LTC3722-2 Linear Technology, LTC3722-2 Datasheet - Page 23

• Manufacturer Part Number: LTC3722-2
• Description: Synchronous Dual Mode Phase Modulated Full Bridge Controllers
• Manufacturer: Linear Technology

OPERATIO
Step 2. Calculate ESR zero location:
Step 3. Calculate the feedback divider gain:
If Polymer electrolytic output capacitors are used, the ESR
zero can be employed in the overall loop compensation
and optimum bandwidth can be achieved. If aluminum
electrolytics are used, the loop will need to be rolled off
prior to the ESR zero frequency, making the loop response
slower. A linearized SPICE macromodel of the control loop
is very helpful tool to quickly evaluate the frequency
response of various compensation networks.
F
F
F
R
P1(MIN)
P1(MAX)
Z1
B
/(R
= 1/(2 • R
B
+ R
= 1/(2 • R
= 1/(2 • R
T
) or V
ESR
U
REF
• C
O(MAX)
O(MIN)
/V
O
OUT
)
• C
• C
O
O
)
)
R
L
Figure 13. Compensation for Polymer Electrolytic
ESR
C
O
V
OUT
R
R
D
I
2.5V
REF
LT1431 OR EQUIVALENT
AMP AND REFERENCE
PRECISION ERROR
R
f
+
–
C
P2
Polymer Electrolytic (see Figure 13) 1/(2 C
low frequency pole. 1/(2 C
zero. The zero frequency should coincide with the worst-
case lowest output pole frequency. The pole frequency
and mid frequency gain (R
the loop crosses over zero dB with a –1 slope at a
frequency lower than (f
cally display the frequency response. An optional higher
frequency pole set by CP2 and R
switching frequency noise.
Aluminum Electrolytic (see Figure 13) the goal of this
compensator will be to cross over the output minimum
pole frequency. Set a low frequency pole with C
at a frequency that will cross over the loop at the output
pole minimum F, place the zero formed by C
output pole F.
OPTIONAL
C
C
COLL
LTC3722-1/LTC3722-2
V
OUT
OPTO
1922 F12
COMP
SW
F
/8). Use a bode plot to graphi-
/R
C
R
I
) should be set such so that
F
) sets the low frequency
www.DataSheet4U.com
f
is used to attenuate
C
and R
C
R
C
I
) sets a
and R
23
f
at the
372212i
IN