ISL6567_07 Datasheet, PDF (9/26 Pages) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

ISL6567
COMP
R2
C1
FB
R1
VDIFF
REFERENCE
OSCILLATOR
PWM
Σ
CIRCUIT
PWM
Σ
CIRCUIT
Σ
AVERAGE
Σ
VSEN
RGND
ISL6567
V_IN
UGATE1
HALF-BRIDGE
DRIVE
HALF-BRIDGE
DRIVE
CURRENT
SENSE
CURRENT
SENSE
PHASE1
LGATE1
L1
R_ISEN1
ISEN1
V_IN
L2
UGATE2
PHASE2
LGATE2
ISEN2
R_ISEN2
V_OUT
C_OUT
FIGURE 2. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6567 VOLTAGE AND CURRENT CONTROL LOOPS
Operation
Figure 2 shows a simplified diagram of the voltage regulation
and current loops. The voltage loop is used to precisely
regulate the output voltage, while the current feedback is
used to balance the output currents, I_L1 and I_L2, of the two
power channels.
VOLTAGE LOOP
Feedback from the output voltage is fed via the on-board
differential amplifier and applied via resistor R1 to the
inverting input of the Error Amplifier. The signal generated by
the error amplifier is summed up with the current correction
error signal and applied to the positive inputs of the PWM
circuit comparators. Out-of-phase sawtooth signals are
applied to the two PWM comparators inverting inputs.
Increasing error amplifier voltage results in increased duty
cycle. This increased duty cycle signal is passed to the
output drivers with no phase reversal to drive the external
MOSFETs. Increased duty cycle, translating to increased
ON-time for the upper MOSFET transistor, results in
increased output voltage, compensating for the low output
voltage which lead to the increase in the error signal in the
first place.
CURRENT LOOP
The current control loop is only used to finely adjust the
individual channel duty cycle, in order to balance the current
carried by each phase. The information used for this control
is the voltage that is developed across r_DS(ON) of each lower
MOSFET, while they are conducting. A resistor converts and
scales the voltage across each MOSFET to a current that is
applied to the current sensing circuits within the ISL6567.
Output from these sensing circuits is averaged and used to
compute a current error signal. Each PWM channel receives
a current signal proportional to the difference between the
average sensed current and the individual channel current.
When a PWM channel’s current is greater than the average
current, the signal applied via the summing correction circuit
to the PWM comparator reduces the output pulse width (duty
cycle) of the comparator to compensate for the detected
above average current in the respective channel.
MULTI-PHASE POWER CONVERSION
Multi-phase power conversion provides a cost-effective
power solution when load currents are no longer easily
supported by single-phase converters. Although its greater
complexity presents additional technical challenges, the
multi-phase approach offers advantages with improved
response time, superior ripple cancellation, and thermal
distribution.
9
FN9243.2
March 20, 2007