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MA5003

Major Power Technology Co., Ltd.

Rev.1.3

Dec.01, 2016

Dropout Operation

As the input supply voltage decreases to a value approaching the output voltage, the

duty cycle increases toward the maximum on-time. Further reduction of the supply voltage

forces the high-side switch to remain on for more than one cycle until it reaches 100% duty

cycle.

The output voltage is dropped from the input supply for the voltage which across the

high-side switch.

Setting the Output Voltage

Application circuit item shows the basic application circuit with adjustable output version.

The external resistor sets the output voltage according to the following equation:

Ω

Table 1 Resistor select for output voltage setting

R2

R1

1.0V

150K

100K

1.2V

100K

100K

1.5V

100K

150K

1.8V

100K

200K

2.5V

150K

470K

3.3V

100K

450K

Over Temperature Protection

In most applications the MA5003 does not dissipate much heat due to high efficiency.

But, in applications where the MA5003 is running at high ambient temperature with low

supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the

maximum junction temperature of the part. If the junction temperature reaches

approximately 155°C, the internal high-side power switch will be turned off and the LX node

will become high impedance.

Over Current Protection

The MA5003 cycle-by-cycle limits the peak inductor current to protect embedded

switch from damage. Hence the maximum output current (the average of inductor current) is

also limited. In case the load increases, the inductor current is also increase. Whenever the

current limit level is reached, the output voltage cannot be regulated and starting to drop.

Soft-Start

The MA5003 employs internal soft-start circuitry to reduce supply inrush current during

startup conditions. When the device exits under-voltage lockout or shut-down mode, the

soft-start circuitry will slowly ramp up the output voltage.

Short-circuit Protection

Short-circuit protection will activate once the feedback voltage falls below, and the

operating frequency will be reducing normal switching frequency to reduce power delivered

from input to output.