Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
ISL97650 Datasheet(PDF) 14 Page - Renesas Technology Corp |
|
ISL97650 Datasheet(HTML) 14 Page - Renesas Technology Corp |
14 / 20 page ISL97650 FN9198 Rev.4.00 Page 14 of 20 April 17, 2009 Rectifier Diode (Buck Converter) A Schottky diode is recommended due to fast recovery and low forward voltage. The reverse voltage rating should be higher than the maximum input voltage. The peak current rating is 2A, and the average current should be as shown in Equation 15: Where Io is the output current of buck converter. Table 8 shows some recommended diodes. Output Capacitor (Buck Converter) Four 10µF or two 22µF ceramic capacitors are recommended for this part. The overshoot and undershoot will be reduced with more capacitance, but the recovery time will be longer. PI Loop Compensation (Buck Converter) The buck converter of ISL97650 can be compensated by a RC network connected from CM2 pin to ground. C9 = 4.7nF and R2 = 2k RC network is used in the demo board. The larger value resistor can lower the transient overshoot, however, at the expense of stability of the loop. The stability can be optimized in a similar manner to that described in the section “PI Loop Compensation (Boost Converter)” on page 12. Bootstrap Capacitor (C16) This capacitor is used to provide the supply to the high driver circuitry for the buck MOSFET. The bootstrap supply is formed by an internal diode and capacitor combination. A 1µF is recommended for ISL97650. A low value capacitor can lead to overcharging and in turn damage the part. If the load is too light, the on-time of the low side diode may be insufficient to replenish the bootstrap capacitor voltage. In this case, if VIN-VBUCK < 1.5V, the internal MOSFET pull-up device may be unable to turn-on until VLOGIC falls. Hence, there is a minimum load requirement in this case. The minimum load can be adjusted by the feedback resistors to FBL. The bootstrap capacitor can only be charged when the higher side MOSFET is off. If the load is too light which can not make the on time of the low side diode be sufficient to replenish the boot strap capacitor, the MOSFET can’t turn on. Hence there is minimum load requirement to charge the bootstrap capacitor properly. Charge Pump Controllers (VON and VOFF) The ISL97650 includes 2 independent charge pumps (see charge pump block and connection diagram, Figure 17). The negative charge pump inverts the VSUP voltage and provides a regulated negative output voltage. The positive charge pump doubles or triples the VSUP voltage and provides a regulated positive output voltage. The regulation of both the negative and positive charge pumps is generated by internal comparator that senses the output voltage and compares it with the internal reference. The pumps use pulse width modulation to adjust the pump period, depending on the load present. The pumps can provide 30mA for VOFF and 20mA for VON. Positive Charge Pump Design Consideration The positive charge pump integrates all the diodes (D1, D2 and D3 shown in the “Block Diagram” on page 9) required for x2 (VSUP doubler) and x3 (VSUP Tripler) modes of operation. During the chip start-up sequence, the mode of operation is automatically detected when the charge pump is enabled. With both C7 and C8 present, the x3 mode of operation is detected. With C7 present, C8 open and with C1+ shorted to C2+, the x2 mode of operation will be detected. Due to the internal switches to VSUP (M1, M2 and M3), POUT is independent of the voltage on VSUP until the charge pump is enabled. This is important for TFT applications where the negative charge pump output voltage (VOFF) and AVDD supplies need to be established before POUT. The maximum POUT charge pump current can be estimated from the following equations assuming a 50% switching duty: Note: VDIODE (2 • IMAX) is the on-chip diode voltage as a function of IMAX and VDIODE (40mA) < 0.7V. TABLE 8. BUCK RECTIFIER DIODE RECOMMENDATION DIODE VR/IAVG RATING PACKAGE VENDOR PMEG2020EJ 20V/2A SOD323F Philips Semiconductors SS22 20V/2A SMB Fairchild Semiconductor TABLE 9. BUCK OUTPUT CAPACITOR RECOMMENDATION CAPACITOR SIZE VENDOR PART NUMBER 10µF/6.3V 0805 TDK C2012X5R0J106M 10µF/6.3V 0805 Murata GRM21BR60J106K 22µF/6.3V 1210 TDK C3216X5R0J226M 100µF/6.3V 1206 Murata GRM31CR60J107M Iavg 1D – *I o = (EQ. 15) IMAX 2x min of 50mA or 2V SUP 2 – VDIODE 2IMAX VV ON – 22 rONH rONL + ---------------------------------------------------------------------------------------------------------------------- 0.95A IMAX 3x min of 50mA or 3V SUP 3 – VDIODE 2IMAX VV ON – 23 rONH 2r ONL + ---------------------------------------------------------------------------------------------------------------------- 0.95V (EQ. 16) |
Número de pieza similar - ISL97650 |
|
Descripción similar - ISL97650 |
|
|
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 |