MAX5022EVKIT Maxim Integrated Products, MAX5022EVKIT Datasheet - Page 5

• Manufacturer Part Number: MAX5022EVKIT
• Description: EVAL KIT FOR MAX5022
• Manufacturer: Maxim Integrated Products

Specifications of MAX5022EVKIT

• Main Purpose: AC/DC, Primary Side
• Outputs And Type: 1, Isolated
• Power - Output: 5W
• Voltage - Output: 5V
• Current - Output: 1A
• Voltage - Input: 85 ~ 265VAC
• Regulator Topology: Flyback
• Frequency - Switching: 262kHz
• Board Type: Fully Populated
• Utilized Ic / Part: MAX5022
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX5021/MAX5022 are current-mode PWM con-
trollers that have been specifically designed for use in
isolated power supplies. An undervoltage lockout cir-
cuit (UVLO) with a large hysteresis (14V) along with
very low startup and operating current result in high-
efficiency, universal input power supplies. Both devices
can be used in power supplies capable of operating
from a universal 85VAC to 265VAC line or the telecom
voltage range of -36VDC to -72VDC.
Power supplies designed with these devices use a
high-value startup resistor, R
R
Figure 1). During this initial period while the voltage is
less than the UVLO start threshold, the IC typically con-
sumes only 50µA of quiescent current. This low startup
current and the large UVLO hysteresis combined with
the use of a ceramic capacitor C2 keeps the power dis-
sipation in R
the universal AC input voltage (265VAC).
The MAX5021/MAX5022 include a cycle-by-cycle cur-
rent limit which turns off the gate drive to the external
MOSFET during an overcurrent condition. If the output
on the secondary side of transformer T1 is shorted, the
tertiary winding voltage will drop below the 10V thresh-
old causing the UVLO circuit to turn off the gate drive to
the external power MOSFET, thus re-initiating the start-
up sequence.
1
SOT23
and R
—
1
2
3
4
5
6
2
) that charges a reservoir capacitor, C2 (see
PIN
Current-Mode PWM Controllers for Isolated
S
to less than 1/4W even at the high end of
PDIP
MAX
4, 5
8
7
6
3
2
1
_______________________________________________________________________________________
Detailed Description
NAME
NDRV
OPTO
GND
N.C.
V
V
CS
S
CC
IN
, (series combination of
C ur r ent S ense C onnecti on for P WM Reg ul ati on and Over cur r ent P r otecti on. The cur r ent- l i m i t
com p ar ator thr eshol d i s i nter nal l y set to 0.6V .
Power-Supply Ground
External N-Channel MOSFET Gate Connection
Gate Drive Supply. Internally regulated down from V
capacitor to GND.
IC Supply. Decouple with a 10nF or larger capacitor to GND. Connect a startup resistor
(R
See Typical Operating Circuit.
Optocoupler Transistor Collector Connection. Connect emitter of optocoupler to GND.
The OPTO has an internal pullup resistor with a typical value of 6.2k .
No Connection. Do not make connections to these pins.
s
) from the input supply line to V
Figure 2 shows the voltages on V
startup. Initially, both V
voltage is applied, C2 charges through the startup
resistor, R
the internal reference and regulator begin charging C3
(see Figure 1). The bias current consumed by the
device during this period is only 50µA; the remaining
input current charges C2 and C3. Charging of C3 stops
when the V
while the voltage across C2 continues rising until it
reaches the wakeup level of 24V. Once V
the UVLO threshold, NDRV begins switching the
MOSFET, transferring energy to the secondary and ter-
tiary outputs. If the voltage on the tertiary output builds
to higher than 10V (UVLO lower threshold), then startup
has been accomplished and sustained operation
will commence.
If V
the IC goes back into UVLO. In this case, increase the
value of C2 and/or use a MOSFET with a lower gate-
charge requirement.
The V
ly after wakeup. The size of C2 will determine the number
of cycles available for startup. Large values for C2 will
increase the startup time, but will also supply more gate
charge, allowing for more cycles after wakeup. If the
value of C2 is too small, V
IN
IN
drops below 10V before startup is complete, then
bypass capacitor C2 supplies current immediate-
IN
. Connect to bias winding through diode rectifier.
S
FUNCTION
, to an intermediate voltage at which point
CC
voltage reaches approximately 9.5V,
Power Supplies
Startup Time Considerations
IN
IN
. Decouple with a 10nF or larger
IN
and V
will drop below 10V because
Pin Description
CC
are 0V. After the line
IN
and V
IN
CC
Startup
exceeds
during
5