Datasheet

MAX17595/MAX17596/MAX17597
Peak-Current-Mode Controllers for
Flyback and Boost Regulators
14Maxim Integrated
scheme, the transistor (Q1) supplies the switching cur-
rent until a bias winding NB comes up and turns off Q1.
The resistor (R
Z
) can be calculated as:
−
=×W
Z INMIN
R 2 (V 6.3) k
Programming Soft-Start (SS)
The soft-start period for the devices can be programmed
by selecting the value of the capacitor C
SS
connected
from the SS pin to SGND. Capacitor C
SS
can be calcu-
lated as:
SS SS
C 8.2645 t nF= ×
where t
SS
is expressed in ms. This equation is directly
applicable to the boost converter application circuit of
Figure 11. For optoisolated converters, the soft-start
period is approximately equal to 30% of t
SS
when the
Figure 3. MAX17595 RC-Based Startup Circuit
Figure 4. MAX17595 Current-Source-Based Startup Circuit
V
DRV
V
DC
C
OUT
V
IN
V
OUT
C
VDRV
C
START
LDO DRV
CS
NDRV
D1
D2
NS
NP
NB
MAX17595
V
DC
R
IN1
R
START
R
IN2
R
IN3
R
IN1
V
DC
R
SUM
R
IN2
V
DRV
V
DC
C
OUT
D1
V
IN
R
ISRC
V
OUT
C
VDRV
R
S
C
START
R
IN3
LDO DRV
CS
NDRV
D2
NS
NP
NB
MAX17595