ISL6563 Intersil Corporation, ISL6563 Datasheet - Page 7

• Manufacturer Part Number: ISL6563
• Description: Two-Phase Multi-Phase Buck PWM Controller with Integrated MOSFET Drivers
• Manufacturer: Intersil Corporation

Operation
Figure 1 shows a simplified diagram of the voltage regulation
and current control loops. Both voltage and current feedback
are used to precisely regulate the output voltage and tightly
control the output currents, I
channels.
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 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.
COMP
R2
R1
C2
FB
FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6563 VOLTAGE AND CURRENT CONTROL LOOPS
SOURCE, I
DROOP
REFERENCE
ERROR
DAC
AMP
&
FB
L1
7
and I
Σ
L2
, of the two power
Σ
OSCILLATOR
Σ
Σ
AVERAGE
CIRCUIT
CIRCUIT
PWM
PWM
ISL6563
ISL6563
Current Loop
The current control loop works in a similar fashion to the
voltage control loop, but with current control information
applied individually to each channel’s Comparator. The
information used for this control is the voltage that is
developed across the r
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 ISL6563. 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.
Droop Implementation
In addition to controlling each channel’s output current, the
average channel current is used to implement an output
voltage droop characteristic. Internal average channel
current is fed into the FB pin; the voltage thus developed
across R
CURRENT
CURRENT
HALF-BRIDGE
HALF-BRIDGE
SENSE
SENSE
DRIVE
DRIVE
1
is equal to the droop voltage.
LGATE2
UGATE1
UGATE2
DS(ON)
LGATE1
PHASE1
PHASE2
ISEN
R
ISEN
of each lower MOSFET, while
V
V
IN
IN
VCC
L1
L2
C
V
OUT
OUT