ISL78229 Datasheet, PDF (28/71 Pages) Intersil Corporation – 2-Phase Boost Controller with Drivers

ISL78229
I_L1
180°
t
I_L2
t
I_L1+I_L2
t
FIGURE 61. PHASE NODE AND INDUCTOR-CURRENT WAVEFORMS
FOR 2-PHASE CONVERTER
To understand the reduction of the ripple current amplitude in the
multiphase circuit, examine Equation 4 representing an individual
phase’s peak-to-peak inductor current.
In Equation 4, V_IN and V_OUT are the input and the output voltages
respectively, L is the single-phase inductor value and f_SW is the
switching frequency.
I_{PPCH =} ^_---V----^O_-L----^U_-f-S--^T_--W---^–_{----VV----OI--}^N_--U--^_--T--V----^I_--^N_--
(EQ. 4)
The input capacitors conduct the ripple component of the
inductor current. In the case of a 2-phase boost converters, the
capacitor current is the sum of the ripple currents from each of
the individual phases. Use Equation 5 to calculate the
peak-to-peak ripple of the total input current which goes through
the input capacitors, where K_P-P can be found in Figure 62 under
specific duty cycle.
I_PPALL= K_P-P  I_PPCH
(EQ. 5)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.4 5 0.5 0.55 0.6 0.65 0 .7 0.75 0.8 0.85 0.9
DUTY CYCLE
FIGURE 62. K_P-P vs DUTY CYCLE
CURRENT SHARING BETWEEN PHASES
The peak current mode control inherently has current sharing
capability. As shown in Figure 3 on page 7, the current sense
ramp V_RAMPx of each phase are compared to the same error
amplifier’s output at the COMP pin by the PWM comparators to
turn off LGx when V_RAMPx reaches COMP. Thus, the V_RAMPx
peaks are controlled to be the same for each phase. V_RAMPx is
the sum of instantaneous inductor current sense ramp and the
compensating slope. Since the compensating slopes are the
same for both phases, the inductor peak current of each phase is
controlled to be the same.
The same mechanism applies to the case when multiple
ISL78229s are configured in parallel for multiphase boost
converter. Basically, the COMP pin of each ISL78229 are tied
together for each phase’s current sense ramp peak to be
compared with the same COMP voltage (V_RAMPx = COMP),
meaning the inductor peak current of all the phases are
controlled to be the same. The “4-Phase Operation” section
describes how to configure two ISL78229 in parallel for a
4-phase interleaved boost converter.
4-PHASE OPERATION
Two ISL78229s can be used in parallel to achieve interleaved
4-phase operation. Figure 63 shows the recommended
configuration. The CLKOUT from the master IC drives FSYNC of
the slave IC to synchronize the switching frequencies. This
achieves a 90° phase shift for the 4 phases switching, and the
respective COMP, FB, SS, EN and IMON pins of the two ICs are
connected.
CLKOUT is 90°out-of-phase with the rising edge of LG1.
therefore, the two phases of the second IC are interleaved with
the two phases of the first IC.
CLKOUT
COMP
MASTER IC ^FB
ISL78229 _SS
IMON
EN
FSYNC
COMP
FB _{SLAVE IC}
SS ^ISL78229
IMON
EN
FIGURE 63. CONFIGURATIONS FOR DUAL IC 4-PHASE OPERATION
When using PMBus™ functions for the two ISL78229 operating
in parallel, the telemetry functions as reading register
information from the ISL78229 will work fine. For example, the
host can read via PMBus™ for the VIN, FB, IMON, NTC voltages,
fault status and all other registers. The host only reads the
information and does not change the operating conditions.
However, when using WRITE commands to either control an
ISL78229 action (like OPERATION ON/OFF), or configure the
fault protection response or thresholds, the designer should
carefully evaluate the scenarios of the two ICs operation in
parallel. For example, it's recommended to configure both of the
ICs to have the same fault thresholds settings. Otherwise, one of
the IC's thresholds will not be effective. If any fault protection
occurs (Latch-off or Hiccup), since the SS pins are connected
together, the two ICs' PWM switching will be shut off. Generally,
it's suggested to set the fault response to Hiccup mode. When
fault condition is gone, the two ICs can always restart to normal
operations.
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FN8656.3
February 12, 2016