ISL6590DR datasheet(17/24 Pages) INTERSIL

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Compensation Methodology

Due to the user interface software interface, it is very easy to

change the frequency compensation and see the resulting

performance on a scope or network analyzer. Transient

response is viewed by applying a transient load and

monitoring the output voltage with a scope. Frequency

response is viewed by placing a small resistor between the

output and the feed back network, applying a small sine

wave at the input to the feed back network and measuring

the amplitude and phase shift of the resulting sine wave on

the output. Sweeping the frequency produces plots similar

to those above.

Frequency Domain

It is recommended to place the first zero (FZ1) at the

resonant frequency of the output inductors and capacitors (F

= 1/(2

π√LC) = 10kHz in this case). Then increase F

Z2 and

FP0 to maximize DC gain and the frequency at which gain

drops below 0dB while keeping the phase margin above 60

degrees. Phase Margin is the difference between 180

degrees and the phase shift of the loop at the frequency

where the gain drops below 0dB (cross over frequency). If

the loops phase shift reaches 180 degrees and has gain

equal to or greater than 0dB, it acts as positive feed back

and the loop will oscillate. Even if the loops phase shift is

slightly below 180 degrees at the cross over frequency, the

loop will respond to transients with overshoot and ringing.

Loop phase shift between 90 and 120 degrees at the cross

over frequency (Phase margin = 60 to 90 degrees) results in

little or no over shoot and ringing. Large phase margins

(>90 degrees) result in slower transient response.

Time Domain

It is recommended to place the first zero (FZ1) at the

resonant frequency of the output inductors and capacitors (F

= 1/(2

π√LC = 10kHz in this case). Then increase FZ2 and

FP0 to minimize response time over (under) shoot and

ringing. The first microseconds of transient response are

primarily dependant on the ESR and ESL of the output

capacitors. After the affects of ESL and ESR pass the loop

must control the response.

User Interface Software

The ISL6590 controller and the ISL6580 intelligent power

stage have programmable values that can be changed using

the User Interface Software. The loop configuration and

system performance is adjusted using the software. The use

of the software allows the engineer to evaluate the system

performance without having to physically change

components on the board. Primarion PowerCode user

interface software (provided by Intersil and our partner

Primarion).

Below are screen shots showing data entry points, pull down

menus, buttons for help and a tutorial. The user interface

software allows the designer to adjust the load line,

frequency response, ATR and protection modes.

FIGURE 20. PID COMPENSATOR FREQUENCY RESPONSE

100

1000

10000

Frequency (in KHz)

-90

-80

-70

-60

-50

-40

-30

-20

-10

Compensation

Phase

FIGURE 21. FREQUENCY RESPONSE OF THE CLOSED LOOP

-120

-100

-80

-60

-40

-20

100

1000

10000

Frequency (in KHz)

-50

100

150

200

250

300

350

400

Loop

Phase

FIGURE 22. TYPICAL RESPONSE TO A LOAD TRANSIENT

ISL6590

ISL6590DR Datasheet(PDF) 17 Page - Intersil Corporation

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