Rainbow-electronics MAX5069 Manual do Utilizador descarregar pdf (Página 10)

MAX5069

Undervoltage Lockout

The MAX5069 features an input voltage UVLO/EN func-

tion to enable the PWM controller before any operation

can begin. The MAX5069A/D shut down if the voltage

at UVLO/EN falls below its 1.18V threshold. The

MAX5069B/C also incorporate a UVLO hysteresis input

to set the desired turn-off voltage.

MAX5069A/D UVLO Adjustment

The MAX5069A/D have an input voltage UVLO/EN with

a 1.231V threshold. Before any operation can com-

mence, the UVLO/EN voltage must exceed the 1.231V

threshold. The UVLO circuit keeps the PWM compara-

tor, ILIM comparator, oscillator, and output drivers shut-

down to reduce current consumption (see the

Functional Diagram).

Calculate R6 in Figure 2 by using the following formula:

where V

ULR2

is the UVLO/EN’s 1.231V rising threshold

and V

is the desired startup voltage. Choose an R7

value in the 20kΩ range.

After a successful startup, the MAX5069A/D shut down

if the voltage at UVLO/EN drops below its 1.18V fall-

ing threshold.

MAX5069B/C UVLO with

Programmable Hysteresis

In addition to programmable undervoltage lockout dur-

ing startup, the MAX5069B/C incorporate a UVLO/EN

ULR

617













−

High-Frequency, Current-Mode PWM Controller

with Accurate Oscillator and Dual FET Drivers

10 ______________________________________________________________________________________

MAX5069B

NDRVA

NDRVB

HYST

UVLO/EN

COMP

AGND PGND

REG5

FLTINT

OUT

SCOMP

R10

HYST

Figure 1. Nonisolated Power Supply with Programmable Input Supply Voltage

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 18 19

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