L6727

Application details

Doc ID 12933 Rev 4

15/34

9

Application details

9.1

Output voltage selection

L6727 is capable to precisely regulate an output voltage as low as 0.8 V. In fact, the device

comes with a fixed 0.8 V internal reference that guarantees the output regulated voltage to

be within ±1 % tolerance over line and temperature variations between 0 °C and +70 °C

(excluding output resistor divider tolerance, when present).

FB pin and ground. Referring to Figure 1, the steady state DC output voltage will be:

9.2

Compensation network

The control loop showed in Figure 6 is a voltage mode control loop. The error amplifier is a

voltage mode type. The output voltage is regulated to the internal reference (when present,

offset resistor between FB node and GND can be neglected in control loop calculation).

Error Amplifier output is compared to oscillator saw-tooth waveform to provide PWM signal

amplitude. This waveform is filtered by the output filter.

The converter transfer function is the small signal transfer function between the output of the

ΔV

function ideally equal to -Z

Figure 6.

PWM control loop

V

OUT

V

REF

1

R

FB

R

OS

-----------

+

⎝⎠

⎛⎞

⋅

=

L

R

C

OUT

ESR

R

F

C

F

C

P

R

FB

C

S

OSC

V

IN

ΔV

OSC

+

+

_

_

V

OUT

V

REF

Z

FB

PWM

COMPARATOR

ERROR

AMPLIFIER

R

S