Datasheet

LT6110
30
6110fa
For more information www.linear.com/LT6110
applicaTions inForMaTion
positive-going phase near the loop’s crossover frequency
and is adjusted for an optimum phase margin. Regulator
loop compensation, transient response and stability are
covered in depth in AN76.
An LT6110 in the control loop introduces a pole near
160kHz (from the Typical Performance Curves) and this
pole reduces the loop’s optimized phase margin resulting
in load transient overshoot and possibly ringing. Adding
a capacitor, C
COMP
in parallel with the regulator’s feed-
back resistance,
R
FA
introduces a zero to compensate the
effects of the LT6110 pole. The frequency of the R
FA
and
C
COMP
zero is best adjusted during a load transient test.
Start with a C
COMP
value for a zero equal to or less than
160kHz (the LT6110 pole), then increase C
COMP
for a load
transient that settles with minimal overshoot or ringing.
Figure 23 shows an LT3980 buck regulator with an LT6110
circuit used for transient response testing and with the
added zero to restore the loop’s phase margin. During
the circuit’s load transient testing, a C
COMP
value of 1nF
Figure 22. A Small-Signal Model: Current Mode Buck Regulator with an LT6110
Figure 23. Load Transient Response Test Circuit Using an LT3980 Buck Regulator with an LT6110
15k
1.5nF
0.1µF
10µF
100pF
V
IN
V
IN
BD
RUN/SS
0.47µF
47µF
C
COMP
1nF
V
REG
R
FA
6.49k
R
FB
412k
10µH
LT3980
GND
100k
R
G
80.6k
97.6k
BOOST
NC +IN
IOUT
LT6110
V
+
RS
IMON
–INV
–
20mΩ
PGOOD SW
R
T
DA
V
C
FB
6110 F23
1A
180pF
1.6A
2k
R
WIRE
0.3Ω
R
IN
402Ω
5Ω 8Ω
V
LOAD
V
IN
C
O
C
COMP
R
FA
R
FB
L
BUCK REGULATOR MODEL
R
ESR
V
REF
V
FB
ERROR
AMPLIFIER
g
e
IS THE ERROR
AMPLIFIER
TRANSCONDUCTANCE
MODULATOR
g
m
IS THE
MODULATOR
TRANSCONDUCTANCE
V
C
R
Q
OSCILLATOR
SLOPE COMP
R
G
LT6110
LT6110 MODEL
R1 R
e
6110 F22
V
LOAD
V
REG
R
WIRE
R
SENSE
R
LOAD
C1
C2
I
IOUT
+
–
R
IN
+
–
+
–
S