SP6652 Datasheet, PDF (10/16 Pages) Sipex Corporation – 1A, High Efficiency, High Frequency Current Mode PWM Buck Regulator

over frequency fzero = 80kHz (from the
Bode plot) divided by the loop gain band-
width, given as 20kHz, which is used in the
following equation:
Error Amp Gain
= fzero / (loop gain bandwidth)
= 80kHz / 20kHz
=4
The error amp transconductance is about
1mS, so this sets the RZ resistor to be:
Rz = 4/1mS = 4KΩ
We will use RZ = 4KΩ for the 3.3V output
compensation.
APPLICATIONS INFORMATION
The zero for loop compensation is placed
at the first modulator pole of 4 kHz to pro-
vide a loop response of -20/dB/decade at
the crossover frequency. The compensa-
tion capacitor Cc can be calculated from
the crossover frequency pole1 and the RZ
value:
CC = 1/(2π• RZ •pole1) = 1/(2π•4K•4kHz)
= 10nF
From the Typical Performance Charac-
teristics load step curves, the 2.5V output
and 3.3V output are stable with RZ = 4KΩ
and CC = 10nF. For 1.8V to 0.85V output,
the values RZ = 2KΩ and CC = 10nF are
recommended.
Figure 4. Typical SP6652 circuit layout.
Oct10-07 RevJ
SP6652 1A, High Efficiency, Current Mode PWM Buck Regulator
10
© 2007 Sipex Corporation