LT3579 LINER [Linear Technology], LT3579 Datasheet - Page 28

• Manufacturer Part Number: LT3579
• Description: 6A Boost/Inverting DC/DC Converter with Fault Protection
• Manufacturer: LINER [Linear Technology]

LT3579/LT3579-1
APPENDIX
Table 7 shows a list of several discrete PMOS manufa-
cturers. Consult the manufacturers for detailed information
on their entire selection of PMOS devices.
Table 7. Discrete PMOS Manufacturers
Vishay
Fairchild Semiconductor
Central Semiconductor
COMPENSATION – ADJUSTMENT
To compensate the feedback loop of the LT3579, a series
resistor-capacitor network in parallel with an optional single
capacitor must be connected from the V
most applications, choose a series capacitor in the range
of 1nF to 10nF with 2.2nF being a good starting value.
The optional parallel capacitor should range in value from
22pF to 180pF with 47pF being a good starting value. The
compensation resistor, R
50k. A good technique to compensate a new application is
to use a 100kΩ potentiometer in place of the series resistor
R
47pF respectively, adjust the potentiometer while observing
the transient response and the optimum value for R
be found. Figures 17a to 17c illustrate this process for the
circuit of Figure 20 with a load current stepped between
0.7A and 1.5A. Figure 17a shows the transient response
with R
by the excessive ringing in the output voltage and inductor
current. In Figure 17b, the value of R
which results in a more damped response. Figure 17c
shows the results when R
transient response is nicely damped and the compensation
procedure is complete.
COMPENSATION – THEORY
Like all other current mode switching regulators, the
LT3579 needs to be compensated for stable and effi cient
operation. Two feedback loops are used in the LT3579: a
fast current loop which does not require compensation,
and a slower voltage loop which does. Standard Bode plot
analysis can be used to understand and adjust the voltage
28
C
. With the series and parallel capacitors at 2.2nF and
C
equal to 1k. The phase margin is poor as evidenced
www.vishay.com
www.fairchildsemi.com
www.centralsemi.com
C
C
, is usually in the range of 5k to
is increased further to 8k. The
C
is increased to 3.5k,
C
pin to GND. For
C
can
Figure 17a. Transient Response Shows Excessive Ringing
Figure 17c. Transient Response Is Well Damped
AC COUPLED
AC COUPLED
AC COUPLED
500mV/DIV
500mV/DIV
500mV/DIV
Figure 17b. Transient Response Is Better
2A/DIV
1A/DIV
2A/DIV
1A/DIV
2A/DIV
1A/DIV
I
I
I
V
LOAD
V
LOAD
V
LOAD
OUT
OUT
OUT
I
I
I
L
L
L
R
R
R
C
C
C
= 3.5k
= 8k
= 1k
100μs/DIV
100μs/DIV
100μs/DIV
3579 F17a
3579 F17b
3579 F17c
35791f