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LTM4633 Folha de dados(PDF) 16 Page - Linear Technology |
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LTM4633 Folha de dados(HTML) 16 Page - Linear Technology |
16 / 32 page LTM4633 16 4633f For more information www.linear.com/LTM4633 applicaTions inForMaTion Stability Compensation TheLTM4633hasalreadybeeninternallycompensatedfor all output voltages. Table 5 is provided for most applica- tion requirements with verified stability. LTpowerCAD is available for other control loop optimization. Run Enable The RUN 1, 2, 3 pins have an enable threshold of 1.4V maximum, typically 1.3V with 175mV of hysteresis. They control the turn-on of their respective channel. There is a 10k resistor on each pin to ground. The RUN pins can be pulled up to VIN for 5V operation, or a resistor can be placed on the pins and connected to VIN for higher than 5V input. This resistor can be set along with the onboard 10k resistor such that an undervoltage lockout (UVLO) level can be programmed to shut down a particular regulator channel if VIN falls below a set value. Use the equation: R = 10k UVLO–1.3V ( ) 1.3V where R is the resistor from the RUN pin to VIN to set the UVLO trip point. For example, if the UVLO point is to be 6.25V while operating at 12V input: R = 10k 6.25V –1.3V ( ) 1.3V ≈ 38.3k See the Typical Application circuits in Figure 17. The RUN pins must not go above 6V maximum voltage. The RUN pins have to be pulled up to enable the regulators. SW Pins The SW pins are generally used for testing purposes by monitoring the pin of interest. The SW pins can also be used to dampen out switch node ringing caused by LC parasiticsintheswitchedcurrentpath.UsuallyaseriesR-C combination is used called a snubber circuit. The resistor will dampen the resonance and the capacitor is chosen to only affect the high frequency ringing across the resistor. If the stray inductance or capacitance can be measured or approximated then a somewhat analytical technique can be used to select the snubber values. The inductance is usually easier to predict. It combines the PowerPath™ board inductance in combination with the MOSFET inter- connect inductance. First, the SW pin can be monitored using a wide band- width scope with a high frequency scope probe. The ring frequency can be measured for its value. The impedance, Z, can be calculated: Z(L) = 2π • f • L where f is the resonant frequency of the ring, and L is the total parasitic inductance in the switch path. If a resistor is selected that is equal to Z, then the ringing should be dampened. The snubber capacitor value is then chosen so that its impedance is equal to the resistor at the ring frequency: Z(C) = 1 2 π • f •C These values are a good place to start with. Modification to these components should be made to attenuate the ring- ing without lowering the regulator’s conversion efficiency. INTVCC and EXTVCC The LTM4633 has an onboard linear regulator fed by CNTL_PWR which delivers a roughly 5V output at INTVCC to power the internal controller and MOSFET drivers for all three regulator channels. CNTL_PWR requires a voltage between 4.7V to 16V. Apply a 4.7µF ceramic capacitor between INTVCC and ground for decoupling. If the volt- age supplied to CNTL_PWR is ≤ 5.5V, connect INTVCC to CNTL_PWR. Otherwise, INTVCC should be left floating. To eliminate power loss in the onboard linear regulator and improve efficiency connect a supply from 4.7V to 6V at EXTVCC. Biasing EXTVCC will reduce the power loss in the internal LDO by (VCNTL_PWR – 5V) • 70mA. If EXTVCC is used add a 1µF ceramic capacitor to ground at EXTVCC and |
Nº de peça semelhante - LTM4633 |
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Descrição semelhante - LTM4633 |
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