Rev 1.2 October 2008
EN5335QI
point by about 50% by connecting a 7.5k
Ω
Input Under-voltage Lock-out
resistor between ROCP (pin 27) and GND. The
typical voltage at the ROCP pin is 0.75V.
Circuitry is provided to ensure that when the
input voltage is below the specified voltage
range, the converter will not start-up. Circuits for
hysteresis, input de-glitch and output leading
edge blanking are included to ensure high noise
immunity and prevent false tripping.
In some cases, such as the start-up of FPGA
devices, it is desirable to blank the over-current
protection feature. In order to disable over-
current protection, the ROCP pin should be tied
to any voltage between 2.5V and PVIN.
Compensation
The EN5335QI is internally compensated
through the use of a type 3 compensation
network and is optimized for use with about 50ꢀF
of output capacitance and will provide excellent
loop bandwidth and transient performance for
most applications. (See the section on Capacitor
Selection for details on recommended capacitor
types.) Voltage mode operation provides high
noise immunity at light load.
Over-Voltage Protection
When the output voltage exceeds 120% of the
programmed output voltage, the PWM operation
stops, the lower N-MOSFET is turned on and the
POK signal goes low. When the output voltage
drops below 95% of the programmed output
voltage, normal PWM operation resumes and
POK returns to its high state.
Thermal Overload Protection
In some cases modifications to the compensation
may be required. For more information, contact
Enpirion Applications Engineering support.
Thermal shutdown will disable operation once
the Junction temperature exceeds approximately
150ºC. Once the junction temperature drops by
approx 25ºC, the converter will re-start with a
normal soft-start.
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