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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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MIC5021 датащи(PDF) 14 Page - Microchip Technology |
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MIC5021 датащи(HTML) 14 Page - Microchip Technology |
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14 / 24 page  MIC5021 DS20005677B-page 14 2016 - 2021 Microchip Technology Inc. and its subsidiaries. External Schottky diodes are also recommended (see D2 and D3 in Figure 6-9). The external diodes clamp negative transients better than the internal diodes because their larger size minimizes the forward voltage drop at higher currents. FIGURE 6-9: Protection from Inductive Kick. 6.9.4 HIGH-SIDE SENSING Sensing the current on the high side of the MOSFET isolates the sense pins from the inductive spike. FIGURE 6-10: High-Side Sensing. 6.10 Lamp Driver Application Incandescent lamps have a high inrush current (low resistance) when turned on. The MIC5021 can perform a “soft start” by pulsing the MOSFET (overcurrent con- dition) until the filament is warm and its current decreases (resistance increases). The sense resistor value is selected so the voltage drop across the sense resistor decreases below the sense threshold (50 mV) as the filament becomes warm. The FET is no longer pulsed and the lamp turns completely on. A lamp may not fully turn on if the filament does not heat up adequately. Changing the duty cycle, sense resistor, or both to match the filament characteristics can correct the problem. Soft start can be demonstrated using a #1157 dual fila- ment automotive lamp. The value of RS shown in Figure 6-11 allows for soft start of the higher-resistance filament (measures approx. 2.1Ω cold or 21Ω hot). FIGURE 6-11: Lamp Driver with Current Sensing. 6.11 Remote Overcurrent Limiting Reset In circuit breaker applications where the MIC5021 maintains an off condition after an overcurrent condi- tion is sensed, the CT pin can be used to reset the MIC5021. FIGURE 6-12: Remote Control Circuit. Switching Q1 on pulls CT low which keeps the MIC5021 gate output off when an overcurrent is sensed. Switch- ing Q1 off causes CT to appear open. The MIC5021 retries in about 20 µs and continues to retry until the overcurrent condition is removed. For demonstration purposes, a 680Ω load resistor and 3Ω sense resistor will produce an overcurrent condition when the load’s supply (V+) is approximately 12V or greater. V DD INPUT C T GND V BOOST GATE SENSE- SENSE+ TTL INPUT INDUCTIVE LOAD N-CHANNEL POWER MOSFET +12V TO +36V MIC5021 1 2 3 4 8 7 6 5 10μF 2.7 nF RSENSE 1.0k 330Ω R2 D2 11DQ03 D3 11DQ03 D1 R1 VDD INPUT C T GND V BOOST GATE SENSE- SENSE+ TTL INPUT WIREWOUND RESISTOR (3Ω) N-CHANNEL POWER MOSFET (IRFZ44) +12V TO +20V RSENSE (< 0.01Ω) (+12V) MIC5021 1 2 3 4 8 7 6 5 10μF 0.01 μF VDD INPUT C T GND V BOOST GATE SENSE- SENSE+ TTL INPUT RSENSE (0.041Ω) N-CHANNEL POWER MOSFET (IRF540) V+ MIC5021 1 2 3 4 8 7 6 5 10μF 0.01 μF INCANDESCENT LAMP (#1157) (+12V) "( )" VALUES APPLY TO DEMO CIRCUIT. SEE TEXT. VDD INPUT C T GND VBOOST GATE SENSE- SENSE+ TTL INPUT RSENSE N-CHANNEL POWER MOSFET +12V TO +20V MIC5021 1 2 3 4 8 7 6 5 10μF 0.01 μF LOAD 74HC04 (EXAMPLE) 2N3904 Q1 10k TO 100k RETRY (H) MAINTAINED (L) |
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