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ISL6528 Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL6528 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 13 page 9 FN9038.4 March 9, 2006 by placing them nearby. Position both the ceramic and bulk input capacitors as close to the upper MOSFET drain as possible. Position the output inductor and output capacitors between the upper MOSFET and lower diode and the load. The critical small signal components include any bypass capacitors, feedback components, and compensation components. Position the bypass capacitor, CBP, close to the VCC pin with a via directly to the ground plane. Place the PWM converter compensation components close to the FB and COMP pins. The feedback resistors for both regulators should also be located as close as possible to the relevant FB pin with vias tied straight to the ground plane as required. Component Selection Guidelines Output Capacitor Selection Output capacitors are required to filter the output and supply the load transient current. The filtering requirements are a function of switching frequency and output current ripple. The load transient requirements are a function of the transient load current slew rate (di/dt) and magnitude. These requirements are generally met with a mix of capacitors and careful layout. PWM REGULATOR OUTPUT CAPACITORS Modern digital ICs can produce high transient load slew rates. High frequency capacitors initially supply the transient current and slow the load rate-of-change seen by the bulk capacitors. The bulk filter capacitor selection is generally determined by the effective series resistance (ESR) and voltage rating requirements rather than actual capacitance requirements. High frequency decoupling capacitors should be placed as close to the power pins of the load as physically possible. Be careful not to add inductance in the circuit board wiring that could cancel the usefulness of these low inductance components. Consult with the manufacturer of the load on specific decoupling requirements. Specialized low-ESR capacitors intended for switching- regulator applications are recommended for the bulk capacitors. The bulk capacitor’s ESR determines the output ripple voltage and the initial voltage drop following a high slew-rate transient edge. Aluminum electrolytic, tantalum, and special polymer capacitor ESR values are related to the case size with lower ESR available in larger case sizes. However, the equivalent series inductance (ESL) of these capacitors increases with case size and can reduce the usefulness of the capacitor to high slew-rate transient loading. Unfortunately, ESL is not a specified parameter. Work with your capacitor supplier and measure the capacitor’s impedance with frequency to select a suitable component. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. LINEAR REGULATOR OUTPUT CAPACITORS The output capacitors for the linear regulator provide dynamic load current. The linear controller uses dominant pole compensation integrated into the error amplifier and is relatively insensitive to output capacitor selection. Output capacitors should be selected for transient load regulation. PWM Output Inductor Selection The PWM converter requires an output inductor. The output inductor is selected to meet the output voltage ripple requirements and sets the converter response time to a load transient. The inductor value determines the converter’s ripple current and the ripple voltage is also a function of the ripple current. The ripple voltage and current are approximated by the following equations: Increasing the value of inductance reduces the output ripple current and voltage ripple. However, increasing the VOUT1 +5 VCC ISLAND ON POWER PLANE LAYER ISLAND ON CIRCUIT PLANE LAYER LOUT COUT1 CIN +3.3 VIN KEY COMP ISL6528 UGATE R4 R2 CBP FB DRIVE2 GND VCC D1 FIGURE 7. PRINTED CIRCUIT BOARD POWER PLANES AND ISLANDS R1 Q2 VOUT2 BOOT FB2 C2 VIA CONNECTION TO GROUND PLANE COUT2 Q1 CBOOT +3.3 VIN R5 R6 PHASE D2 R3 C3 C1 ∆I VIN VOUT – FS L × -------------------------------- VOUT VIN ---------------- × = VOUT ∆ I ∆ ESR × = (EQ. 11) (EQ. 12) ISL6528 |
Similar Part No. - ISL6528_06 |
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Similar Description - ISL6528_06 |
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