SLCS160 June 2017 LM139-MIL
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Validate and test the design implementation to confirm system functionality.
8.1 Application Information
Typically, a comparator compares either a single signal to a reference, or to two different signals. Many users take advantage of the open-drain output to drive the comparison logic output to a logic voltage level to an MCU or logic device. The wide supply range and high voltage capability makes the LM139-MIL device optimal for level shifting to a higher or lower voltage.
8.2 Typical Application
Figure 7. Single-Ended and Differential Comparator Configurations
8.2.1 Design Requirements
For this design example, use the parameters listed in Table 1 as the input parameters.
Table 1. Design Parameters
| DESIGN PARAMETER | EXAMPLE VALUE |
|---|---|
| Input Voltage Range | 0 V to Vsup-1.5 V |
| Supply Voltage | 4.5 V to VCC maximum |
| Logic Supply Voltage | 0 V to VCC maximum |
| Output Current (RPULLUP) | 1 µA to 4 mA |
| Input Overdrive Voltage | 100 mV |
| Reference Voltage | 2.5 V |
| Load Capacitance (CL) | 15 pF |
8.2.2 Detailed Design Procedure
When using the LM139-MIL in a general comparator application, determine the following:
- Input voltage range
- Minimum overdrive voltage
- Output and drive current
- Response time
8.2.2.1 Input Voltage Range
When choosing the input voltage range, the input common-mode voltage range (VICR) must be taken in to account. If temperature operation is above or below 25°C the VICR can range from 0 V to VCC– 2 V. This limits the input voltage range to as high as VCC– 2 V and as low as 0 V. Operation outside of this range can yield incorrect comparisons.
The following list describes the outcomes of some input voltage situations.
- When both IN– and IN+ are both within the common-mode range:
- If IN– is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking current
- If IN– is lower than IN+ and the offset voltage, the output is high impedance and the output transistor is not conducting
- When IN– is higher than common mode and IN+ is within common mode, the output is low and the output transistor is sinking current
- When IN+ is higher than common mode and IN– is within common mode, the output is high impedance and the output transistor is not conducting
- When IN– and IN+ are both higher than common mode, the output is low and the output transistor is sinking current
8.2.2.2 Minimum Overdrive Voltage
Overdrive voltage is the differential voltage produced between the positive and negative inputs of the comparator over the offset voltage (VIO). To make an accurate comparison, the overdrive voltage (VOD) must be higher than the input offset voltage (VIO). Overdrive voltage can also determine the response time of the comparator, with the response time decreasing with increasing overdrive. Figure 8 and Figure 9 show positive and negative response times with respect to overdrive voltage.
8.2.2.3 Output and Drive Current
Output current is determined by the load and pullup resistance and logic and pullup voltage. The output current produces a low-level output voltage (VOL) from the comparator, where VOL is proportional to the output current.
The output current can also effect the transient response.
8.2.2.4 Response Time
Response time is a function of input over-drive. See the Typical Characteristics graphs for typical response times. The rise and fall times can be determined by the load capacitance (CL), load/pull-up resistance (RPULLUP) and equivalent collector-emitter resistance (RCE).
- The rise time (τR) is approximately τR~ RPULLUP × CL
- The fall time (τF) is approximately τF ~ RCE × CL
- RCE can be determined by taking the slope of Figure 3 in its linear region at the desired temperature, or by dividing the VOL by IOUT
8.2.3 Application Curves
Figure 8 and Figure 9 were generated with scope probe parasitic capacitance of 50 pF.
| VCC = 5 V | VLogic = 5 V | RPULLUP = 5.1 kΩ |
(Positive Transition)
| VCC = 5 V | VLogic = 5 V | RPULLUP = 5.1 kΩ |
(Negative Transition)