MP1499 – 16V/5A PEAK SYNCHRONOUS STEP-DOWN CONVERTER

MP1499 Rev. 1.0

www.MonolithicPower.com

12

7/26/2012

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2012 MPS. All Rights Reserved.

exceeds the set current limit threshold.

Meanwhile, output voltage starts to drop until

FB is below the Under-Voltage (UV) threshold,

typically 50% below the reference. Once a UV

is triggered, the MP1499 enters hiccup mode to

periodically restart the part. This protection

mode is especially useful when the output is

dead-short to ground. The average short circuit

current is greatly reduced to alleviate the

thermal issue and to protect the regulator. The

MP1499 exits the hiccup mode once the over

current condition is removed.

Thermal Shutdown

Thermal shutdown is implemented to prevent

the chip from operating at exceedingly high

temperatures. When the silicon die temperature

is higher than 150°C, it shuts down the whole

chip. When the temperature is lower than its

lower threshold, typically 130°C, the chip is

enabled again.

Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered

by an external bootstrap capacitor. This floating

driver has its own UVLO protection. This

UVLO’s rising threshold is 2.2V with a

hysteresis of 150mV. The bootstrap capacitor

more than 5V, U1 will regulate M1 to maintain a

5V BST voltage across C4. A 10Ω resistor

placed between SW and BST cap is strongly

recommended to reduce SW spike voltage.

R4

Figure 6—Internal Bootstrap Charging

Circuit

Startup and Shutdown

If both VIN and EN are higher than their

appropriate thresholds, the chip starts. The

reference block starts first, generating stable

reference voltage and currents, and then the

internal regulator is enabled. The regulator

provides stable supply for the remaining

circuitries.

Three events can shut down the chip: EN low,

VIN low and thermal shutdown. In the shutdown

procedure, the signaling path is first blocked to

avoid any fault triggering. The COMP voltage

and the internal supply rail are then pulled

down. The floating driver is not subject to this

shutdown command.