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LTC3827-1 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3827-1 Datasheet(HTML) 10 Page - Linear Technology |
10 / 16 page LTC4365 10 4365f Figure 4 shows the timing associated with the UV pin. Once a UV fault propagates through the UV comparator (tFAULT), the FAULT output is asserted low and a 50mA current sink discharges the GATE pin. As VOUT falls, the GATE pin tracks VOUT. APPLICATIONS INFORMATION Figure 5 shows the timing associated with the OV pin. Once an OV fault propagates through the OV comparator (tFAULT), the FAULT output is asserted low and a 50mA current sink discharges the GATE pin. As VOUT falls, the GATE pin tracks VOUT. Procedure for Selecting UV/OV External Resistor Values The following 3-step procedure helps select the resistor values for the resistive divider of Figure 3. This procedure minimizes UV and OV offset errors caused by leakage currents at the respective pins. 1. Choose maximum tolerable offset at the UV pin, VOS(UV). Divide by the worst case leakage current at the UV pin, IUV (10nA). Set the sum of R1 + R2 equal to VOS(UV) divided by 10nA. Note that due to the presence of R3, the actual offset at UV will be slightly lower: R1 +R2= V OS(UV) I UV 2. Select the desired VIN UV trip threshold, UVTH. Find the value of R3: R3 = 2• V OS(UV) I UV •UV TH – 0.5V () 3. Select the desired VIN OV trip threshold, OVTH. Find the values of R1 and R2: R1= VOS(UV) IUV +R3 2• OVTH R2 = V OS(UV) I UV –R1 The example of Figure 3 uses standard 1% resistor values. The following parameters were selected: VOS(UV) = 3mV IUV = 10nA UVTH = 3.5V OVTH = 18V 4365 F04 FAULT GATE tFAULT tGATE(FAST) VUV VUV + VUVHYST tFAULT tRECOVERY EXTERNAL N-CHANNEL MOSFET TURNS OFF UV 4365 F05 FAULT GATE tFAULT tGATE(FAST) VOV VOV – VOVHYST tFAULT tRECOVERY EXTERNAL N-CHANNEL MOSFET TURNS OFF OV Figure 4. UV Timing (OV < (VOV – VOVHYST), SHDN > 1.2V) Figure 5. OV Timing (UV > (VUV + VUVHYST), SHDN > 1.2V) When both the UV and OV faults are removed, the external MOSFET is not immediately turned on. The input supply must remain within the user selected power good window for at least 36ms (tRECOVERY) before the load is again connected to the supply. This recovery timeout period filters noise (including line noise) at the input supply and prevents chattering of power at the load. |
Similar Part No. - LTC3827-1 |
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Similar Description - LTC3827-1 |
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