ncv8881 ON Semiconductor, ncv8881 Datasheet - Page 32

• Manufacturer Part Number: ncv8881
• Description: Ncv8881 1.5a Automotive Buck Regulator With Watchdog
• Manufacturer: ON Semiconductor

Goal 1 is to have a high a unity gain bandwidth (UGB) that
is greater than 1/10 the switching frequency F
than 1/2 the switching frequency. UGB is also known as the
crossover frequency. This is the point where the loop gain =
0 dB or a gain of 1. In the plot above, the UGB is the point
where the red line crosses the TBD axis. Goal 2 is to have the
loop gain cross 0 dB with a −20 dB/decade slope also known
as a −1 slope. Goal 3 is to achieve over 45° of phase margin
when the gain crosses 0 dB. These are just goals. Sometimes
the crossover frequency is reduced below 1/10 F
to meet goal 3.
frequency as high as it can (as long as it is below 1/2 F
with a reduced phase margin of 30° in order to get a faster
transient response. The only two absolutes are that the
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
ORDERING INFORMATION
Specifications Brochure, BRD8011/D.
NCV8881PWR2G
To reiterate, there are 3 primary goals to compensating.
Conversely, some designs will push the crossover
Device
w
dB
LC
=
w
w
L
Z
ESR
1
OUT
=
1
=
R
C
2
OUT
1
ESR
C
2
1
C
OUT
SW
w
SW
Z
2
, but less
=
in order
http://onsemi.com
(
R
1
SW
+
w
Figure 59.
P
SOIC−16W EP
1
R
1
)
3
=
(Pb−Free)
)
Package
C
32
R
3
2
⎛
⎢ ⎢
⎝
C
crossover frequency cannot exceed 1/2 F
margin has to be greater than 0° at crossover. However, a
SMPS operating towards these absolutes will experience
severe ringing before it dampens out.
should be adopted.
− Place w
− Place w
− Place w
− Place w
iteration and bench testing is needed to verify results.
ON Semiconductor has developed a tool to speed up the
design process tremendously with great ease and accuracy.
This tool can be downloaded by following the link below:
http://www.onsemi.com/pub/Collateral/COMPCALC.ZIP
C
w
1
1
1
P
+
To achieve the above goals, the following guidelines
Performing these calculations will take some amount of
2
C
C
=
2
2
R
⎞
⎟ ⎟
⎠
3
1
Error Amplifier
Modulator Gain
w
Closed Loop Gain
C
Compensation Network
3
Z1
Z2
P1
P2
at w
at half the switching frequency
at half the resonance of w
at or around w
ESR
LC
1000 / Tape & Reel
Shipping
LC
SW
†
and the phase