ISL62883_14 Datasheet, PDF (16/37 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs

ISL62883, ISL62883B
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.
REP RATE = 10kHz
REP RATE = 25kHz
REP RATE = 50kHz
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 12
shows current balancing performance of the ISL62883
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.
CCM Switching 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 ISL62883 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 = 100kHz
REP RATE = 200kHz
Phase Count Configurations
The ISL62883 can be configured for 3-, 2- or 1-phase operation.
For 2-phase configuration, tie the PWM3 pin to 5V. Phase-1 and
Phase-2 PWM pulses are 180° out-of-phase. In this
configuration, the ISEN3/FB2 pin (pin 9) serves the FB2 function.
For 1-phase configuration, tie the PWM3 and ISEN2 pins to 5V. In
this configuration, only Phase-1 is active. The ISEN3/FB2, ISEN2,
and ISEN1 pins are not used because there is no need for either
current balancing or FB2 function.
FIGURE 12. ISL62883 EVALUATION BOARD CURRENT BALANCING
DURING DYNAMIC OPERATION. CH1: IL1, CH2: I_LOAD,
CH3: IL2, CH4: IL3
16
FN6891.4
June 21, 2011