Datasheet MAX4172 (Maxim) - 7
| Manufacturer | Maxim |
| Description | Low-Cost, Precision, High-Side Current-Sense Amplifier |
| Pages / Page | 9 / 7 — Table 1. Suggested Component Values. FULL-SCALE. CURRENT-SENSE. OUTPUT. … |
| Revision | 4 |
| File Format / Size | PDF / 1.6 Mb |
| Document Language | English |
Table 1. Suggested Component Values. FULL-SCALE. CURRENT-SENSE. OUTPUT. LOAD CURRENT. RESISTOR,. RESISTOR, ROUT. SCALE FACTOR,. (A)
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link to page 7 MAX4172 Low-Cost, Precision, High-Side Current-Sense Amplifier
Table 1. Suggested Component Values FULL-SCALE CURRENT-SENSE OUTPUT FULL-SCALE LOAD CURRENT RESISTOR, RESISTOR, ROUT OUTPUT SCALE FACTOR, (A) RSENSE (mΩ) (kΩ) VOLTAGE, V VOUT/ISENSE (V/A) OUT (V)
0.1 1000 3.48 3.48 34.8 1 100 3.48 3.48 3.48 5 20 3.48 3.48 0.696 10 10 3.48 3.48 .348
Sense Resistor, RSENSE
Choose RSENSE based on the following criteria: INPUT R LOAD/BATTERY SENSE ●
Voltage Loss:
A high RSENSE value causes the O.3 in. COPPER O.1 in. COPPER O.3 in. COPPER power-source voltage to degrade through IR loss. For minimal voltage loss, use the lowest RSENSE value. ●
Accuracy:
A high RSENSE value allows lower currents VSENSE to be measured more accurately. This is because offsets become less significant when the sense VSUPPLY 1 voltage is larger. For best performance, select R 8 SENSE RS+ V+ 3V TO 32V to provide approximately 100mV of sense voltage for 2
MAX4172
RS- the full-scale current in each application. 6 ●
Efficiency and Power Dissipation:
At high current OUT levels, the I2R losses in RSENSE can be significant. GND 5 R Take this into consideration when choosing the resistor OUT value and its power dissipation (wattage) rating. Also, the sense resistor’s value might drift if it is allowed to heat up excessively. Figure 2. MAX4172 Connections Showing Use of PC Board ●
Inductance:
Keep inductance low if ISENSE has a large high-frequency component. Wire-wound resis- tors have the highest inductance, while metal film is
Current-Sense Adjustment
somewhat better. Low-inductance metal-film resistors
(Resistor Range, Output Adjust)
are also available. Instead of being spiral wrapped Choose R around a core, as in metal-film or wirewound resistors, OUT after selecting RSENSE. Choose ROUT to obtain the full-scale voltage you require, given the they are a straight band of metal and are available in full-scale I values under 1Ω. OUT determined by RSENSE. OUT’s high impedance permits using R ●
Cost:
If the cost of R OUT values up to 200kΩ with SENSE is an issue, you might minimal error. OUT’s load impedance (e.g., the input of an want to use an alternative solution, as shown in Figure op amp or ADC) must be much greater than R 2. This solution uses the PCB traces to create a sense OUT (e.g., 100 x R resistor. Because of the inaccuracies of the copper OUT) to avoid degrading measurement accuracy. resistor, the full-scale current value must be adjusted with
High-Current Measurement
a potentiometer. Also, copper’s resistance temperature The MAX4172 can achieve high-current measurements by coefficient is fairly high (approximately 0.4%/°C). using low-value sense resistors, which can be paralleled In Figure 2, assume that the load current to be measured to further increase the current-sense limit. As an alternative, is 10A, and that you have determined a 0.3-inchwide, PCB traces can be adjusted over a wide range. 2-ounce copper to be appropriate. The resistivity of 0.1-inch-wide, 2-ounce (70μm thickness) copper is 30mΩ/ ft. For 10A, you might want RSENSE = 5mΩ for a 50mV drop at full scale. This resistor requires about 2 inches of 0.1-inch-wide copper trace. www.maximintegrated.com Maxim Integrated │ 7
Table 1. Suggested Component Values FULL-SCALE CURRENT-SENSE OUTPUT FULL-SCALE LOAD CURRENT RESISTOR, RESISTOR, ROUT OUTPUT SCALE FACTOR, (A) RSENSE (mΩ) (kΩ) VOLTAGE, V VOUT/ISENSE (V/A) OUT (V)
0.1 1000 3.48 3.48 34.8 1 100 3.48 3.48 3.48 5 20 3.48 3.48 0.696 10 10 3.48 3.48 .348
Sense Resistor, RSENSE
Choose RSENSE based on the following criteria: INPUT R LOAD/BATTERY SENSE ●
Voltage Loss:
A high RSENSE value causes the O.3 in. COPPER O.1 in. COPPER O.3 in. COPPER power-source voltage to degrade through IR loss. For minimal voltage loss, use the lowest RSENSE value. ●
Accuracy:
A high RSENSE value allows lower currents VSENSE to be measured more accurately. This is because offsets become less significant when the sense VSUPPLY 1 voltage is larger. For best performance, select R 8 SENSE RS+ V+ 3V TO 32V to provide approximately 100mV of sense voltage for 2
MAX4172
RS- the full-scale current in each application. 6 ●
Efficiency and Power Dissipation:
At high current OUT levels, the I2R losses in RSENSE can be significant. GND 5 R Take this into consideration when choosing the resistor OUT value and its power dissipation (wattage) rating. Also, the sense resistor’s value might drift if it is allowed to heat up excessively. Figure 2. MAX4172 Connections Showing Use of PC Board ●
Inductance:
Keep inductance low if ISENSE has a large high-frequency component. Wire-wound resis- tors have the highest inductance, while metal film is
Current-Sense Adjustment
somewhat better. Low-inductance metal-film resistors
(Resistor Range, Output Adjust)
are also available. Instead of being spiral wrapped Choose R around a core, as in metal-film or wirewound resistors, OUT after selecting RSENSE. Choose ROUT to obtain the full-scale voltage you require, given the they are a straight band of metal and are available in full-scale I values under 1Ω. OUT determined by RSENSE. OUT’s high impedance permits using R ●
Cost:
If the cost of R OUT values up to 200kΩ with SENSE is an issue, you might minimal error. OUT’s load impedance (e.g., the input of an want to use an alternative solution, as shown in Figure op amp or ADC) must be much greater than R 2. This solution uses the PCB traces to create a sense OUT (e.g., 100 x R resistor. Because of the inaccuracies of the copper OUT) to avoid degrading measurement accuracy. resistor, the full-scale current value must be adjusted with
High-Current Measurement
a potentiometer. Also, copper’s resistance temperature The MAX4172 can achieve high-current measurements by coefficient is fairly high (approximately 0.4%/°C). using low-value sense resistors, which can be paralleled In Figure 2, assume that the load current to be measured to further increase the current-sense limit. As an alternative, is 10A, and that you have determined a 0.3-inchwide, PCB traces can be adjusted over a wide range. 2-ounce copper to be appropriate. The resistivity of 0.1-inch-wide, 2-ounce (70μm thickness) copper is 30mΩ/ ft. For 10A, you might want RSENSE = 5mΩ for a 50mV drop at full scale. This resistor requires about 2 inches of 0.1-inch-wide copper trace. www.maximintegrated.com Maxim Integrated │ 7
