ISL62883C Datasheet, PDF (19/43 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs and GPUs

ISL62883C
Current balancing (I_L1 = I_L2 = I_L3) will be achieved
when there is R_dcr1 = R_dcr2 = R_dcr3. R_pcb1, R_pcb2 and
R_pcb3 will not have any effect.
Since the slave ripple capacitor voltages mimic the
inductor currents, R³â„¢ 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 R_fset 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 R³â„¢ modulator. As explained in the Multiphase R³â„¢
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 R_fset value. 8kΩ R_fset gives
approximately 300kHz switching frequency. Lower
resistance gives higher switching frequency.
R_fset(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: I_LOAD, CH3:
IL2, CH4: IL3
19
FN7557.1
March 18, 2010