Datasheet LTC1040 (Analog Devices) - 8
| Fabricante | Analog Devices |
| Descripción | Dual Micropower Comparator |
| Páginas / Página | 12 / 8 — APPLICATIO S I FOR ATIO. Output Logic. Using Internal Strobe. Table 1. … |
| Formato / tamaño de archivo | PDF / 227 Kb |
| Idioma del documento | Inglés |
APPLICATIO S I FOR ATIO. Output Logic. Using Internal Strobe. Table 1. Output Logic Truth Table. A INPUTS. B INPUTS. OUT. BOUT. A + B
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LTC1040
U U W U APPLICATIO S I FOR ATIO Output Logic
Because of the sampling nature of the LTC1040, some sensitivity exists between the offset voltage and the falling In addition to the normal outputs (AOUT and BOUT), two edge of the input strobe. When the falling edge of the additional outputs, A + B and ON/0FF, are provided (see strobe signal falls within the comparator’s active time Figure 8 and Table 1). All logic is powered from V+ and (80µs after rising edge), offset changes of as much as 2mV ground, thus input and output logic levels are independent can occur. To eliminate this problem, make sure the strobe of the V – supply. The LTC1040 is directly compatible with pulse width is greater than the response time, t CMOS logic and is TTL compatible for 4.75V ≤ V+ ≤ 5.25V. D. No external pull-up resistors are required.
Using Internal Strobe Table 1. Output Logic Truth Table
An internal oscillator allows the LTC1040 to strobe itself. Σ
A INPUTS
Σ
B INPUTS A
The frequency of oscillation, and hence sampling rate, is
OUT BOUT A + B ON/OFF
set by an external RC network (see typical curve of + + H H L L Sampling Rate vs R + – H L L L EXT, CEXT). – + L H L H For self-oscillation, the STROBE pin must be tied to – – L L H I* ground. The external RC network is connected as shown *I = indeterminate. When both A and B outputs are low, the ON/OFF output in Figure 9. remains in the state it was in prior to entering AOUT = BOUT = L. To assure oscillation, REXT must be between 100k and
Using External Strobe
10M. There is no limit to the size of CEXT. A positive pulse on the strobe input, with the 0SC input tied REXT is very important in determining the power to ground, will initiate a comparison cycle. The STROBE consumption. The average voltage at the oscillator pin is input is edge-sensitive and pulse widths of 50ns will approximately V+/2. The power consumed by REXT is then: typically trigger the device. PREXT = (V +/2)2/REXT. V+ 1 18 2 ON/OFF 17 REXT 16 CEXT LTC1040 COMPARATOR A D OUTPUT C Q 4 AOUT A + B 9 10 COMPARATOR B 3 D OUTPUT C Q 15 BOUT LTC1040 • AI09 STROBE
Figure 9. External RC Connection
Example: REXT = 1M, V + 5V, PREXT = (2.5)2/106 = 6.25 • 10–6W. 80µs LTC1040 • AI08 This is about four times the power consumed by the LTC1040 at V + = 5V and fS = 1 sample/second. Where
Figure 8. LTC1040 Logic Diagram
power is a premium REXT should be made as large as possible. Note that the power consumed by REXT is not a function of fS or CEXT. 1040fa 8
U U W U APPLICATIO S I FOR ATIO Output Logic
Because of the sampling nature of the LTC1040, some sensitivity exists between the offset voltage and the falling In addition to the normal outputs (AOUT and BOUT), two edge of the input strobe. When the falling edge of the additional outputs, A + B and ON/0FF, are provided (see strobe signal falls within the comparator’s active time Figure 8 and Table 1). All logic is powered from V+ and (80µs after rising edge), offset changes of as much as 2mV ground, thus input and output logic levels are independent can occur. To eliminate this problem, make sure the strobe of the V – supply. The LTC1040 is directly compatible with pulse width is greater than the response time, t CMOS logic and is TTL compatible for 4.75V ≤ V+ ≤ 5.25V. D. No external pull-up resistors are required.
Using Internal Strobe Table 1. Output Logic Truth Table
An internal oscillator allows the LTC1040 to strobe itself. Σ
A INPUTS
Σ
B INPUTS A
The frequency of oscillation, and hence sampling rate, is
OUT BOUT A + B ON/OFF
set by an external RC network (see typical curve of + + H H L L Sampling Rate vs R + – H L L L EXT, CEXT). – + L H L H For self-oscillation, the STROBE pin must be tied to – – L L H I* ground. The external RC network is connected as shown *I = indeterminate. When both A and B outputs are low, the ON/OFF output in Figure 9. remains in the state it was in prior to entering AOUT = BOUT = L. To assure oscillation, REXT must be between 100k and
Using External Strobe
10M. There is no limit to the size of CEXT. A positive pulse on the strobe input, with the 0SC input tied REXT is very important in determining the power to ground, will initiate a comparison cycle. The STROBE consumption. The average voltage at the oscillator pin is input is edge-sensitive and pulse widths of 50ns will approximately V+/2. The power consumed by REXT is then: typically trigger the device. PREXT = (V +/2)2/REXT. V+ 1 18 2 ON/OFF 17 REXT 16 CEXT LTC1040 COMPARATOR A D OUTPUT C Q 4 AOUT A + B 9 10 COMPARATOR B 3 D OUTPUT C Q 15 BOUT LTC1040 • AI09 STROBE
Figure 9. External RC Connection
Example: REXT = 1M, V + 5V, PREXT = (2.5)2/106 = 6.25 • 10–6W. 80µs LTC1040 • AI08 This is about four times the power consumed by the LTC1040 at V + = 5V and fS = 1 sample/second. Where
Figure 8. LTC1040 Logic Diagram
power is a premium REXT should be made as large as possible. Note that the power consumed by REXT is not a function of fS or CEXT. 1040fa 8