MP103 Rev. 1.01

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1/23/2014

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[t4, t5]: At the time of t4, VIN falls to the slow

turn-on threshold; the driver current begins to

slowly rise to turn on the external BJT, at the

time of t5, the external BJT is fully on;

[t5, t6]: As VIN falls, the charging current is

decreased, and the VB voltage is increased by

the charge current. At the time of t6, VIN falls to

the value equal to VB voltage, there is no

current flowing into VB capacitor;

[t6, t1]: During this period, although the driver is

active, since VIN is lower than VB voltage, so

there is no charging current, the VB capacitor

provide the power for the output load and the

voltage drop from v4 to v1 at the time of t1;

Adaptive Active Charging Window

To minimize the power loss of BJT and LDO,

MP103 integrates an adaptive active charging

window control, which maintain the maximum

voltage difference between VB and VOUT stay

at a constant level, thus the VB peak voltage is

limited related to VOUT.

When VIN varies from high to low voltage into

its charging window and the VB voltage is lower

will be turned on and VB capacitor will be

charged up. If VB voltage is charged up to its

output voltage, then the driver will be slowly

turned off although VIN doesn’t reach its slow

turn-off threshold.

Figure 4 depicts the situation that VB reaches

its peak limit when VIN is in its charging window.

0

VIN

IDR

IIN

t1 t2

t4 t5

t

t

t

0

0

t3

t6

VB

Figure 4: Adaptive Active Charging Window

Active Bleeder Circuit

Due to the parasitic capacitor of VIN to GND,

the input voltage may not fall into its charging

window during normal operation.

At start up, the active bleeder is always on to

pull down the input voltage into its charging

window to charge VB capacitor to its output

LDO is enabled.

During steady state mode, to guarantee the

output get enough energy from input ports,

active bleeder circuit is enabled whenever the

Besides, when the power supply is shut down,

active bleeder circuit discharges the energy

stored in parasitic capacitor to ensure the circuit

can restart easily.

Short Circuit Protection

if the output is shorted to ground, which also

decreases the VB voltage. When VB drops

input voltage then gradually charges VB up to

LDO turns on, the output current drops the VB

voltage to 7.6V again. This process will

continue until the output short condition ceases.

Over Load Protection

The VB and VOUT voltages will drop

simultaneously if the output current exceeds its

normal value. When the VB voltage falls to 7.6V

immediately. Then the input voltage charges VB

the output current limit circuit, the maximum

VB Short to GND Protection

When VB is shorted to GND, the driver current

decrease the power consumption of external

BJT, thus the thermal damage of external BJT

is prevented.

Over Temperature Protection

An NTC resistor in series with a regular resistor

can be connected between RT and GND for