ISL6557A Datasheet, PDF (17/19 Pages) Intersil Corporation – Multi-Phase PWM Controller for Core-Voltage Regulation

ISL6557A
Application on page 3). Figure 14 and Equation 26 are
0.3
provided to assist in the selecting the correct value for RT.
1000
0.2
100
10
10
100
1000
SWITCHING FREQUENCY (KHZ)
FIGURE 14. RT VS SWITCHING FREQUENCY
10000
RT = 10^{[11.09 – 1.13log (fS)]}
(EQ. 26)
Input Capacitor Selection
The input capacitors are responsible for sourcing the ac
component of the input current flowing into the upper
MOSFETs. Their rms current capacity must be sufficient to
handle the ac component of the current drawn by the upper
MOSFETs which is related to duty cycle and the number of
active phases.
Figures 15, 16 and 17 can be used to determine the input-
capacitor rms current as of duty cycle, maximum sustained
output current (I_O), and the ratio of the combined peak-to-
peak inductor current (I_L,PP as defined in Equation 1) to the
maximum sustained load current, I_O. Figure 18 is provided
as a reference to demonstrate the dramatic reductions in
input-capacitor rms current upon the implementation of the
multiphase topology.
0.1
I_L,PP = 0
I_L,PP = 0.5 I_O
I_L,PP = 0.75 I_O
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE ( V_IN / V_O )
FIGURE 15. NORMALIZED INPUT-CAPACITOR RMS CURRENT
VS DUTY CYCLE FOR 2-PHASE CONVERTER
0.3 _{IL,PP = 0}
I_L,PP = 0.25 I_O
I_L,PP = 0.5 I_O
I_L,PP = 0.75 I_O
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE ( V_IN / V_O )
FIGURE 16. NORMALIZED INPUT-CAPACITOR RMS CURRENT
VS DUTY CYCLE FOR 3-PHASE CONVERTER
17