ISL78226 Datasheet, PDF (34/94 Pages) Intersil Corporation – Cycle-by-cycle peak current limiting

ISL78226
Operation Description
The ISL78226 is an automotive grade (AEC Q100 Grade-1)
6-phase synchronous bidirectional controller. This controller
enables the configuration of a multiphase bidirectional power
converter system between a 12V battery and a 48V battery with
external FET drivers, N-channel power MOSFETs, and a few
additional passive components. Typically, a converter system
with a power rating of up to 3kW can be realized with the
combination of driver ICs and adequately rated power MOSFETs.
The device also supports parallel connection of up to four
ISL78226 devices to realize up to 12-phase operation.
The ISL78226 also offers selectable phase dropping/adding and
diode emulation/forced PWM switching mode for enhanced
light-load efficiency.
The ISL78226 employs a constant frequency Peak Current Mode
Control (PCMC) scheme, which offers the benefits of input
voltage feed-forward regulation, a simpler loop compensator
compared to voltage mode control, and inherent current sharing
capability.
In addition to cycle-by-cycle current limiting, the ISL78226 has a
dedicated average Constant Current (CC) control loop which
enables accurate control of the average output current for Buck
mode operation and average input current for Boost mode
operation without shutdown. It enables the user to fully utilize the
system’s power device capability by accurately controlling
constant input power.
The ISL78226 provides several system diagnostics and fault
detection features including input/output overvoltage warning
and protection, input/output undervoltage warning and
protection, overcurrent warning and protection, and device status
monitoring. The status of the device operation and faults are
communicated with host microcontroller in the system via a
PMBus-compliant digital interface. Also, with this digital
interface, the ISL78226 provides access to useful system control
parameters through internal registers.
The ISL78226 also implements an internal LDO for stable device
operation, an MCULDO for external MCU or other system power
supply, and a Flyback controller to generate driver power supply
and pre-regulated supply voltage for the device. These features
support the minimization of effort and components in designing
the required power supplies in the system.
Details of the functions are described in the following sections.
Bidirectional Power Conversion
Due to the increase of electrical power demand in a vehicle and
strong motivation for environmental and energy-saving
requirements, a 48V battery system is considered a solution for
next-generation vehicles in addition to the conventional 12V
battery system. In this system, a multiphase bidirectional power
converter between the batteries (a Buck converter from 48V to
12V, or a Boost converter from 12V to 48V) is required to
supplement the power of each battery system. The ISL78226
enables the multiphase bidirectional power converter with one
controller.
Multiphase Interleaving Control
For an n-phase, interleaved, multiphase converter, the PWM
switching of each phase is distributed evenly with 360/n phase
shift. The total combined current ripples at the input and output
are reduced where smaller input and output capacitors can be
used. In addition, it is beneficial to have a smaller equivalent
inductor for a faster loop design. Also in some applications,
especially in a high-current case, multiphase makes it possible to
use a smaller inductor for each phase rather than one big
inductor (single-phase), which is sometimes more costly or
unavailable on the market at the high-current rating. Smaller size
inductors also help to achieve low profile design.
The ISL78226 is a controller for multiphase, interleaved
converter which enables selection of 6, 4, 3, and 2-phase
operations. In 6-, 4-, 3- and 2-phase operations, each phase is
operating with 60°, 90°, 120°, and 180° phase shift,
respectively. This means that each PWM pulse is triggered 1/6,
1/4, 1/3, and 1/2, respectively, of a cycle after the start of the
PWM pulse of the previous phase. Figure 30 illustrates the
interleaving effect on input ripple current in 6-phase operation in
Buck mode. The AC component of the 6-phase currents (I_L1, I_L2,
I_L3, I_L4, I_L5, I_L6) are interleaving each other and the combined AC
current ripple (I_Ltotal) at input are reduced. Equivalently, the
frequency of the AC inductor ripple at input is six times that of
the switching frequency per phase.
40.00
80.00
35.00
75.00
30.00
70.00
25.00
65.00
20.00
60.00
15.00
55.00
10.00
50.00
5.00
45.00
0.00
0
40.00
20
40
60
80
100
120
140
160
180
200
IL1
IL2
IL3
IL4
IL5
IL6
IOUT
FIGURE 30. TOTAL AND PER PHASE INDUCTOR RIPPLE CURRENT
Oscillator and Clock Synchronization
The switching frequency is determined by the selection of the
frequency-setting resistor, R_FSYNC, connected from FSYNC pin to
GND. Equation 1 is provided to assist in selecting the correct
resistor value.
R_FSYNC
=
4.6
x10⁹
x


f^--_S^--1--_W^----
–
9.2
X
10^–8_
(EQ. 1)
Where f_SW is the switching frequency of each phase.
Figure 31 shows the relationship between Rfs and switching
frequency.
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November 7, 2016