en5336 Enpirion, en5336 Datasheet - Page 9

• Manufacturer Part Number: en5336
• Description: 3a Voltage Mode Synchronous Buck Pwm Dc-dc Converter With Integrated Inductor External Output Voltage Programming
• Manufacturer: Enpirion

Rev 1.0 November 2006
Over-Current Protection
The current limit function is achieved by sensing
the current flowing through the sense P-
MOSFET. When the sensed current exceeds the
current limit, both NFET and PFET switches are
turned off. If the over-current condition is
removed, the over-current protection circuit will
enable the PWM operation. If the over-current
condition persists, the soft start capacitor will
eventually discharge and cause the converter to
go through a full soft-start cycle. This circuit is
designed to provide high noise immunity.
It is possible to adjust the over-current set point
by connecting a resistor between ROCP (pin 27)
and GND (increase the trip point) or PVIN
(decrease the trip point). The nominal over
current trip point is set to 4.5A. The voltage at the
ROCP pin is designed to be 0.8V.
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 PVIN.
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.
Design Considerations for Lead-Frame Based Modules
Exposed Metal on Bottom Of Package
Lead frame offers many advantages in thermal performance, in reduced electrical lead resistance,
and in overall foot print. However, they do require some special considerations.
In the assembly process lead frame construction requires that, for mechanical support, some of the
lead-frame cantilevers be exposed at the point where wire-bond or internal passives are attached.
This results in several small pads being exposed on the bottom of the package.
©Enpirion 2006 all rights reserved, E&OE
Thermal Overload Protection
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.
Input Under-voltage Lock-out
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.
Compensation
The
through the use of a type 3 compensation
network and is optimized for use with about 47µF
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.
In some cases modifications to the compensation
may be required. For more information, contact
Enpirion Applications Engineering support.
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