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MAX17498A

AC-DC and DC-DC Peak Current-Mode Converters for Flyback/Boost Applications

Maxim Integrated 

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 converter. To

facilitate this, the drain of the internal nMOSFET is connect-

ed 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 switch-

ing action of the internal nMOSFET, while also sensing the

source current of the external MOSFET. In the MAX17498B/

MAX17498C-based applications, the LX pin is directly con-

nected 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 94%. The MAX17498B offers a maximum

duty cycle of 92%. The devices can be used to imple-

ment 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

POK

EN/UVLO

1.23V

OVI

1.23V

LDO

33V CLAMP

(MAX17498A ONLY)

BG

VCS

10µA

SSDONE

SSDONE

VOLTAGE SS

CHIPEN

HICCUP

SS

CURRENT SS

MAX17498A

1.17V

MAX17498B

MAX17498C

SS

SSDONEF

CHIPEN

OSC

VSLOPE

VCS

VSUM

LX

CLK

RUNAWAY

SSDONE

1 RUNAWAY

10µA

LIM

10µA

SLOPE

1.23V

250mV

DECODER

LIMINT

VSUM

COMP

FIXED SLOPE

VARIABLE SLOPE

VOLTAGE SS CURRENT SS

PEAK

CONTROL

LOGIC AND

DRIVER

PWM

EA-

PGOOD

BLOCK

CHIPEN

PGND

PGOOD

COMP

EA+

EA-

Figure 1. MAX17498A/MAX17498B/MAX17498C Block Diagram

Maxim Integrated

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