MAX17497A 查看數據表（PDF） - Maxim Integrated

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MAX17497A

AC-DC and DC-DC Peak Current-Mode Converters with Integrated Step-Down Regulator

Maxim Integrated 

MAX17497A/MAX17497B

AC-DC and DC-DC Peak Current-Mode Converters

with Integrated Step-Down Regulator

Pin Description (continued)

PIN

NAME

FUNCTION

8

SSF

Soft-Start Pin for Flyback/Boost Converter. Connect a capacitor from SSF to SGND to set the

soft-start time interval.

9

OUTB

Feedback for Step-Down Regulator. Connects OUTB to the positive terminal of the step-down

regulator output capacitor.

10

PGNDB Power Ground for Step-Down Regulator

11

LXB

External Inductor Connection for Step-Down Regulator. Connect to one end of the output inductor.

Connect the other end of output inductor to output capacitor.

Internal Step-Down Regulator Input. Connect INB to either VOUTF, the output of flyback/boost

12

INB

converter, or directly to the DC input source, as needed in the application. Bypass INB to PGNDB

with a 2.2FF minimum ceramic capacitor.

13

RESETN

Open-Drain Output. RESETN goes high when both the outputs are within 5% of their regulation point.

RESETN goes low when either of the outputs falls below 92% of their regulation value.

14

PGNDF

Power Ground for Flyback/Boost Converter

15

LXF

External Transformer/Inductor Connection for Flyback/Boost Converter

16

IN

Internal Linear Regulator Input. Connect IN to the input-voltage source. Bypass IN to PGNDF with

ceramic capacitor of at least 1FF.

—

EP

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

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

Detailed Description

The MAX17497A is optimized for implementing a noniso-

lated offline flyback converter with output power of up to

30W and a 3.3V, 600mA power rail using the on-board

synchronous step-down regulator. The output voltage of

the flyback converter serves as the input supply voltage

to the on-board 3.3V integrated synchronous step-down

regulator. The outputs of the flyback converter and step-

down regulator are regulated with independent feedback

loops, thus providing two accurately controlled voltages

for the system. If needed, more semi-regulated outputs

can be generated using additional secondary windings

on the flyback converter transformer. The MAX17497B is

optimized for implementing a nonisolated flyback/boost

converter up to 15W and a 3.3V, 600mA synchronous

step-down regulator in low-voltage DC-DC applications

down to 4.5V DC. See the Figure 1 for more information.

Input Voltage Range

The MAX17497A has different rising and falling UVLO

thresholds on the IN pin than those of the MAX17497B.

The thresholds for the MAX17497A are optimized for

implementing power-supply startup schemes typically

used for offline AC-DC power supplies. The MAX17497A

is therefore well suited for operation from the recti-

fied DC bus in AC-DC power-supply applications typi-

cally encountered in electric metering and other low-

power industrial power-supply applications. As such,

the MAX17497A has no limitation on the maximum

input voltage as long as the external components are

rated suitably and the maximum operating voltages of

the MAX17497A are respected. The MAX17497A can

successfully be used in universal input rectified (85V to

265V AC) bus applications, rectified 3-phase DC bus

applications, and telecom (36V to 72V DC) applications.

Maxim Integrated

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