MCP1799 datasheet(13/25 Pages) MICROCHIP

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DS20006248A-page 13

MCP1799

4.4

Circuit Protection

The MCP1799 features current limit protection during

an output short circuit event that occurs in normal oper-

ation.

The MCP1799 was tested using the AEC-Q100 test

set-up in Figure 4-2. The testing conditions require the

use of very high parasitic inductances on the input and

output. For cases like this, it is required to prevent the

output voltage going below ground with more than 1V.

Note that the VOUT pin can withstand a maximum of

-0.3VDC (see Absolute Maximum Ratings †). This

can be achieved by placing a Schottky diode with the

cathode to VOUT and anode to ground.

Thermal shutdown functionality is present on the

device and adds to the protection features of the part.

Thermal shutdown gets triggered at typical value of

+180°C and has a typical hysteresis of 22°C.

FIGURE 4-2:

Short Circuit Test Set-Up.

4.5

Dropout Operation

For VR = 5V, MCP1799 can be found operating in a

dropout condition (the minimum input voltage is 4.5V),

which can happen during a cold crank event, when the

supply voltage can drop down to 3V. It is preferred to

make sure that the part does not operate in dropout

during DC operation so that the AC performance is

maintained.

The device has a dropout voltage of approximately

300 mV at full load and room temperature, but because

of the extended temperature range at +150°C, due to

increased leakage at hot, it reaches up to 1100 mV. For

a 5V output, the minimum supply voltage required in

order to have a regulated output, within specification, is

6.2V.

FIGURE 4-3:

Line Step from Dropout.

4.6

Input UVLO

On the rising edge of the VIN input, the internal

architecture adds 550 µs delay before allowing the

regulator output to turn on. After this 550 µs delay, the

regulator starts charging the load capacitor as the

output rises from 0V to its regulated value. The

charging current amplitude will be limited by the short

circuit current value of the device.

The UVLO block helps prevent false start-ups, during

the power-up sequence, until the input voltage reaches

a value of 2.8V. The minimum input voltage required for

normal operation is 4.5V.

4.7

Package and Device

Qualifications

The MCP1799 are AEC-Q100, grade 0 and PPAP

capable. The Grade 0 qualification allows the

MCP1799 to be used within an extended temperature

range, from -40°C to +150°C.

VIN

VOUT

GND

MCP1799

COUT

1 µF

50V

CIN

1 µF

100V

Lshort = 5 µH

Rshort = 10 m

Lshort = 5 µH

Rshort = 100 m

GND

OFF

Ideal

Supply

GND

VIN

200 ms/div

2V/div

VOUT

2V/div

IOUT = 10 mA

11V

VR = 5V

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