MCP19035-AAAAESLASHMF datasheet(15/44 Pages) MICROCHIP

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DS22326B-page 15

MCP19035

4.8

Internal Voltage Regulator (LDO)

The MCP19035 controller offers an internal 5V Low

Dropout Voltage Regulator. This regulator provides the

bias voltage for all internal circuits. A ceramic capacitor

(4.7 μF minimum) must be connected between the

output of this LDO (VCC pin) and ground (GND pin) for

stable operation.

An external low noise load may be powered from this

regulator, but the total current consumed from the LDO

output (internal circuitry of MCP19035 + external load)

should not exceed 50 mA. The internal circuitry of the

MCP19035 consume approximately 5 mA. The total

amount of current available to power the external load

can be estimated from Equation 4-1:

EQUATION 4-1:

This LDO dissipates power within the MCP19035. To

avoid tripping the Overtemperature Protection Circuit,

the designer must ensure that the maximum die

temperature is below +125°C under worst case

conditions (i.e. high input voltage). For further

information regarding the maximum dissipated power

for LDOs, see Microchip’s AN761 and AN792

application notes.

The LDO is protected against overload and short-circuit

conditions. Consistent performance of the internal

MOS drivers is ensured by monitoring the LDO output

voltage; if the voltage is lower than 3.3V typical, the

chip will enter in Shut-Down mode to prevent damage

to the external MOSFETs.

4.9

Internal MOSFET Drivers

Internal MOSFET drivers are capable of driving

external, “Logic Level” (+5V) MOSFETs.

The Low-Side Driver (LDRV) is referenced to the GND

pin and is capable of sourcing 1A and sinking 1.5A.

The High-Side Driver (HDRV) is floating and capable of

sourcing and sinking 1A. This driver is powered from an

external bootstrap capacitor.

The drivers have non-overlapping timing that is

governed by an adaptive delay circuit to minimize body

diode conduction in the synchronous rectifier.

For the optimized Dead Time version of the

MCP19035, the adaptive delay circuit is disabled and

the Dead Time has a fixed value.

4.10

Overcurrent Protection

Overcurrent protection is accomplished by monitoring

the voltage across the external MOSFETs when they

are ON (conducting).

For the high-side overcurrent protection, when the

sensed voltage drop across the high-side MOSFET is

greater than the high-side overcurrent threshold

voltage, the high-side MOSFET is immediately turned

off

and the high-side

overcurrent counter

incremented by one. On the next cycle, if the high-side

overcurrent threshold voltage is not exceeded, the

high-side overcurrent counter is decreased by one

count. If the high-side overcurrent counter reaches a

count of 7, a fault condition exists and the MCP19035

turns off both external MOSFETs.

After a 60 ms delay, the MCP19035 will attempt to

restart. If during the next cycle, a high-side overcurrent

threshold voltage is measured across the high-side

MOSFET, a fault is again declared and both external

MOSFETs are turned off for another 60 ms. However, if

after the attempted restart a high-side overcurrent

threshold voltage is not measured across the high-side

MOSFET, the high-side overcurrent counter is

decreased by one and the MCP19035 continues to

operate until the high-side overcurrent counter reaches

a count of 7.

The low-side overcurrent protection behaves much the

same way as the high-side overcurrent protection. The

difference is that the low-side MOSFET is not

immediately turned off when a low-side overcurrent

threshold voltage is measured. It remains on until the

next cycle begins.

IExternal Load = 50 mA - fSW x(QG(High Side) + QG(Low Side)) - 5 mA

Where:

IExternal Load = Current Available for powering the

External Load

fSW = Switching Frequency (300 kHz or

600 kHz)

QG(High Side) = Total Gate Charge of the High-Side

MOSFET at 4.5V VGS

QG(Low Side) = Total Gate Charge of the Low-Side

MOSFET at 4.5V VGS

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