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EL7556BCM

Integrated Adjustable 6 Amp Synchronous Switcher

Intersil 

EL7556B

Operating frequency can be adjusted through the COSC pin

or can be driven by an external clock source. If the oscillator

is driven by an external source, care must be taken in the

selection of CSLOPE. Since the COSC and CSLOPE values

determine the open loop gain of the system, changes to

COSC require corresponding changes to CSLOPE in order to

maintain a constant gain ratio. The recommended ratio of

COSC to CSLOPE is 1.5:1

Temperature Sensor

An internal temperature sensor continuously monitors die

temperature. In the event that die temperature exceeds the

thermal trip-point, the OT pin will output a logic 0. The upper

and lower trip points are set to 135°C and 100°C

respectively. To enable thermal shutdown this pin should be

tied directly to OUTEN. Use of this feature is recommended

during normal operation.

Power Good and Power On Reset

During power up the output regulator will be disabled until

VIN reaches a value of approximately 4.0V. Approximately

500mV of hysteresis is present to eliminate noise induced

oscillations.

Under-voltage and over-voltage conditions on the regulator

output are detected through an internal window comparator.

A logic 1 on the PWRGD output indicates that regulated

output voltage is within ±10% of the nominally programmed

output voltage. Although small, the typical values of the

PWRGD threshold will vary with changes to external

feedback (and resultant loop gain) of the system. This

dependence is shown in the typical performance curves.

Thermal Management

The EL7556B utilizes “fused lead” packaging technology in

conjunction with the system board layout to achieve a lower

thermal resistance than typically found in standard 28-pin

SO packages. By fusing (or connecting) multiple external

leads to the die substrate within the package, a very

conductive heat path to the outside of the package is

created. This conductive heat path MUST then be connected

to a heat sinking area on the PCB in order to dissipate heat

out and away from the device. The conductive paths for the

EL7556B package are the fused leads: # 7, 9, 10, 11, 12, 18,

and 19. If a sufficient amount of PCB metal area is

connected to the fused package leads, a junction-to-ambient

thermal resistance of approximately 31°C/W can be

achieved (compared to 78°C/W for a standard SO28

package). The general relationship between PCB heat-

sinking metal area and the thermal resistance for this

package is shown in the Performance Curves section of this

data sheet. It can be readily seen that the thermal resistance

for this package approaches an asymptotic value of

approximately 31°C/W without any airflow. Additional

information can be found in Application Note #8 (Measuring

the Thermal Resistance of Power Surface-Mount Packages).

If the thermal shutdown pin is connected to OUTEN the IC

will enter thermal shutdown when the maximum junction

temperature is reached. For a thermal shutdown of 135°C

and power dissipation of 2.2W the ambient temperature is

limited to a maximum value of 67°C (typical). The ambient

temperature range can be extended with the application of

air flow. For example, the addition of 100LFM reduces the

thermal resistance by approximately 15% and can extend

the operating ambient to 77°C (typical). Since the thermal

performance of the IC is heavily dependent on the board

layout, the system designer should exercise care during the

design phase to ensure that the IC will operate under the

worst-case environmental conditions.

All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.

Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality

Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without

notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and

reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result

from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.

For information regarding Intersil Corporation and its products, see www.intersil.com

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