustrate the conversion timing for the AS1524/AS1525. The 12-bit
conversion result is output in MSB-first format. Data on DOUT transitions on the falling edge of SCLK. All 12 bits must
be clocked out before CNVST transitions again.
For the AS1524, data is straight binary for unipolar mode and two’s complement for bipolar mode. For the AS1525,
data is always straight binary.
Transfer Function
Figure 21 on page 13 shows the unipolar transfer function for the AS1524/AS1525. Figure 22 on page 14 shows the
bipolar transfer function for the AS1524. Code transitions occur halfway between successive-integer LSB values.
Figure 21. AS1524/AS1525 Unipolar Transfer Function
Full Scale = VREF
Zero Scale = GND
1 LSB = VREF/4096
Transition
Full-Scale
11...111
11...110
11....101
00...011
00...010
00...001
00...000
0
1
2
3
FS-3/2 LSB FS
Input Voltage (LSB)
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