TL507C Datasheet, PDF (6/8 Pages) Texas Instruments – ANALOG-TO-DIGITAL CONVERTER

TL507C, TL507l
ANALOG-TO-DIGITAL CONVERTER
SLAS041 – OCTOBER 1979 – REVISED OCTOBER 1988
PRINCIPLES OF OPERATION
The TL507 is a single-slope analog-to-digital converter. All single-slope converters are basically voltage-to-time
or current-to-time converters. A study of the functional block diagram shows the versatility of the TL507.
An external clock signal is applied through a buffer to a negative-edge-triggered synchronous counter.
Binary-weighted resistors from the counter are connected to an operational amplifier used as an adder. The
operational amplifier generates a signal that ramps from 0.75 • V_CC1 down to 0.25 • V_CC1. Comparator 1
compares the ramp signal to the analog input signal. Comparator 2 functions as a fault defector. With the analog
input voltage in the range 0.25 • V_CC1 to 0.75 • V_CC1, the duty cycle of the output signal is determined by the
unknown analog input, as shown in Figure 2 and the Function Table.
For illustration, assume V_CC1 = 5.12 V,
0.25 • V_CC1 = 1.28 V
+ ^* + 1 binary count
(0.75 0.25) VCC1
128
20 mV
0.75 • V_CC1 – 1 count = 3.82 V
The output is an open-collector n-p-n transistor capable of withstanding up to 18 V in the off state. The output
is current limited to the 8- to 12-mA range; however, care must be taken to ensure that the output does not
exceed 5.5 V in the on state.
The voltage regulator section allows operation f rom either an unregulated 8- to 18-V V_CC2 source or a regulated
3.5- to 6-V V_CC1 source. Regardless of which external power source is used, the internal circuitry operates at
V_CC1. When operating from a V_CC1 source, V_CC2 may be connected to V_CC1 or left open. When operating from
a V_CC2 source, V_CC1 can be used as a reference voltage output.
Ramp Input to
Comparator 1
3.82 V
1.28 V
Analog Input
Level 1
Analog Input
Level 2
Output for
Input Level 1
Output for
Input Level 2
Figure 2
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