Rainbow-electronics MAX5095A Bedienungsanleitung PDF herunterladen (Seite 13)

and Startup

In normal operation, V

is derived from a tertiary wind-

ing of the transformer. However, at startup there is no

energy delivered through the transformer, thus a resistor

must be connected from V

to the input power source

(see R

and C

in Figures 5 to 8). During startup, C

charges up through R

. The 5V reference generator,

comparator, error amplifier, oscillator, and drive circuit

remain off during UVLO to reduce startup current below

65µA. When V

reaches the undervoltage-lockout

threshold of 8.4V, the output driver begins to switch and

the tertiary winding supplies power to V

. V

has an

internal 26.5V current-limited clamp at its input to protect

the device from overvoltage during startup.

Size the startup resistor, R

, to supply both the maxi-

mum startup bias (I

START

) of the device (65µA max)

and the charging current for C

. The startup capacitor

must charge to 8.4V within the desired time period

(for example, 500ms). The size of the startup

capacitor depends on:

1) IC operating supply current at a programmed oscilla-

tor frequency (f

OSC

2) The time required for the bias voltage, derived from

a bias winding, to go from 0 to 9V.

3) The MOSFET total gate charge.

4) The operating frequency of the converter (f

MAX5094A/B/C/D/MAX5095A/B/C

High-Performance, Single-Ended, Current-Mode

PWM Controllers

______________________________________________________________________________________ 13

UVLO

REFERENCE

2.5V

PREREGULATOR

VOLTAGE-

DIVIDER

THERMAL

SHUTDOWN

EN-REF

SNS

5V REGULATOR

VOLTAGE-

DIVIDER

26.5V

REF

2.5V

REG_OK

DELAY

OSC Q

OUT

ILIM

CPWM

0.3V

EN-DRV-BAR

GND

COMP

ADV_CLK

CLK

MAX5095C

2.5V

50% MAX DUTY CYCLE

8.4V/7.6V

Figure 3. MAX5095C Functional Diagram

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 21 22

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics MAX5095A Bedienungsanleitung Seite 13

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Sensoren Rainbow-electronics MAX5095A