Datasheet LT4351 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | MOSFET Diode-OR Controller |
| Pages / Page | 20 / 10 — APPLICATIONS INFORMATION. Boost Regulator. Figure 6. Table 1. Recommended … |
| File Format / Size | PDF / 346 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Boost Regulator. Figure 6. Table 1. Recommended Inductors. PART NUMBER. IND (µH). DCR (mΩ). VENDOR
Model Line for this Datasheet
Text Version of Document
LT4351
APPLICATIONS INFORMATION
In that case, the resistor values are set by:
Boost Regulator
UV R3 = HYST The boost regulator will start working as soon as VIN is IUVHYST greater than 0.85V. The regulator will supply all the cur- UV rent for the gate drive amplifier. While the amplifier itself V FAULT UV – • V OV OV requires only about 3mA, larger current pulses are required R2 = FAULT • R3 when charging the MOSFET gate. The reservoir capacitor UVFAULT – VUV on VDD will provide this current (Figure 6). V R1= OV • UVFAULT ( ) •R3 VIN OVFAULT • UVFAULT – VUV Hysteresis helps prevent erratic behavior due to the noise L1 on V LT4351 IN. Two of the most common noise sources are: VIN D1 SW dipping when the MOSFETs first turn on and draw down V QSW DD the voltage on the VIN capacitors, and the boost regulator D2 CDD switch turning on and drawing current from the VIN ca- GND pacitors. Use low ESR capacitors for VIN and OUT filtering. 4351 F06 Note that because the UV pin uses current hysteresis,
Figure 6
placing a capacitor on UV to ground to filter noise will reduce the effective hysteresis. Filtering can be achieved The regulator performance is relatively insensitive to the by splitting the R2 resistor, as shown in Figure 4. inductor value. The inductor value does control the fre- To defeat undervoltage fault detection, the UV pin should quency of operation. A 4.7µH inductor is recommended be tied higher than 0.33V. UV can be tied to VIN provided for VIN voltages less than 10V and 10µH for VIN voltages VIN < 9V. Overvoltage fault detection can be defeated by greater than 10V. Several inductors that work well with grounding the OV pin. Do not exceed VIN. the LT4351 are listed in Table 1. Many different sizes and shapes are available. Consult each manufacturer for more detailed information and for their entire selection of related INPUT OV UV REFERRED REFERRED REFERRED parts. The switching frequency for the boost regulator is OVERVOLTAGE FAULT: around 1MHz so ferrite core inductors should be used GATE LOW V to obtain the best efficiency. The inductor must handle a OVERVOLTAGE FILTERED FAULT UV = 0.33V OVFAULT VUV = 0.3V peak current of 0.7A minimum and have a DC resistance GATE CONTROLLED V BY V OV > 0.3V V of 0.5Ω or less. Shielded inductors are recommended to UV < 0.3V IN – VOUT UVFAULT + UVHYST reduce the noise due to inductive switching. UNDERVOLTAGE HYSTERESIS UVFAULT VOV = 0.3V UNDERVOLTAGE FAULT:
Table 1. Recommended Inductors
GATE LOW 4351 F05
PART NUMBER IND (µH) DCR (mΩ) VENDOR
LPS3314-472ML 4.7 175 Coilcraft LPS4012-103ML 10 350 847-639-6400
Figure 5. Graphical Representation of the UV and OV Functions
www.coilcraft.com 744029004 4.7 200 Würth Elektronik
External Shutdown
744042100 10 150 www.we-online.com SD3112-4R7-R 4.7 246 Coiltronics To externally turn off the MOSFETs, such as to disable the SD3118-100-R 10 295 www.coiltronics.com supply, use an open-collector transistor pulling down on the UV pin. Note this will not turn off the boost regulator which will continue to operate. 4351fd 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts
APPLICATIONS INFORMATION
In that case, the resistor values are set by:
Boost Regulator
UV R3 = HYST The boost regulator will start working as soon as VIN is IUVHYST greater than 0.85V. The regulator will supply all the cur- UV rent for the gate drive amplifier. While the amplifier itself V FAULT UV – • V OV OV requires only about 3mA, larger current pulses are required R2 = FAULT • R3 when charging the MOSFET gate. The reservoir capacitor UVFAULT – VUV on VDD will provide this current (Figure 6). V R1= OV • UVFAULT ( ) •R3 VIN OVFAULT • UVFAULT – VUV Hysteresis helps prevent erratic behavior due to the noise L1 on V LT4351 IN. Two of the most common noise sources are: VIN D1 SW dipping when the MOSFETs first turn on and draw down V QSW DD the voltage on the VIN capacitors, and the boost regulator D2 CDD switch turning on and drawing current from the VIN ca- GND pacitors. Use low ESR capacitors for VIN and OUT filtering. 4351 F06 Note that because the UV pin uses current hysteresis,
Figure 6
placing a capacitor on UV to ground to filter noise will reduce the effective hysteresis. Filtering can be achieved The regulator performance is relatively insensitive to the by splitting the R2 resistor, as shown in Figure 4. inductor value. The inductor value does control the fre- To defeat undervoltage fault detection, the UV pin should quency of operation. A 4.7µH inductor is recommended be tied higher than 0.33V. UV can be tied to VIN provided for VIN voltages less than 10V and 10µH for VIN voltages VIN < 9V. Overvoltage fault detection can be defeated by greater than 10V. Several inductors that work well with grounding the OV pin. Do not exceed VIN. the LT4351 are listed in Table 1. Many different sizes and shapes are available. Consult each manufacturer for more detailed information and for their entire selection of related INPUT OV UV REFERRED REFERRED REFERRED parts. The switching frequency for the boost regulator is OVERVOLTAGE FAULT: around 1MHz so ferrite core inductors should be used GATE LOW V to obtain the best efficiency. The inductor must handle a OVERVOLTAGE FILTERED FAULT UV = 0.33V OVFAULT VUV = 0.3V peak current of 0.7A minimum and have a DC resistance GATE CONTROLLED V BY V OV > 0.3V V of 0.5Ω or less. Shielded inductors are recommended to UV < 0.3V IN – VOUT UVFAULT + UVHYST reduce the noise due to inductive switching. UNDERVOLTAGE HYSTERESIS UVFAULT VOV = 0.3V UNDERVOLTAGE FAULT:
Table 1. Recommended Inductors
GATE LOW 4351 F05
PART NUMBER IND (µH) DCR (mΩ) VENDOR
LPS3314-472ML 4.7 175 Coilcraft LPS4012-103ML 10 350 847-639-6400
Figure 5. Graphical Representation of the UV and OV Functions
www.coilcraft.com 744029004 4.7 200 Würth Elektronik
External Shutdown
744042100 10 150 www.we-online.com SD3112-4R7-R 4.7 246 Coiltronics To externally turn off the MOSFETs, such as to disable the SD3118-100-R 10 295 www.coiltronics.com supply, use an open-collector transistor pulling down on the UV pin. Note this will not turn off the boost regulator which will continue to operate. 4351fd 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts
