Datasheet LTC3672B-2 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in 2mm × 2mm DFN |
| Pages / Page | 12 / 8 — OPERATION. Switch Slew-Rate Control. LOW DROPOUT LINEAR REGULATORS … |
| File Format / Size | PDF / 161 Kb |
| Document Language | English |
OPERATION. Switch Slew-Rate Control. LOW DROPOUT LINEAR REGULATORS (LDOs). LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT
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LTC3672B-2
OPERATION Switch Slew-Rate Control LOW DROPOUT LINEAR REGULATORS (LDOs)
The buck regulator contains new patent pending circuitry The LTC3672B-2 contains two 150mA fi xed-output LDO to limit the slew rate of the switch node (SW pin). This regulators. LDO1 takes power from the VIN1 pin and new circuitry is designed to transition the switch node regulates a 2.8V output at the LDO1 pin. LDO2 takes over a period of a couple nanoseconds, signifi cantly power straight from VIN and regulates a 1.8V output at reducing radiated EMI and conducted supply noise while the LDO2 pin. maintaining high effi ciency. For stability, each LDO output must be bypassed to ground with a minimum 1μF ceramic capacitor.
LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT
An undervoltage lockout (UVLO) circuit shuts down the LTC3672B-2 when VIN drops below about 1.7V.
APPLICATIONS INFORMATION BUCK REGULATOR INDUCTOR SELECTION
Different core materials and shapes will change the size/cur- rent and price/current relationship of an inductor. Toroid Many different sizes and shapes of inductors are avail- or shielded pot cores in ferrite or Permalloy™ materials able from numerous manufacturers. Choosing the right are small and don’t radiate much energy, but generally inductor from such a large selection of devices can be cost more than powdered iron core inductors with similar overwhelming, but following a few basic guidelines will electrical characteristics. Inductors that are very thin or make the selection process much simpler. have a very small volume typically have much higher core The buck regulator is designed to work with inductors in and DCR losses, and will not give the best effi ciency. The the range of 2.2μH to 10μH. A 4.7μH inductor is a good choice of which style inductor to use often depends more starting point. Larger value inductors reduce ripple cur- on the price vs size, performance, and any radiated EMI rent, which improves output ripple voltage. Lower value requirements than on what the buck regulator needs to inductors result in higher ripple current and improved operate. transient response time. To maximize effi ciency, choose Table 1 shows several inductors that work well with the an inductor with a low DC resistance. Choose an inductor buck regulator. These inductors offer a good compromise with a DC current rating at least 1.5 times larger than the in current rating, DCR and physical size. Consult each maximum load current to ensure that the inductor does not manufacturer for detailed information on their entire saturate during normal operation. If output short-circuit selection of inductors. is a possible condition, the inductor should be rated to handle the maximum peak current specifi ed for the step- down converters. 3672b2fa 8
OPERATION Switch Slew-Rate Control LOW DROPOUT LINEAR REGULATORS (LDOs)
The buck regulator contains new patent pending circuitry The LTC3672B-2 contains two 150mA fi xed-output LDO to limit the slew rate of the switch node (SW pin). This regulators. LDO1 takes power from the VIN1 pin and new circuitry is designed to transition the switch node regulates a 2.8V output at the LDO1 pin. LDO2 takes over a period of a couple nanoseconds, signifi cantly power straight from VIN and regulates a 1.8V output at reducing radiated EMI and conducted supply noise while the LDO2 pin. maintaining high effi ciency. For stability, each LDO output must be bypassed to ground with a minimum 1μF ceramic capacitor.
LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT
An undervoltage lockout (UVLO) circuit shuts down the LTC3672B-2 when VIN drops below about 1.7V.
APPLICATIONS INFORMATION BUCK REGULATOR INDUCTOR SELECTION
Different core materials and shapes will change the size/cur- rent and price/current relationship of an inductor. Toroid Many different sizes and shapes of inductors are avail- or shielded pot cores in ferrite or Permalloy™ materials able from numerous manufacturers. Choosing the right are small and don’t radiate much energy, but generally inductor from such a large selection of devices can be cost more than powdered iron core inductors with similar overwhelming, but following a few basic guidelines will electrical characteristics. Inductors that are very thin or make the selection process much simpler. have a very small volume typically have much higher core The buck regulator is designed to work with inductors in and DCR losses, and will not give the best effi ciency. The the range of 2.2μH to 10μH. A 4.7μH inductor is a good choice of which style inductor to use often depends more starting point. Larger value inductors reduce ripple cur- on the price vs size, performance, and any radiated EMI rent, which improves output ripple voltage. Lower value requirements than on what the buck regulator needs to inductors result in higher ripple current and improved operate. transient response time. To maximize effi ciency, choose Table 1 shows several inductors that work well with the an inductor with a low DC resistance. Choose an inductor buck regulator. These inductors offer a good compromise with a DC current rating at least 1.5 times larger than the in current rating, DCR and physical size. Consult each maximum load current to ensure that the inductor does not manufacturer for detailed information on their entire saturate during normal operation. If output short-circuit selection of inductors. is a possible condition, the inductor should be rated to handle the maximum peak current specifi ed for the step- down converters. 3672b2fa 8
