MAX5068 데이터 시트보기 (PDF) - Maxim Integrated
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MAX5068
Maxim Integrated
MAX5068 Datasheet PDF : 20 Pages
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High-Frequency, Current-Mode PWM Controller
with Accurate Programmable Oscillator
D2
VIN
R1
C1
R2
IN
NDRV
Q1
C2
FLTINT
CS
C3
VCC
FB
RCS
C4
MAX5068A
R5 C5
REG5
R3
COMP
R6
RT
UVLO/EN
R4
DT
RHYST
SYNC
HYST
AGND
PGND
R7
D1
VOUT
C6
R8
R9
Figure 1. Nonisolated Power Supply with Programmable Input Supply Voltage
Use the MAX5068C/D/E/F in forward converter applica-
tions with greater than 50% duty cycle. The large duty
cycle results in much lower operating primary RMS cur-
rent through the MOSFET switch and, in most cases,
requires a smaller output filter capacitor. The major dis-
advantage to this is that the MOSFET voltage rating
must be higher. The MAX5068C/D/E/F capacitor
adjustable-slope-compensation feature allows for easy
stabilization of the inner current loop.
Undervoltage Lockout
The MAX5068 features an input voltage UVLO/EN func-
tion to enable the PWM controller before any operation
can begin. The MAX5068C/E shut down if the voltage
at UVLO/EN falls below its 1.18V threshold. The
MAX5068A/B/D/F also incorporate an UVLO hysteresis
input to set the desired turn-off voltage.
MAX5068C/E UVLO Adjustment
The MAX5068C/E 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 driver shut
down to reduce current consumption (see the
Functional Diagram).
Calculate R6 in Figure 2 by using the following formula:
R6
=
⎛ VON
⎝⎜ VULR2
⎞
− 1⎠⎟
×
R7
where VULR2 is the UVLO/EN’s 1.231V rising threshold
and VON is the desired startup voltage. Choose an R7
value in the 20kΩ range.
After a successful startup, the MAX5068C/E shut down if
the voltage at UVLO/EN drops below its 1.18V threshold.
10 ______________________________________________________________________________________
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