ncp1080 ON Semiconductor, ncp1080 Datasheet - Page 13

• Manufacturer Part Number: ncp1080
• Description: Integrated Poe-pd & Dc-dc Converter Controller
• Manufacturer: ON Semiconductor

senses the current flowing in the external MOSFET for
current mode control and cycle−by−cycle current limit. This
is performed by the current limit comparator which, on the
CS pin, senses the voltage across the external Rcs resistor
located between the source of the MOSFET and the ARTN
pin.
CS pin which ensures that the current limit and PWM
comparators are not prematurely trigged by the current spike
that occurs when the switching MOSFET turns on.
problems that exist with converters running in continuous
Current Limit Comparator
Slope Compensation Circuitry
The NCP1080 current limit block behind the CS pin
The NCP1080 also provides a blanking time function on
To overcome sub−harmonic oscillations and instability
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conduction mode (CCM) and when the duty cycle is close
or above 50 percent, the NCP1080 integrates a current slope
compensation circuit. The amplitude of the added slope
compensation is typically 110 mV over one cycle.
250 kHz, the internal slope provided by the NCP1080 is
27.5 mV/ mA typically.
inserted between OSC and ARTN, and is defined by the
following equation:
The duty cycle limit is fixed internally at 80 percent.
DC−DC Controller Oscillator
As an example, for an operating switching frequency of
The frequency is configured with the Rosc resistor
R
OSC
(kW) +
F
OSC
38600
(kHz)