Datasheet

MAX1960/MAX1961/MAX1962
where:
V
IN(MAX)
= Maximum input voltage
V
RAMP
= Oscillator ramp voltage = 0.85 x 10
6
/f
S
,
where f
S
= switching frequency
L
O
= Output inductance
C
O
= Output capacitance
The goal is to place the two zeros below crossover and
the two poles above crossover so that crossover
occurs with a single-pole slope. The compensation pro-
cedure is as follows:
Select the crossover frequency such that:
f
0
< f
ZESR
and f
0
<1/5  f
S
Select R1 such that:
where g
mEA
= 2mS.
Place the first zero before the double pole:
Place the third pole at half the switching frequency:
If C2 < 10pF, it can be omitted.
Place the second pole after the ESR zero:
If:
where g
mEA
= 2mS
increase R1 and recalculate C1, C2, and C3.
Place the second zero at the double-pole frequency:
Set the output voltage:
R
V
VV
RV V
FB
OUT FB
FB
4308=×=
-
,.
R
fC
R
LC
3
1
23
2≥
××π
-
R
g
mEA
2
1
< ,
R
fC
ZESR
2
1
23
≤
××π
C
fL C V
RV
RAMP
IN
3
2
1
00 0
≤
×× × ×
×
π
C
fR
S
2
1
205 1
≥
×××π .
C
fR
LC
1
1
2 0 75 1
≥
×××π .
R
g
mEA
1
2
>>
2.35V to 5.5V, 0.5% Accurate, 1MHz PWM
Step-Down Controllers with Voltage Margining
16 ______________________________________________________________________________________
DH
V
IN
L
O
C
0
R3
R4
R2
R1
C1C2
C3
V
OUT
LX
DL
FB
COMP
MAX1960
Figure 5. Type 3 Compensation Network
fp1
fz1 fz2 fp2
fp3
GAIN (dB)
FREQUENCY
Figure 6. Transfer Function for Type 3 Compensation