ISL6315_07 Datasheet, PDF (7/20 Pages) Intersil Corporation – Two-Phase Multiphase Buck PWM Controller with Integrated MOSFET Drivers

ISL6315
Operation
The ISL6315 employs simple voltage-mode control. Figure 1
shows a simplified diagram of the voltage regulation and
current balance loops. Voltage feedback is used to precisely
regulate the output voltage, while current feedback tightly
controls the individual channel currents, I_L1 and I_L2, and
trips the OC protection, if so necessary.
VOLTAGE LOOP
Feedback from the output voltage is applied via resistor R1
to the inverting input of the Error Amplifier. This signal can
drive the Error Amplifier output either high or low, depending
upon the output voltage. Low output voltage makes the
amplifier output move towards a higher output voltage level.
Amplifier output voltage is applied to the positive inputs of
the PWM Circuit comparators via the channel current
correction summing networks. Out-of-phase sawtooth
signals are applied to the two PWM comparators inverting
inputs. Increasing Error Amplifier voltage results in increased
Comparator output duty cycle. This increased duty cycle
signal is passed through the output drivers with no phase
reversal to drive the external upper MOSFETs. Increased
duty cycle or ON time for the upper MOSFET transistors
results in increased output voltage to compensate for the low
output voltage sensed.
CHANNEL BALANCE CURRENT LOOP
The current balance control loop works in a similar fashion to
the voltage control loop, but with current control information
applied individually to each channel’s PWM circuit. The
information used for this control is the voltage that is
developed across the r_DS(ON) of each lower MOSFET, while
they are conducting. A single resistor converts and scales
the voltage across the MOSFETs to a current that is applied
to the Current Sensing circuit within the ISL6315. Output
from these sensing circuits is applied to the current
averaging circuit. Each PWM channel receives the
difference current signal from the summing circuit that
compares the average sensed current to the individual
channel current. When a power channel’s current is greater
than the average current, the signal applied via the summing
Correction circuit to the Comparator, reduces the output
pulse width of the Comparator to compensate for the
detected “above average” current in that channel.
MULTIPHASE POWER CONVERSION
Multiphase 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
multiphase approach offers cost-saving advantages with
improved response time, superior ripple cancellation, and
thermal distribution.
COMP
R2
C2
FB
R1
DAC
&
REFERENCE
Σ
OSCILLATOR
PWM
CIRCUIT
ERROR
AMP
PWM
Σ
CIRCUIT
Σ
AVERAGE
Σ
HALF-BRIDGE
DRIVE
HALF-BRIDGE
DRIVE
CURRENT
SENSE
CURRENT
SENSE
ISL6315
V_IN
UGATE1
LGATE1
L1
PHASE1
V_IN
L2
UGATE2
LGATE2
PHASE2
ISEN
R_ISEN
VCC
FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6315 VOLTAGE AND CURRENT FEEDBACK
V_OUT
C_OUT
7
FN9222.1
July 18, 2007