SLCS007 Data sheet

SLCS007K September 1973 – March 2017 LM111 , LM211 , LM311

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9 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.

9.1 Application Information

A typical LMx11 application compares a single signal to a reference or two signals against each other. 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 LMx11 optimal for level shifting to a higher or lower voltage.

9.2 Typical Application

Figure 13. Zero-Crossing Detector

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 1 as the input parameters.

Table 1. Design Parameters

PARAMETER		MIN	MAX	UNIT
V_IN	Input voltage range	–15	13	V
V_CC+	Positive supply voltage		15	V
V_CC–	Negative supply voltage	–15
I_OUT	Output current		20	mA

9.2.2 Detailed Design Procedure

When using LMx11 in a general comparator application, determine the following:

Input voltage range
Minimum overdrive voltage
Output and drive current
Response time

9.2.2.1 Input Voltage Range

When choosing the input voltage range, consider the input common mode voltage range (V_ICR). 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 undefined

9.2.2.2 Minimum Overdrive Voltage

Overdrive voltage is the differential voltage produced between the positive and negative inputs of the comparator over the offset voltage (V_IO). To make an accurate comparison the Overdrive voltage (V_OD) must be higher than the input offset voltage (V_IO). Overdrive voltage can also determine the response time of the comparator, with the response time decreasing with increasing overdrive. Figure 14 and Figure 15 show positive and negative response times with respect to overdrive voltage.

9.2.2.3 Output and Drive Current

Output current is determined by the pullup resistance and pullup voltage. The output current produces a output low voltage (V_OL) from the comparator, in which V_OL is proportional to the output current. Use Figure 5 to determine V_OL based on the output current.

The output current can also effect the transient response.

9.2.2.4 Response Time

The load capacitance (C_L), pullup resistance (R_PULLUP), and equivalent collector-emitter resistance (R_CE) levels determine the transient response. Equation 1 approximates the positive response time. Equation 2 approximates the negative response time. R_CE can be determine by taking the slope of Figure 5 in the linear region at the desired temperature, or by Equation 3.

Equation 1. LM111 LM211 LM311 q_tp_slcs006.gif