
M
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
8
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Pin Description
PIN
MAX8540
MAX8541
NAME
FUNCTION
1
1
REF
5V Reference Voltage Output. Bypass to ground with a 1μF capacitor. REF is pulled to GND
during shutdown.
2
2
OV
System Input Overvoltage Monitoring. The OV threshold is 3.021V with 130mV hysteresis.
Connect to the center of a resistor-divider from the system input to GND to set the overvoltage
trip point (see the
Overvoltage Threshold
section).
3
3
UV
System Input Undervoltage Monitoring and Feed-Forward Input. The UV threshold is 1.25V with
120mV hysteresis. Connect to the center of a resistor-divider from the system input to GND to
set the undervoltage trip point (see the
Undervoltage Threshold
section). This input can be used
as a disable input by pulling it below 1.2V. UV remains active during shutdown.
4
4
FREQ/
SYNC
P og am m ab e Fr eq uency and S ync Inp ut. C onnect a r esi stor i n p ar al el w h RC ( 10k
0.01μF) fr om
FRE Q/S Y N C to GN D to set the sw chi ng fr eq uency or ap p y an exter nal cl ock si g nal thr oug h a d od e
to synchr oni ze to an exter nal fr eq uency.
5
5
SS
S oft- S ar C ap aci or C onnecti on. C onnect a cap aci or fr om S S to GN D to set the soft- star ti m e p er od
Programmable Maximum Duty-Cycle Input. Connect a resistor from MAXDTY to GND to set the
maximum duty cycle for minimum system input voltages. The maximum duty cycle is inversely
proportional to the system input voltage. The higher the input voltage, the less the maximum
duty cycle. The maximum duty cycle is internally limited to 80% at any switching frequency.
MAXDTY is high impedance during shutdown. Bypass MAXDTY with a 2200pF capacitor.
6
6
MAXDTY
7
7
EN
Active-Low Enable Input. Drive
EN
to GND to enable the IC. Drive high to place the IC in
shutdown mode.
8
—
SCOMP
Programmable Slope Compensation Input. Connect a resistor from SCOMP to GND to set the
slope compensation.
—
8
PRAMP
Programmable Voltage-Mode Control-Ramp Input. Connect a resistor from PRAMP to GND to
set the magnitude of the voltage ramp.
9
9
OPTO
Isol ated Feed b ack Inp ut. C onnect to an op ocoup er for an i sol ated p ow er conver er or connect to the
outp ut of a vol ag e- er or am p i er for a noni sol ated p ow er conver er for a feed b ack- er or si g nal
10
10
ILIM
Current-Limit Threshold Input. Connect to the center of a resistor-divider from REF to GND to set
the current-limit threshold voltage.
11
11
SKTOFF
C ur ent- Li m O f- Ti m e Inp ut. C onnect a cap aci or fr om S KTOFF to GN D to set the cur ent- m off- i m e.
P ul S KTO FF to RE F thr oug h a 10k
r esi stor to l atch off the IC after an over cur ent event.
12
12
CS
Current-Sense Input. Provides current-sense feedback for cycle-by-cycle current limit and is
also the current-mode input for the MAX8540. Connect a current-sense resistor from CS to GND.
13
14
13
14
SKTON
GND
Current-Limit On-Time Input. Connect a capacitor to ground to set the current-limit on-time.
Ground
15
15
DRV
Gate Drive for External N-Channel Power MOSFET. Connect to the gate of an external MOSFET
for low-power applications. Connect to the input of an external gate driver for high-power
applications.
16
16
V
CC
Voltage Supply for the IC. Operating input voltage range is 7.6V to 18V. Bypass V
CC
with a
ceramic capacitor to GND.