MP28248GD datasheet(14/19 Pages) MPS

14 / 19 page

MP28248 – 3A, 3.3V-20V INPUT, FAST TRANSIENT SYNCHRONOUS STEP-DOWN CONVERTER IN 2X3MM QFN

MP28248 Rev. 1.0

www.MonolithicPower.com

1/5/2012

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.



 





 SS

REF

tms

CnF

(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

1.92

2.74

3.96

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.

MP28248GD 数据表(PDF) 14 Page - Monolithic Power Systems

MP28248GD 数据表(HTML) 14 Page - Monolithic Power Systems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

数据表下载