Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
LTM4634 Datasheet(PDF) 13 Page - Linear Technology |
|
LTM4634 Datasheet(HTML) 13 Page - Linear Technology |
13 / 32 page LTM4634 13 4634f For more information www.linear.com/LTM4634 applicaTions inForMaTion frequencies optimize efficiency, eliminate minimum on- timeissuesforlessthan1Voutput,andcontroltheinductor ripple currents over the input and output voltage ranges. 24Vinputapplicationsthatconverttooutputvoltagesequal to 5V (VOUT1,2) and up to 12V (VOUT3) will be required to set the LTM4634 switching frequency to 750kHz. This is required to maintain less than 60% inductor ripple current at the higher output voltages. The 750kHz requirement for these higher output conversions from 24V will limit outputvoltagesonotherchannelstobenolowerthan1.5V due to minimum on-time considerations. There is a way around this issue by taking one of these outputs, either 5V or 12V, and using it as the source for the 0.8V to 1.5V output. An example circuit is shown in Figure 26. 5V and 12V input conversions on all three channels can be oper- ated at lower frequencies across the output ranges so that minimum on-time is not an issue at low output voltages. The minimum on-time equation on the next page can be used to verify that no switching frequency is violating this parameter. The equations for checking IRIPPLE %: VIN – VOUT ( )VOUT L •IRIPPLE • VIN =FREQ, IRIPPLE CH#MaxLoad =IRIPPLE% This verifies that the operating frequencies are selected to limitinductorripplecurrentstobebelow60%ofmaximum load, where FREQ is selected frequency in Hertz, IRIPPLE and maximum load current in amps, and L is inductance in Henrys. Ch1, Ch2 L = 1.5µH, and Ch3 L = 3.3µH. Maxi- mum load current IOUT1,2 = 5A, and IOUT3 = 4A, therefore IRIPPLE should try to stay below 2.5A for Ch1, Ch2, and 2A for Ch3, except for 12V output. The efficiency curves will show the recommended optimal operating frequency for the different conversions A DC voltage should be applied to the FREQ/PLLLPF pin to set the operating frequency when clock synchroniza- tion is not used. Figure 2 shows the frequency selection as a function of the applied DC voltage. This can be done with a voltage divider from the INTVCC (5V) pin to SGND. A 10k resistor can be selected as the bottom resistor. The top resistor, RFREQ, can be determined by using equation: RFREQ = 5V •10k FREQV –10k where FREQV is the voltage at the FREQ/PLLLPF pin in Figure 2 that corresponds to a particular frequency. See Figure 25 for an example. FREQ/PLLLPF PIN VOLTAGE (V) 0 0.5 1 1.5 2 4634 F02 2.5 300 400 500 800 700 200 600 Figure 2. Relationship Between Oscillator Frequency and Voltage at the FREQ/PLLLPF Pin Parallel Channel Operation For outputs that demand more than 5A of load current, the LTM4634 device can parallel VOUT1 and VOUT2 to sup- ply 10A of load current. The two channels will operate at 120° of phase shift. The input RMS ripple current can be calculated using Equation 1. For example, 12V to 1.2V at 10A equates to duty cycle D = 0.1. ICIN(RMS) = 10A 0.85 • 0.1• 1– 0.1 ( ) ICIN(RMS)=3.5ARMS,use2×22µF16VX5RorX7Rceramic capacitors rated at 2ARMS each. The LTM4634 regulators are inherently current mode controlled devices, so the paralleling of VOUT1 and VOUT2 channels will have good current sharing. This will balance the thermals in the design. Tie the COMP, VFB, TK/SS and RUN pins together for these two channels to share the current evenly. Figure 24 shows a schematic of the parallel design. Minimum On-Time Minimum on-time, tON, is the smallest time duration that any of the three regulator channels is capable of turning on the top MOSFET. It is determined by internal timing delays, and the gate charge required to turn on the top MOSFET. |
Número de pieza similar - LTM4634 |
|
Descripción similar - LTM4634 |
|
|
Enlace URL |
Política de Privacidad |
ALLDATASHEET.ES |
¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |