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MAX17498A
(Rev.:2012)

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

Pin Description (continued)

PIN

NAME

FUNCTION

13

PGOOD

Open-Drain Output. PGOOD goes high when EA- is within 5% of the set point. PGOOD pulls low when

EA- falls below 92% of its set-point value.

14

PGND Power Ground for Converter

15

LX

External Transformer/Inductor Connection for the Converter

16

IN

Internal Linear Regulator Input. Connect IN to the input-voltage source. Bypass IN to PGND with a 1µF

(min) ceramic capacitor.

—

EP

Exposed Pad. Internally connected to SGND. Connect EP to a large copper plane at SGND potential to

(SGND) provide adequate thermal dissipation. Connect EP (SGND) to PGND at a single point.

Detailed Description

The MAX17498A offers a bootstrap UVLO wakeup level

of 20V with a wide hysteresis of 15V (min) optimized

for implementing an isolated and nonisolated universal

(85V AC to 265V AC) offline single-switch flyback

converter or telecom (36V to 72V) power supplies. The

MAX17498B/MAX17498C offer a UVLO wakeup level of

4.4V and are well suited for low-voltage DC-DC flyback/

boost power supplies. An internal reference (1.22V)

can be used to regulate the output down to 1.23V in

nonisolated flyback and boost applications. Additional

semi-regulated outputs, if needed, can be generated

by using additional secondary windings on the flyback

converter transformer. A flexible error amplifier and REF

allow the end-user selection between regulating positive

and negative outputs.

The devices utilize peak current-mode control and exter-

nal compensation for optimizing the loop performance for

various inductors and capacitors. The devices include a

cycle-by-cycle peak current limit and eight consecutive

occurrences of current-limit event trigger hiccup mode,

that protect external components by halting switching for

a period of time (32ms). The devices also include voltage

soft-start for nonisolated designs and current soft-start

for isolated designs to allow monotonic rise of the output

voltage. The voltage or current soft-start can be selected

using the SLOPE pin. See the Block Diagram for more

information.

Input Voltage Range

The MAX17498A has different rising and falling UVLO

thresholds on the IN pin than those of the MAX17498B/

MAX17498C. The thresholds for the MAX17498A are

optimized for implementing power-supply startup

schemes typically used for offline AC-DC power supplies.

The MAX17498A is therefore well suited for opera-

tion from the rectified DC bus in AC-DC power-supply

applications typically encountered in front-end industrial

power-supply applications. As such, the MAX17498A

has no limitation on the maximum input voltage as long

as the external components are rated suitably and the

maximum operating voltages of the MAX17498A are

respected. The MAX17498A can successfully be used

in universal input-rectified (85V to 265V AC) bus applica-

tions, rectified 3-phase DC bus applications, and tele-

com (36V to 72V DC) applications.

The MAX17498B/MAX17498C are intended for imple-

menting a flyback (isolated and nonisolated) and

boost converter with an on-board 65V rated n-channel

MOSFET. The IN pin of the MAX17498B/MAX17498C has

a maximum operating voltage of 36V. The MAX17498B/

MAX17498C implement rising and falling thresholds on

the IN pin that assume power-supply startup schemes,

typical of lower voltage DC-DC applications, down to an

input voltage of 4.5V DC. Therefore, flyback converters

with a 4.5V to 36V supply voltage range can be imple-

mented with the MAX17498B/MAX17498C.

Internal Linear Regulator (VCC)

The internal functions and driver circuits are designed

to operate from a 5V Q5% power-supply voltage. The

devices have an internal linear regulator that is powered

from the IN pin and generates a 5V power rail. The output

of the linear regulator is connected to the VCC pin and

should be decoupled with a 2.2µF capacitor to ground

for stable operation. The VCC converter output supplies

the operating current for the devices. The maximum

operating voltage of the IN pin is 29V for the MAX17498A

and 36V for the MAX17498B/MAX17498C.

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