ISL62883C Просмотр технического описания (PDF) - Intersil

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ISL62883C

Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs and GPUs

Intersil 

ISL62883C

Current balancing (IL1 = IL2 = IL3) will be achieved

when there is Rdcr1 = Rdcr2 = Rdcr3. Rpcb1, Rpcb2 and

Rpcb3 will not have any effect.

Since the slave ripple capacitor voltages mimic the

inductor currents, R3™ modulator can naturally achieve

excellent current balancing during steady state and

dynamic operations. Figure 15 shows current balancing

performance of the ISL62883C evaluation board with load

transient of 12A/51A at different rep rates. The inductor

currents follow the load current dynamic change with the

output capacitors supplying the difference. The inductor

currents can track the load current well at low rep rate,

but cannot keep up when the rep rate gets into the

hundred-kHz range, where it’s out of the control loop

bandwidth. The controller achieves excellent current

balancing in all cases installed.

CCM Switcing Frequency

The Rfset resistor between the COMP and the VW pins

sets the sets the VW windows size, therefore sets the

switching frequency. When the ISL62883C is in

continuous conduction mode (CCM), the switching

frequency is not absolutely constant due to the nature of

the R3™ modulator. As explained in the Multiphase R3™

Modulator section, the effective switching frequency will

increase during load insertion and will decrease during

load release to achieve fast response. On the other hand,

the switching frequency is relatively constant at steady

state. Variation is expected when the power stage

condition, such as input voltage, output voltage, load,

etc. changes. The variation is usually less than 15% and

doesn’t have any significant effect on output voltage

ripple magnitude. Equation 17 gives an estimate of the

frequency-setting resistor Rfset value. 8kΩ Rfset gives

approximately 300kHz switching frequency. Lower

resistance gives higher switching frequency.

Rfset(kΩ) = (Period(μs) – 0.29) × 2.65

(EQ. 17)

REP RATE = 10kHz

REP RATE = 25kHz

REP RATE = 50kHz

REP RATE = 100kHz

REP RATE = 200kHz

FIGURE 15. ISL62883 EVALUATION BOARD CURRENT

BALANCING DURING DYNAMIC

OPERATION. CH1: IL1, CH2: ILOAD, CH3:

IL2, CH4: IL3

19

FN7557.1

March 18, 2010

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