MP2467 – 2.5A, 36V, 500KHz STEP-DOWN CONVERTER

MP2467 Rev. 1.1

www.MonolithicPower.com

8

1/25/2010

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Error Amplifier

The error amplifier compares the FB pin voltage

with the internal reference (REF) and outputs a

current proportional to the difference between

the two. This output current is then used to

charge or discharge the external compensation

network to form the COMP voltage, which is

used to control the power MOSFET current.

During operation, the minimum COMP voltage

is clamped to 0.9V and its maximum is clamped

to 2.0V. COMP is internally pulled down to GND

in shutdown mode. COMP should not be pulled

above 2.6V.

Internal Regulator

Most of the internal circuitries are powered from

the 2.6V internal regulator. This regulator takes

the VIN input and operates in the full VIN range.

When VIN is greater than 3.0V, the output of

the regulator is in full regulation. When VIN is

lower than 3.0V, the output decreases.

Enable Control

The MP2467 has a dedicated enable control pin

(EN). With high enough input voltage, the chip

can be enabled and disabled by EN. Its falling

threshold is 1.2V, and its rising threshold is

1.5V (300mV higher).

If left open, EN is pulled up to about 3.0V by an

internal 1µA current source. To disable the part,

EN pin must be pulled down with greater than

2µA current.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented

to protect the chip from operating at insufficient

supply voltage. The UVLO rising threshold is

about 3.0V while its falling threshold is a

consistent 2.6V.

Internal Soft-Start

The soft-start is implemented to prevent the

converter output voltage from overshooting

during startup. When the chip starts, the

internal circuitry generates a soft-start voltage

(SS) ramping up from 0V to 2.6V. When it is

lower than the internal reference (REF), SS

overrides REF so the error amplifier uses SS as

the reference. When SS is higher than REF,

REF regains control.

Thermal Shutdown

Thermal shutdown is implemented to prevent

the chip from operating at exceedingly high

temperatures. When the silicon die temperature

is higher than its upper threshold, it shuts down

the whole chip. When the temperature is lower

than its lower threshold, the chip is enabled

again.

Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered

by an external bootstrap capacitor. This floating

driver has its own UVLO protection. This

UVLO’s rising threshold is 2.2V with a

hysteresis of 150mV.

At higher duty cycle operation condition, the

time period available to the bootstrap charging

may be too short to sufficiently recharge the

bootstrap capacitor.

In case the internal circuit does not have

sufficient voltage and the bootstrap capacitor is

not charged, extra external circuitry can be

used to ensure the bootstrap voltage is in the

normal operational region.

The DC quiescent current of the floating driver

is about 20µA. Make sure the bleeding current

at the SW node is higher than this value, such

that:

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