MAX17595EVKIT# Maxim Integrated, MAX17595EVKIT# Datasheet - Page 13

• Manufacturer Part Number: MAX17595EVKIT#
• Description: Power Management IC Development Tools MAX17595 Eval Kit
• Manufacturer: Maxim Integrated

Specifications of MAX17595EVKIT#

• Rohs: yes

The MAX17595 is optimized for implementing an offline
single-switch flyback converter and has a 20V V
wake-up level with hysteresis of 15V (min). In offline
applications, a simple cost-effective RC startup circuit is
used. When the input DC voltage is applied, the startup
resistor (R
causing the voltage at the V
wake-up V
the MAX17595 draws a low startup current of 20FA (typ)
through R
wake-up V
es switching and control operations. In this condition, the
MAX17595 draws 2mA (typ) current from C
internal operation. In addition, the gate-drive current is
also drawn from C
charge of the external MOSFET used and switching fre-
quency. Since this total current cannot be supported by
the current through R
starts to drop. When suitably configured, as shown
in
NDRV pin and the flyback converter generates pulses
on bias winding NB. The soft-start period of the con-
verter should be programmed so the bias winding
pulses sustain the voltage on C
below 7V, thus allowing continued operation. The large
hysteresis of the MAX17595 allows for a small startup
capacitor (C
allows the use of a large startup resistor (R
reducing power dissipation at higher DC bus voltages.
R
resistors in series (R
applied high DC voltage in offline applications so
that the voltage across each resistor is limited to its
maximum continuous operating voltage rating. R
and C
where I
mA, Q
in nC, f
Hz, and t
back converter in ms. C
used in V
of Flyback/Boost Converter (SS)
Maxim Integrated
START
Figure
START
C
G
SW
IN
might need to be implemented as equal, multiple
START
is the gate charge of the external MOSFET used
DRV
SS
START
START
3, the external MOSFET is switched by the
is the supply current drawn at the V
IN
IN
is the switching frequency of the converter in
is the soft-start time programmed for the fly-
START
can be calculated as:
UVLO threshold (20V typ). During this time,
UVLO threshold, the MAX17595 commenc-
node in μF. See the
) charges the startup capacitor (C
. When the voltage at V
0.75
START
). The low startup current (20FA typ)
IN1





C
+
START
VDRV
VDRV
, R
0.04
, which is a function of the gate
IN
IN2
×
, the voltage on C
is a cummulative capacitor
pin to increase towards the
+
, and R
t
I
SS
IN
section.
Programming Soft-Start
Startup Operation
START
×
×
10
t
Q
SS
G
IN3
Peak-Current-Mode Controllers for
6
×
×
IN
MAX17595/MAX17596/MAX17597
) to share the
f
before it falls
0.1
SW
START
START
reaches the





µ
IN
IN
Flyback and Boost Regulators
F
START
), thus
START
START
UVLO
pin in
for its
),
Figure 2. Programming EN/UVLO and OVI
where C
For designs that cannot accept power dissipation in the
startup resistors at high DC input voltages in offline appli-
cations, the startup circuit can be set up with a current
source instead of a startup resistor as shown in
The startup capacitor (C
the above equation:
Resistors R
The V
MAX17597 is set to 4.1V (typ) with a 200mV hyster esis,
optimized for low-voltage DC-DC applications down to
4.5V. For applications where the input DC voltage is low
enough (e.g., 4.5V to 5.5V DC) that the power loss
incurred to supply the operating current of the MAX17596/
MAX17597 can be tolerated, the V
connected to the DC input, as shown in
case of higher DC input voltages (e.g., 16V to 32V DC),
a startup circuit, such as that shown in
used to minimize power dissipation. In this startup
IN
START
R
SUM
UVLO wake-up threshold of the MAX17596/
SUM
R
START
=
is the startup capacitor in FF.
and R
=
R
R
R
R
R
R
R
SUM
DC1
DC2
DC3
EN
OVI
ISRC
=
ISRC
(
V
START
START


1 C
EN/UVLO
OVI
V
+
V
can be calculated as:
START
BEQ1
10
70
START
) can be calculated using
−
10
M
M
)
MAX17595
MAX17596
MAX17597
W
×
W


50
IN
Figure
Figure
k
pin is directly
I
Figure
6, can be
5. In the
4.
13