Rev 1.0 – July 2005

www.enpirion.com

9

EN5360

Power Up Sequencing

The sequencing of AVIN, PVIN and ENABLE should

meet the following requirements:

1. ENABLE should not be asserted before PVIN.

2. PVIN should not be applied before AVIN.

Note that tying AVIN, PVIN and ENABLE together

and brought up at the same time does meet these

requirements.

POK Operation

The POK signal is an open drain signal from the

converter indicating the output voltage is within the

specified range. The POK signal will be a logic high

when the output voltage is within 90% - 120% of the

programmed output voltage. If the output voltage goes

outside of this range, the POK signal will be a logic

low until the output voltage has returned to within this

range. In the event of an over-voltage condition the

POK signal will go low and will remain in this

condition until the output voltage has dropped to 95%

of the programmed output voltage before returning to

the high state (see also Over Voltage Protection)

Over-Current Protection

The cycle-by-cycle current limit function is achieved

by sensing the current flowing through the sense P-

MOSFET and a signal generated by a differential

amplifier with a preset over-current threshold. During

a particular cycle, if the over-current threshold is

exceeded, the power P-MOSFET is turned off and the

power N-MOSFET is turned on to protect the P-

MOSFET. If the over-current condition is removed,

the over-current protection circuit will enable the

PWM operation. If the over-current condition persists,

the converter will eventually go through a full soft-

start cycle. This circuit is designed to provide high

noise immunity.

It is possible to raise the over-current set-point by

~50% by connecting a 4.99k

Ω resistor between ROCP

and GND.

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

Thermal shutdown will disable operation once the

Junction temperature exceeds approximately 160ºC.

Once the junction temperature drops by approx 25ºC,

the converter will re-start with a normal soft-start.

Input Under-voltage Operation

Circuitry is provided to ensure that when the input

voltage is below the specified voltage range, the

operation of the converter is controlled and

predictable. Circuits for hysteresis, input de-glitch and

output leading edge blanking are included to ensure

high noise immunity and prevent false tripping.

Compensation

The EN5360 is internally compensated through the

use of a type 3 compensation network and is

optimized for use with about 50µF 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.) In some cases

modifications to the compensation may be required.

For more information, contact Enpirion Applications

Engineering support.

Layout Considerations

The EN5360 Layout Guidelines application note

provides more details on specific layout

recommendations for this part. The following are

general layout guidelines to consider.

The CMOS chip inside the EN5360 has two grounds:

AGND for the controller, and PGND for the power

stage. These two grounds need to be connected

outside the package at one point through a low-

impedance trace. The connection should be made such

that the impedance between the connection point and

the AGND pad on the package is minimized. Since

the internal voltage sensing circuit is based on AGND,

the connection of the two grounds should also be

made such that the best voltage regulation can be

achieved. The soft-start capacitor, the voltage

programming resistors, and any other external control

component should be tied to AGND.

The placement of the input decoupling capacitors and