ISL62882_14 Datasheet, PDF (17/42 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs and GPUs

ISL62882, ISL62882B
ISEN2
INTERNAL
TO IC
ISEN1
V2p
PHASE2
Rs
Cs Rs
Rs
Rs
Cs
PHASE1
V1p
L2
Rdcr2 _{V2n Rpcb2}
IL2
VO
L1
Rdcr1
Rpcb1
V1n
IL1
FIGURE 14. DIFFERENTIAL-SENSING CURRENT BALANCING
CIRCUIT
Sometimes, it is difficult to implement symmetrical layout. For
the circuit Figure 13 shows, asymmetric layout causes different
R_pcb1 and R_pcb2 thus current imbalance. Figure 14 shows a
differential-sensing current balancing circuit recommended for
ISL62882. The current sensing traces should be routed to the
inductor pads so they only pick up the inductor DCR voltage. Each
ISEN pin sees the average voltage of two sources: its own phase
inductor phase-node pad, and the other phase inductor output
side pad. Equations 7 and 8 give the ISEN pin voltages:
V_ISEN1 = V_1p + V_2n
(EQ. 7)
V_ISEN2 = V_2p + V_1n
(EQ. 8)
The ISL62882 will make V_ISEN1 = V_ISEN2. So there are:
V_1p + V_2n = V_2p + V_1n
(EQ. 9)
Rewriting Equation 9 gives:
V_1p – V_1n = V_2p – V_2n
(EQ. 10)
Therefore:
R_dcr1 × I_L1 = R_dcr2 × I_L2
(EQ. 11)
Current balancing (I_L1 = I_L2) will be achieved when there is
R_dcr1 = R_dcr2. R_pcb1 and R_pcb2 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 ISL62882
evaluation board with load transient of 15A/50A 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 a 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.
REP RATE = 10kHz
REP RATE = 25kHz
REP RATE = 50kHz
REP RATE = 100kHz
REP RATE = 200kHz
FIGURE 15. ISL62882 EVALUATION BOARD CURRENT BALANCING
DURING DYNAMIC OPERATION.
Ch1: IL1, Ch2: I_Ioad, Ch3: IL2
17
FN6890.4
June 21, 2011