Owner manual
MAX5099
Calculate the temperature rise of the die using the fol-
lowing equation:
T
J
= T
C
x (P
T
x θ
JC
)
where θ
JC
is the junction-to-case thermal impedance of
the package equal to +1.7°C/W. Solder the exposed
pad of the package to a large copper area to minimize
the case-to-ambient thermal impedance. Measure the
temperature of the copper area near the device at a
worst-case condition of power dissipation, and use
+1.7°C/W as θ
JC
thermal impedance.
Compensation
The MAX5099 provides an internal transconductance
amplifier with its inverting input and its output available
for external frequency compensation. The flexibility of
external compensation for each converter offers wide
selection of output filtering components, especially the
output capacitor. For cost-sensitive applications, use
high-ESR aluminum electrolytic capacitors; for compo-
nent size-sensitive applications, use low-ESR tantalum,
polymer, or ceramic capacitors at the output. The high
switching frequency of the MAX5099 allows the use of
ceramic capacitors at the output.
Choose all the passive power components that meet
the output ripple, component size, and component cost
requirements. Choose the small-signal components for
the error amplifier to achieve the desired closed-loop
bandwidth and phase margin. Use a simple pole-zero
pair (Type II) compensation if the output capacitor ESR
zero frequency is below the unity-gain crossover
frequency (f
C
). Type III compensation is necessary
when the ESR zero frequency is higher than f
C
or when
compensating for a continuous-mode boost converter
that has a right-half-plane zero.
Use procedure 1 to calculate the compensation
network components when f
ZERO,ESR
< f
C
.
Buck Converter Compensation
Procedure 1 (See Figure 3)
1) Calculate the f
ZERO,ESR
and LC double-pole
frequencies:
2) Select the unity-gain crossover frequency:
If the f
ZERO,ESR
is lower than f
C
and close to f
LC
, use a
Type II compensation network where R
F
C
F
provides a
midband zero f
MID,ZERO
, and R
F
C
CF
provides a high-
frequency pole.
3) Calculate modulator gain G
M
at the crossover
frequency.
where V
OSC
is a peak-to-peak ramp amplitude equal
to 1V.
The transconductance error-amplifier gain is:
G
E/A
= g
M
x R
F
The total loop gain at f
C
should be equal to 1:
G
M
x G
E/A
= 1
or
4) Place a zero at or below the LC double-pole:
5) Place a high-frequency pole at f
P
= 0.5 x f
SW
.
C
C
fRC
CF
F
SW F F
=
×××
()
−205 1π .
C
Rf
F
FLC
=
××
1
2π
R
V ESR f L V
V g ESR
F
OSC C OUT OUT
IN M
=
+××
()
×
×××
2
08
π
.
G
V
V
ESR
ESR f L V
M
IN
OSC C OUT OUT
=×
+××
()
×
2
08
π
.
f
f
C
SW
≤
20
f
ESR C
f
LC
ZERO ESR
OUT
LC
OUT OUT
,
=
××
=
×
1
2
1
2
π
π
R
1
FB_
R
F
COMP_
V
OUT
V
REF
C
CF
C
F
R
2
-
+
g
M
Figure 3. Type II Compensation Network
Dual, 2.2MHz, Automotive Synchronous Buck
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 21