MAX5068 Maxim Integrated Products, MAX5068 Datasheet - Page 13

• Manufacturer Part Number: MAX5068
• Description: Current-Mode PWM Controller
• Manufacturer: Maxim Integrated Products

Figure 6. Secondary-Side, Regulated, Isolated Power Supply
Assuming C1 > C3, calculate the value of R1 as follows:
where V
(23.6V max), V
age for the application (36V for telecom), and I
the V
For example:
High-Frequency, Current-Mode PWM Controller
IN
supply current at startup (90µA, max).
R
R
SUVR
1
1
I
C1
≅
≅
I
C
=
V
106
IN(MIN)
1
is the bootstrap UVLO wakeup level
V
IN MIN
IN
36
(
24
=
______________________________________________________________________________________
C2
C3
C4
µ
R2
R3
R4
V
with Accurate Programmable Oscillator
V x
A
I
500
V
C
)
1
SUVR
−
is the minimum input supply volt-
+
−
500
+
ms
12
2 2
90
.
0 5 .
I
V
START
µ
ms
µ
FLTINT
V
REG5
RT
DT
SYNC
AGND
C1
CC
×
A
F
R1
x V
C
=
=
MAX5068A
D2
1
SUVR
106
122 4
IN
µ
.
UVLO/EN
PGND
A
k
COMP
NDRV
HYST
Ω
CS
FB
START
R5
is
C5
To minimize power loss on this resistor, choose a high-
er value for R1 than the one calculated above (if a
longer startup time can be tolerated).
The above startup method is applicable to a circuit sim-
ilar to the one shown in
tiary winding has the same phase as the output
windings. Thus, the voltage on the tertiary winding at
any given time is proportional to the output voltage and
goes through the same soft-start period as the output
voltage. The minimum discharge time of C1 from 22V to
10V must be greater than the soft-start time (t
Use an external resistor at RT to program the MAX5068
internal oscillator frequency from 50kHz to 2.5MHz. The
MAX5068A/B output switching frequency is one-half of
the programmed oscillator frequency with a 50% duty
cycle. The MAX5068C/D/E/F output switching frequen-
cy is one-quarter of the programmed oscillator frequen-
cy with a 75% duty cycle.
R6
R
R7
HYST
Q1
R
R8
CS
R9
Oscillator/Switching Frequency
V
CC
R10
D1
PS2913
MAX8515
Figure 1. In this circuit, the ter-
VOUT
C10
R11
C7
C6
R12
R13
SS
).
13