MP2467 – 2.5A, 36V, 500kHz STEP-DOWN CONVERTER
MP2467 Rev. 1.11 www.MonolithicPower.com 8
1/24/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
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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