ISL6219 Datasheet, PDF (16/17 Pages) Intersil Corporation – Microprocessor CORE Voltage Regulator Precision Multi-Phase BUCK PWM Controller for Mobile Applications

ISL6219
page 3). Figure 13 and Equation 23 are provided to assist in
the selecting the correct value for RT.
RT = 10^{[11.09 – 1.13log (fS)]}
(EQ. 23)
1000
0.3 _{IPP = 0}
I_PP = 0.25 I_O
0.2
I_PP = 0.5 I_O
I_PP = 0.75 I_O
100
10
10
100
1000
SWITCHING FREQUENCY (KHZ)
FIGURE 13. RT VS SWITCHING FREQUENCY
10000
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 14 and 15 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) to I_O. Figure 16 is provided as a
reference to demonstrate the dramatic reductions in input-
capacitor rms current upon the implementation of the
multiphase topology.
0.3
0.1
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 3-PHASE
0.6
0.4
0.2
I_PP = 0
I_PP = 0.5 I_O
I_PP = 0.75 I_O
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 SINGLE-PHASE
CONVERTER
0.2
0.1
I_PP = 0
I_PP = 0.5 I_O
I_PP = 0.75 I_O
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE (V_O /V_IN )
FIGURE 14. NORMALIZED INPUT-CAPACITOR RMS
CURRENT VS DUTY CYCLE FOR 2-PHASE
16