参数资料
| 型号： | ISL78220ANEZ-T |
| 厂商： | Intersil |
| 文件页数： | 12/22页 |
| 文件大小： | 0K |
| 描述： | IC PWM CONTROLLER |
| 标准包装： | 1,000 |
| 系列： | * |
ISL78220
Operation Description
( V OUT – V IN ) V IN (EQ. 1)
Multiphase Power Conversion
The technical challenges associated with producing a single-
phase converter, which is both cost-effective and thermally viable
for high power applications have forced a change to the
cost-saving approach of multiphase solution. The ISL78220
controller helps reduce the complexity of implementation by
integrating vital functions and requiring minimal output
components.
Interleaving
The switching of each channel in a multiphase converter is timed
to be symmetrically out-of-phase with each of the other channels.
Take a 3-phase converter for example, each channel switches
1/3 cycle after the previous channel and 1/3 cycle before the
following channel. As a result, the three-phase converter has a
combined ripple frequency three times greater than the ripple
frequency of any one phase. In addition, the peak-to-peak
amplitude of the combined inductor current is reduced in
proportion to the number of phases (Equations 1 and 2). The
increased ripple frequency and the lower ripple amplitude mean
that the designer can use less per-channel inductance and lower
total input and output capacitance for any performance
specification.
Figure 13 illustrates the multiplicative effect on input ripple
current. The three channel currents (I L1 , I L2 , and I L3 ) combine to
form the AC ripple current and the DC input current. The ripple
component has three times the ripple frequency of each
individual channel current. Each PWM pulse is triggered 1/3 of a
cycle after the start of the PWM pulse of the previous phase.
To understand the reduction of the ripple current amplitude in the
multiphase circuit, examine the equation representing an
individual channel’s peak-to-peak inductor current.
In Equation 1, V IN and V OUT are the input and the output voltages
respectively, L is the single-channel inductor value, and f S is the
switching frequency.
I P-P = ---------------------------------------------
L f S V OUT
The input capacitors conduct the ripple component of the
inductor current. In the case of multiphase converters, the
capacitor current is the sum of the ripple currents from each of
the individual channels. Compare Equation 1 to the expression for
the peak-to-peak current after the summation of N symmetrically
phase-shifted inductor currents in Equation 2. Peak-to-peak
ripple current decreases by an amount proportional to the
number of channels. Reducing the inductor ripple current allows
the designer to use fewer or less costly input capacitors.
IL1 + IL2 + IL3
IL3
PWM3
IL2
PWM2
IL1
PWM1
TIME
FIGURE 13. PWM AND INDUCTOR-CURRENT WAVEFORMS FOR
3-PHASE CONVERTER
PWM Operations
The timing of each channel is set by the total number of active
channels. The default channel setting for the ISL78220 is 6, and
the switching cycle is defined as the time between PWM pulse
initiation signals of each channel. The cycle time of the pulse
initiation signal is the inversion of the switching frequency set by
the resistor between the FS pin and ground. The PWM signals
command the MOSFET drivers to turn on/off the channel
MOSFETs. Normal operation assumes PWM_INV is tied to GND
and inverting MOSFET drivers are used.
In the default 6-phase operation, the PWM2 pulse starts 1/6 of a
cycle after PWM1, the PWM3 pulse starts 1/6 of a cycle after
PWM2, the PWM4 pulse starts 1/6 of a cycle after PWM3, the
PWM5 pulse starts 1/6 of a cycle after PWM4, and the PWM6
pulse starts 1/6 of a cycle after PWM5.
Phase Selection
The ISL78220 can work in 1, 2, 3, 4, 5 or 6-phase configuration.
Connecting the PWM5 or PWM6 to VCC selects 4-phase
operation and the pulse times are spaced in 1/4 cycle
increments. Connecting the PWM4 to VCC selects 3-phase
operation and the pulse times are spaced in 1/3 cycle
increments. Connecting the PWM3 to VCC selects 2-phase
operation and the pulse times are spaced in 1/2 cycle
increments. For the unused ISENxN and ISENxP, a 1k ? resistor is
recommended to connect ISENxN and ISENxP, and connect
ISENxN to VIN.
Modes of Operations
The different mode of operations will be determined by the
voltage combinations of the MODE pin and the PWM_TRI pin.
I C ( P-P ) = ---------------------------------------------------
( V OUT – N V IN ) V IN
L f S V OUT
12
(EQ. 2)
If automatic phase adding/dropping function is not needed, the
MODE pin should be tied to VCC (Logic HIGH). If higher light load
efficiency is preferred, phase adding/dropping function could be
implemented by connecting the MODE pin through a resistor to
GND. A 5μA reference current will flow out of MODE pin to
generate corresponding V MODE . V MODE is used to compare with
V IOUT to determine the phase adding/dropping level.
FN7688.3
December 24, 2013
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