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MP28248 Datasheet(PDF) 14 Page - Monolithic Power Systems

Part No. MP28248
Description  High-Efficiency, Fast-Transient, 3A, 4.2V-20V Input Synchronous Step-down Converter in a QFN12 (2x3mm) Package
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Maker  MPS [Monolithic Power Systems]
Homepage  http://www.monolithicpower.com
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MP28248 Datasheet(HTML) 14 Page - Monolithic Power Systems

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MP28248 – 3A, 3.3V-20V INPUT, FAST TRANSIENT SYNCHRONOUS STEP-DOWN CONVERTER IN 2X3MM QFN
MP28248 Rev. 1.0
www.MonolithicPower.com
14
1/5/2012
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.

 
 


SS
SS
SS
REF
tms
I
A
CnF
VV
(11)
If the output capacitors are large, avoid setting a
short SS time to avoid hitting the current limit
during SS. Table 1 lists SS times with different
external capacitor value.
Table 1: Soft-Start Time vs. Capacitor Value
tSS(ms)
CSS(nF)
0.58
10
1.92
33
2.74
47
3.96
68
5.82
100
Over-Current Protection and Short-Circuit
Protection
The MP28248 has cycle-by-cycle over-current
limit control that monitors the inductor current
during the HS-FET ON state. Once the inductor
current exceeds the current limit, the HS-FET
turns off. At the same time, the OCP timer—set
at 50µs—starts. OCP will trigger if the current
reaches or exceeds the current limit every cycle
during those 50µs, and the MP28248 enters
hiccup mode to periodically restart the part.
If VFB < 0.5xVREF and the current hits its limit, the
MP28248 triggers the short-circuit protection
(SCP) immediately and the MP28248 enters
hiccup mode to periodically restart the part.
If VFB < 0.5xVREF and the inductor current peak
value exceeds the set current limit threshold,
MP28248 enters hiccup mode to periodically
restart the part. This protection mode is
especially useful when the output shorts to
ground, greatly reducing the average short-circuit
current and any thermal build-up to protect the
regulator. The MP28248 exits the hiccup mode
once the over current condition is removed.
Over-Voltage Protection (OVP)
MP28248 monitors the output voltage through
the tap of a resistor divider connected to FB.
When VFB exceeds 1.25xVREF, MP28248 triggers
OVP. LS-FET is then left on, while the HS-FET is
off. Exiting OVP requires power cycling the
MP28248.
UVLO protection
MP28248 has UVLO protection. When VIN
exceeds the UVLO rising threshold voltage, the
chip powers up. It shuts off when VIN is less than
the UVLO falling threshold voltage. This is non-
latch protection.
Thermal Shutdown
The junction temperature of the IC is monitored
internally. If the junction temperature exceeds the
threshold value (typically 150°C), the converter
shuts off. This is non-latch protection. There is
about 25°C hysteresis. Once the junction
temperature drops to around 125°C, it initiates a
soft start.


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