EP53A7LQ Datasheet, PDF(13/17 Page) Enpirion, Inc. – 1000mA Synchronous Buck Regulator with Integrated Inductor

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EP53A7LQ Datasheet, PDF (13/17 Pages) Enpirion, Inc. – 1000mA Synchronous Buck Regulator with Integrated Inductor

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down begins. For devices with ENABLE and

LLM tied to VIN, contact Enpirion Applications

engineering for specific recommendations.

Increased output filter capacitance and/or

increased bulk capacitance at the load will

decrease the magnitude of the LLM ripple.

Refer to the section on output filter capacitance

for maximum values of output filter capacitance

and the Soft-Start section for maximum bulk

capacitance at the load.

NOTE: For proper LLM operation the

EP53A7xQI requires a minimum difference

between VIN and VOUT of 700mV. If this

condition is not met, the device cannot be

assured proper LLM operation.

NOTE: Automatic LLM/PWM is not available

when using the external resistor divider option

for VOUT programming.

Soft Start

Internal soft start circuits limit in-rush current

when the device starts up from a power down

condition or when the âENABLEâ pin is

asserted âhighâ. Digital control circuitry limits

the VOUT ramp rate to levels that are safe for

the Power MOSFETS and the integrated

inductor.

The EP53A7HQI has a soft-start slew rate that

is twice that of the EP53A7LQI.

When the EP53A7LUI is configured in external

resistor divider mode, the device has a fixed

VOUT ramp time. Therefore, the ramp rate will

vary with the output voltage setting. Output

voltage ramp time is given in the Electrical

Characteristics Table.

Excess bulk capacitance on the output of the

device can cause an over-current condition at

startup. The maximum total capacitance on

the output, including the output filter capacitor

and bulk and decoupling capacitance, at the

load, is given as:

EP53A7LQI:

COUT_TOTAL_MAX = COUT_Filter + COUT_BULK = 200uF

EP53A7HQI:

COUT_TOTAL_MAX = COUT_Filter + COUT_BULK = 100uF

EP53A7LQI/EP53A7HQI

EP53A7LUI in external divider mode:

COUT_TOTAL_MAX = 2.25x10-4/VOUT Farads

The nominal value for COUT is 10uF. See the

applications section for more details.

Over Current/Short Circuit Protection

The current limit function is achieved by

sensing the current flowing through a sense P-

MOSFET which is compared to a reference

current. When this level is exceeded the P-

FET is turned off and the N-FET is turned on,

pulling VOUT low. This condition is maintained

for approximately 0.5mS and then a normal

soft start is initiated. If the over current

condition still persists, this cycle will repeat.

Under Voltage Lockout

During initial power up, an under voltage

lockout circuit will hold-off the switching

circuitry until the input voltage reaches a

sufficient level to insure proper operation. If

the voltage drops below the UVLO threshold,

the lockout circuitry will again disable the

switching. Hysteresis is included to prevent

chattering between states.

Enable

The ENABLE pin provides a means to shut

down the converter or enable normal

operation. A logic low will disable the

converter and cause it to shut down. A logic

high will enable the converter into normal

operation.

NOTE: The ENABLE pin must not be left

floating.

Thermal Shutdown

When excessive power is dissipated in the

chip, the junction temperature rises. Once the

junction temperature exceeds the thermal

shutdown temperature, the thermal shutdown

circuit turns off the converter output voltage

thus allowing the device to cool. When the

junction temperature decreases by 25CÂ°, the

device will go through the normal startup

process.

01543

11/11/2009

www.enpirion.com

Rev:B

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