MP2499M – 36V, 3A MAX, SYNCHRONOUS BUCK CONVERTER

MP2499M Rev 1.0

www.MonolithicPower.com

12

5/1/2018

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© 2018 MPS. All Rights Reserved.

This current flows through the feedback resistor

(R1) and generates the compensation voltage

MP2499M

FB

GND

SW

L

+

R1

R2

Co

Rsense

+

-

Figure 3: Output Line Drop Compensation

COMP

LOAD

SENSE

R1

V

I

R

1

16.5k













(2)

The line drop compensation voltage amplitude

increases linearly as the load current increases.

Setting a different R1 value can produce

different voltages to compensate for the cable

drop voltage (see Figure 4). When the load

current is 2.4A, R1 is 82.5k

and the compensation voltage is 384mV.

Figure 4: Output Line Drop Compensation at

Different R1 Values

Over-Current Protection (OCP) and Hiccup

The MP2499M uses a cycle-by-cycle over-

current limit when the inductor current peak

value exceeds the current limit threshold. If the

output voltage drops until FB is below the

under-voltage (UV) threshold (typically 30%

below the reference), the MP2499M enters

hiccup mode to restart the part periodically.

This protection mode is especially useful when

the output is dead-shorted to ground. The

average short-circuit current is reduced greatly

to alleviate thermal issues and protect the

regulator. The MP2499M exits hiccup mode

once the over-current condition is removed.

The MP2499M also has a continuous output

current limit. A current sensing resistor senses

the load current to protect the output from over-

current.

If output over-current is detected

(ISENSE voltage exceeds 118mV), and the

output voltage drops until FB is 30% below the

reference, the MP2499M enters hiccup mode.

The MP2499M enters hiccup mode when the

soft start finishes, over-current occurs (internal

cycle-by-cycle inductor peak current limit or

external sensed continuous output current limit),

and FB falls below the UV threshold.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die temperature exceeds

170°C, the entire chip shuts down. When the

temperature drops below its lower threshold

(typically 140°C), the chip is enabled again.

Floating Driver and Bootstrap Charging

An external bootstrap capacitor powers the

floating power MOSFET driver. A dedicated

internal regulator charges and regulates the

bootstrap capacitor voltage to ~5V (see Figure

5). When the voltage between the BST and SW

nodes drops below regulation, a PMOS pass

SW. The external circuit should provide enough

voltage headroom to facilitate charging. As long

bootstrap capacitor remains charged.

bootstrap capacitor cannot charge. When the

reaches its maximum for fast charging. When

bootstrap capacitor. The floating driver has its

own UVLO protection with a rising threshold of

2.2V and hysteresis of 150mV. A 20Ω resistor

placed between the SW and BST capacitor is

strongly recommended to reduce SW voltage

spikes.