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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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IC-DC датащи(PDF) 14 Page - IC-Haus GmbH |
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IC-DC датащи(HTML) 14 Page - IC-Haus GmbH |
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14 / 19 page  iC-DC 2-CHANNEL BUCK/BOOST DC/DC CONVERTER Rev B1, Page 14/19 REVERSE POLARITY PROTECTION A protective switch inserted between supply VB and pin VBR protects the entire system against reverse polarity. This can also be used to implement an Autarky function (see AUTARKY FUNCTION). By connecting VB to VBR the reverse polarity protection circuit can be bridged to improve the current carrying capacity and the overall efficiency, especially if low supply voltages are used (Figure 5). ENABLE R2 R3 R4 OUTPUT SWITCH 2 PROTECT. SUPPLY VCC2: SWITCH 1 VOLTAGE MONITOR LIN.-REG.2 CONTROL THERMAL SHUTDOWN BUCK SUPPLY SUPPLY LIN.-REG.1 MONITORING REFERENCE BIAS BOOST SWITCHING REGULATOR 3.3V/2.5V/R3:R4 R1 OSCILLATOR iC-DC ERROR DETECT. AUTARKY DETECT. REVERSE INTERNAL CONFIGURATION VOLTAGE 2 5V/3.3V/R1:R2 VCC1: 1 22μH LVBH CVH2 CVH1 3.3μF 3.3μF CVH 1μF CVCC2 CVCC1 1μF 3.3μF 2 1 1 1μF CVB & 2 20k RREF RREF VCC1,VCC2 TEST V1OK V2OK VCC2 POE2 TOK VBROK VH1 VCC1 VCC2 GND VBR VBL VHL VH GNDA VB CFG1 CFG2 ENV1 ENV2 NAUT 4...36V 1.5...5.5V 1.5...5.5V VH2 POE1 VCC1 LVBH 22μH CVCC2 1μF 1μF CVCC1 CVH2 3.3μF 3.3μF CVH1 CVH 3.3μF CVB 1μF RREF 20k & Figure 5: Protection against reverse polarity deacti- vated, bridges VB to VBR The reverse polarity protection switch is current lim- ited to the maximum mean current consumption of the system (Electrical Characteristics 104). A capacitor (CVBR) must be connected to pin VBR if higher coil cut-off currents are to be supplied. This capacitor should have a value of at least 1 µF at a supply voltage of VB = 24 V (Figure 6). With very small supply voltages the value must be greater in or- der to cater for the higher power consumption during startup. The voltage at VBR must no longer drop below the lower shutdown threshold (Electrical Characteristics 202) to ensure safe converter startup. A capacitor of approx. 10 µF should thus be selected for CVBR at a supply voltage of VB = 4 V (Figure 7). VOLTAGE ENABLE R2 R3 R4 OUTPUT SWITCH 2 5V/3.3V/R1:R2 VCC1: VCC2: SWITCH 1 VOLTAGE MONITOR PROTECT. SUPPLY THERMAL SHUTDOWN BUCK SUPPLY SUPPLY LIN.-REG.1 LIN.-REG.2 CONTROL MONITORING REFERENCE BIAS BOOST SWITCHING REGULATOR 3.3V/2.5V/R3:R4 R1 OSCILLATOR iC-DC ERROR DETECT. AUTARKY DETECT. REVERSE INTERNAL CONFIGURATION 20k RREF 1 22μH LVBH CVBR 1μF 1μF CVB CVH1 3.3μF 3.3μF CVH 1μF CVCC2 CVCC1 1μF 3.3μF CVH2 2 2 1 & 2 RREF VCC1,VCC2 TEST V1OK V2OK VCC2 POE2 TOK VBROK VH1 VCC1 VCC2 GND 24V 1 VBR VBL VHL VH GNDA VB CFG1 CFG2 ENV1 ENV2 NAUT 1.5...5.5V 1.5...5.5V VH2 POE1 VCC1 LVBH 22μH RREF 20k CVCC2 1μF 1μF CVCC1 CVH2 3.3μF 3.3μF CVH1 CVH 3.3μF CVB 1μF 1μF CVBR & Figure 6: Protection against reverse polarity active, CVBR for VB = 24 V LIN.-REG.2 CONTROL MONITORING REFERENCE BIAS BOOST SWITCHING REGULATOR 3.3V/2.5V/R3:R4 R1 OSCILLATOR iC-DC ERROR DETECT. AUTARKY DETECT. REVERSE INTERNAL CONFIGURATION VOLTAGE ENABLE R2 R3 R4 OUTPUT SWITCH 2 5V/3.3V/R1:R2 VCC1: VCC2: SWITCH 1 VOLTAGE MONITOR PROTECT. SUPPLY THERMAL SHUTDOWN BUCK SUPPLY SUPPLY LIN.-REG.1 & 1 2 1 CVH2 3.3μF 3.3μF CVH1 CVH 3.3μF CVCC2 1μF 1μF CVCC1 2 2 1 LVBH 22μH CVB 1μF 10μF CVBR RREF 20k RREF VCC1,VCC2 TEST V1OK V2OK VCC2 POE2 TOK VBROK VH1 VCC1 VCC2 GND 4V VBR VBL VHL VH GNDA VB CFG1 CFG2 ENV1 ENV2 NAUT 1.5...5.5V 1.5...5.5V VH2 POE1 VCC1 & 1μF CVCC2 CVCC1 1μF 3.3μF CVH2 CVH1 3.3μF 3.3μF CVH 1μF CVB CVBR 10μF 22μH LVBH 20k RREF Figure 7: Protection against reverse polarity active, CVBR for VB = 4 V It is possible to use the protective switch at pin VBR to provide further circuitry with protection against re- verse polarity (Figure 9, Page 17). Here, it must noted that the current carrying capacity of the reverse polarity protection (VBR) is limited on startup. As the device powers itself from VBR, the load at VBR must not be too high as otherwise converter operation cannot be initiated. The current carrying capacity on startup can be approximately described by Equation 3: I(VBR) = V(VB) ∗ − 1mA V (3) |
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