MP100 – OFFLINE INDUCTOR-LESS REGULATOR

MP100 Rev. 1.04

www.MonolithicPower.com

8

1/23/2014

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© 2014 MPS. All Rights Reserved.

OPERATION

MP100 employs a smart inductor-less regulator

design (patent pending) to charge the VD

capacitor (C1 in Figure 4) from the offline AC

input, and then to deliver the stored energy to the

load with a stable output voltage. When VIN is

less than its 35V threshold, VD can be charged

up by up to 1.8A input current. An internal LDO

regulates VOUT to 12V and can supply up to

10mA load when VIN is between 85VAC and

305VAC. The proprietary design allows the

universal AC input to efficiently power the IC

directly.

Startup

During the startup, the internal switch connected

between VIN and VB turns on when the input

voltage is within its charging window (typically

below 35V), thus gradually charging the VD

voltage. The LDO will not resume with a soft-

start until the VD voltage reaches 15.3V.

Active Bleeder Circuit

The input voltage may not enter its charging

window during normal operation due to parasitic

capacitance from VIN to GND. An active bleeder

circuit is enabled to pull down the VIN voltage

whenever the VD voltage falls below 14V to

guarantee that the output gets enough energy

from the input ports. In addition, when the power

supply shuts down, the active bleeder circuit

discharges the energy stored in the parasitic

capacitor to ensure that the circuit can restart

easily.

VD Over-Voltage Protection

The VD capacitor provides energy for the output

load. If the voltage of VD exceeds 30V, the

internal switch between VIN and VB turns off

immediately to prevent the VD voltage from rising

too high, which can damage the LDO stage.

Short-Circuit Protection

The output current is limited to 150mA if the

output is shorted to ground, which also

decreases the VD voltage. When VD drops

below 6.8V, LDO turns off. The input voltage then

gradually charges VD up to 15.3V to enable the

LDO. When LDO turns on, the output current

drops the VD voltage to 6.8V again. This process

will continue until the output short condition

ceases.

Over-Current Protection

The

VD

and

VOUT

voltages

will

drop

simultaneously if the output current exceeds its

normal value. When the VD voltage falls to 6.8V,

the second stage LDO shuts down immediately.

Then the input voltage charges VD to 15.3V to

enable the LDO. Due to the output current limit

circuit, the maximum current is typically limited to

150mA.

Thermal Shutdown Protection

Accurate temperature protection prevents the

chip

from

operating

at

exceedingly

high

temperatures. When the silicon die temperature

exceeds 160°C, the whole chip shuts down.

When the temperature falls below its lower

threshold of 140

°C, the chip is enabled again.

Power-Good

The MP100 integrates a power-good circuit to

signal that the output meets the controller IC’s

requirements. It is an open drain structure and

requires a pull-up resistor to VOUT. During start

up, the VOUT voltage rises smoothly. When it

reaches 80% of its normal value, the power-good

signal goes high after a 200µs delay to indicate a

normal output.