ISL6563

FN9126 Rev 8.00

Page 7 of 20

Jun 10, 2010

For more information, refer to the ‘Output Voltage Offset

Programming’ paragraph.

SSEND (Pin 10)

This pin is an end of Soft-Start (SS) indicator; open drain

output device stays ON during soft-start, and goes open when

soft-start ends.

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

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.

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

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

FIGURE 1. SIMPLIFIED BLOCK DIAGRAM OF THE ISL6563 VOLTAGE AND CURRENT CONTROL LOOPS

DROOP

AVERAGE

CURRENT

SENSE







DAC

&

REFERENCE

PWM

CIRCUIT

PWM

CIRCUIT

HALF-BRIDGE

DRIVE

HALF-BRIDGE

DRIVE



OSCILLATOR

COMP

FB

L1

L2

UGATE1

UGATE2

LGATE1

LGATE2

PHASE1

PHASE2

ISEN

CURRENT

SENSE

VCC

R1

R2

C2

ERROR

AMP