MAX17498A(2012) View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX17498A
(Rev.:2012)
(Rev.:2012)
Maxim Integrated
MAX17498A Datasheet PDF : 30 Pages
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MAX17498A / MAX17498B / MAX17498C
AC-DC and DC-DC Peak Current-Mode Converters
for Flyback/Boost Applications
Configuring the Power Stage (LX)
The devices use an internal n-channel MOSFET to imple-
ment internal current sensing for current-mode control
and overcurrent protection of the flyback/boost convert-
er. To facilitate this, the drain of the internal nMOSFET is
connected to the source of the external MOSFET in the
MAX17498A high-input-voltage applications. The gate of
the external MOSFET is connected to the IN pin. Ensure
by design that the IN pin voltage does not exceed the
maximum operating gate-voltage rating of the external
MOSFET. The external MOSFET gate-source voltage is
controlled by the switching action of the internal nMOS-
FET, while also sensing the source current of the exter-
nal MOSFET. In the MAX17498B/MAX17498C-based
applications, the LX pin is directly connected to either
the flyback transformer primary winding or to the boost-
converter inductor.
Maximum Duty Cycle
The MAX17498A/MAX17498C operate at a maximum
duty cycle of 49%. The MAX17498B offers a maximum
duty cycle of 92% to implement both flyback and boost
converters involving large input-to-output voltage ratios
in DC-DC applications.
Power-Good Signal (PGOOD)
The devices include a PGOOD signal that serves as
a power-good signal to the system. PGOOD is an
open-drain signal and requires a pullup resistor to the
preferred supply voltage. The PGOOD signal monitors
EA- and pulls high when EA- is 95% (typ) of its regulation
value (1.22V). For isolated power supplies, PGOOD can-
not serve as a power-good signal.
IN
REF
VCC
5V, 50mA
LDO
POK
EN/UVLO
OVI
1.23V
1.23V
10µA
LIM
10µA
SLOPE
1.23V
250mV
DECODER
33V CLAMP
(MAX17498A ONLY)
BG
CHIPEN
HICCUP
MAX17498A
MAX17498B
MAX17498C
10µA
1.17V
SSDONEF
CHIPEN
VCS
OSC
CLK
RUNAWAY
VSLOPE
VCS
VSUM
8 PEAK OR 1
RUNAWAY
SSDONE
LIMINT
VSUM
COMP
FIXED SLOPE
VARIABLE SLOPE
PEAK
CONTROL
LOGIC AND
DRIVER
PWM
PGOOD
EA-
BLOCK
VOLTAGE SS CURRENT SS
CHIPEN
SS
LX
PGND
PGOOD
COMP
EA+
EA-
Figure 1. MAX17498A/MAX17498B/MAX17498C Block Diagram
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