Datasheet
6
LT1611
Transient Response
The inverting architecture of the LT1611 can generate a
very low ripple output voltage. Recently available high
value ceramic capacitors can be used successfully in
LT1611 designs with the addition of a phase lead capaci-
tor, C
PL
(see Figure 7). Connected in parallel with feedback
resistor R1, this capacitor reduces both output perturba-
OPERATIO
U
tions due to load steps and output ripple voltage to very
low levels. To illustrate, Figure 7 shows an LT1611 invert-
ing converter with resistor loads R
L1
and R
L2
.
R
L1
is
connected across the output, while R
L2
is switched in
externally via a pulse generator. Output voltage wave-
forms are pictured in subsequent figures, illustrating the
performance of output capacitor type and the effect of C
PL
connected across R1.
+
+
L1 L2
C2
–(V
IN
+ V
OUT
)
SW SWX
D1
Q1
1611 F05
C1 C3 R
LOAD
–V
OUT
V
IN
V
CESAT
+
+
L1 L2
C2
V
IN
+ V
OUT
+ V
D
SW SWX
D1
Q1
1611 F06
C1 C3 R
LOAD
–V
OUT
V
IN
V
D
Figure 5. Switch-On Phase of Inverting Converter. L1 and L2 Current Have Positive dI/dt
Figure 6. Switch-Off Phase of Inverting Converter. L1 and L2 Current Have Negative dI/dt