MAX5053AEUA+ Maxim Integrated Products, MAX5053AEUA+ Datasheet - Page 8

• Manufacturer Part Number: MAX5053AEUA+
• Description: IC CNTRLR PWM CRNT MD 8-UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX5053AEUA+

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 290kHz
• Duty Cycle: 50%
• Voltage - Supply: 10.8 V ~ 24 V
• Buck: No
• Boost: Yes
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Frequency-max: 290kHz
• Duty Cycle (max): 50 %
• Output Current: 1000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 262 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• Topology: Boost, Flyback
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

If V
device goes back to low-current UVLO. In this case,
increase the value of C1 in order to store enough energy
to allow for the voltage at tertiary winding to build up.
The V
diately after wake up (see Figure 1). The size of C1 and
the connection configuration of the tertiary winding
determine the number of cycles available for startup.
Large values of C1 increase the startup time but also
supply gate charge for more cycles during initial start-
up. If the value of C1 is too small, V
because NDRV does not have enough time to switch
and build up sufficient voltage across the tertiary output
which powers the device. The device goes back into
UVLO and does not start. Use a low-leakage capacitor
for C1 and C2.
As a rule of thumb, offline power supplies keep typical
startup times to less than 500ms even in low-line condi-
tions (85VAC input for universal offline or 36VDC for
telecom applications). Size the startup resistor, R1, to
supply both the maximum startup bias of the device
(90µA) and the charging current for C1 and C2. The
bypass capacitor, C2, must charge to 9.5V and C1 to
24V, all within the desired time period of 500ms.
Because of the internal 60ms soft-start time of the
MAX5052, C1 must store enough charge to deliver cur-
rent to the device for at least this much time. To calcu-
late the approximate amount of capacitance required,
use the following formula:
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
Figure 2. V
MAX5052 in Bootstrapped Mode (Figure 1)
8
IN
_______________________________________________________________________________________
Startup Time Considerations For Power
IN
drops below 9.9V before startup is complete, the
bypass capacitor, C1, supplies current imme-
IN
and V
0V
CC
Supplies Using the MAX5052
I
C
g
During Startup when Using the
1
=
=
Q
(
I
gtot
IN
+
100ms/div
V
×
hyst
I
g
f
SW
)
( )
t
SS
IN
drops below 9.9V
V
2V/div
MAX5052
V
5V/div
CC
IN
PIN
where I
startup (1.4mA), Q
f
V
the internal soft-start time (60ms).
For example:
choose 15µF standard value.
Assuming C1 > C2, calculate the value of R1 as follows:
where V
the application (36V for telecom), V
strap UVLO wake-up level (23.6V max.), I
V
For example:
choose 32kΩ standard value.
Choose a higher value for R1 than the one calculated
above if longer startup time can be tolerated in order to
minimize power loss on this resistor.
The above startup method is applicable to a circuit simi-
lar to the one shown in Figure 1. In this circuit, the tertiary
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 voltage of C1 from 22V to 10V
must be greater than the soft-start time of 60ms.
Another method for bootstrapping the power supply is to
have a separate bias winding than the one used for reg-
ulating the output voltage and to connect the bias wind-
ing so that it is in phase with the MOSFET ON time (see
Figure 3). The amount of capacitance required is much
SW
hyst
IN
supply current at startup (90µA, max).
is the MAX5052’s switching frequency (262kHz),
is the bootstrap UVLO hysteresis (12V) and t
IN
IN(MIN)
C1=
is the MAX5052’s internal supply current after
R
1
I
(
g
1.4m A+ 2.1m A
=
R
I
C1
is the minimum input supply voltage for
= (8nC) (262kHz) ≅ 2.1mA
1
(
0 72
I
=
C
=
.
(
gtot
1
36
V
(
IN MIN
24
=
I
mA
C
(
V
(
V
1
500
(
V
is the total gate charge for Q1,
) (
1 2V
SUVR
(
)
)
500
+
−
(
+
15
ms
)
I
)
−
START
12
(
ms
µ
90
)
V
)
×
F
(
SUVR
V
6 0m s
µ
C
)
)
)
A
1
= .
)
0 72
=
)
29 6
SUVR
=1 7.5µF
mA
.
k
Ω
START
is the boot-
is the
ss
is