MP2229 – 21V, 6A SYNCHRONOUS STEP-DOWN CONVERTER

MP2229 Rev. 1.0

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13

2/12/2015

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internal clock rising edge is synchronized to the

external clock rising edge.

Low-Power Mode (LPM)

The MP2229 has a low-power mode for light

reaches the value set by the COMP voltage.

clock is blocked. Thus, the MP2229 skips

pulses for pulse frequency modulation (PFM)

mode, achieving the light-load power save (see

Figure 4).

FIGURE 4. Simplified LPM Control Logic

To enable low-power mode, connect LPM to

VCC or to a voltage divider from VCC. When

power mode, connect LPM to ground, and the

converter operates constantly in fixed frequency

CCM.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip

from operating at an insufficient supply voltage.

The MP2229 UVLO comparator monitors the

output voltage of the internal regulator (VCC).

The UVLO rising threshold is 4.1V while its

falling threshold is 3.5V.

External Soft-Start (SS)

Connect a capacitor from SS to ground to

adjust the soft-start time. When the soft-start

begins, an internal 10μA current source

charges the external capacitor. The soft-start

capacitor connects to the non-inverting input of

the error amplifier. The soft-start period lasts

until the voltage on the soft-start capacitor

exceeds the 0.6V reference. At this point, the

reference voltage takes over at the non-

inverting error-amplifier input. The soft-start

time can be calculated as follows:

SS

SS

0.6V C (nF)

t(ms)

10 A

×

=

μ

Pre-Bias Start-Up

The MP2229 has been designed for a

monotonic start-up into pre-biased loads. If the

output is pre-biased to a certain voltage during

BST voltage exceeds its rising threshold

voltage, then the soft-start capacitor is charged.

When the soft-start capacitor voltage exceeds

the sensed output voltage at FB, the part starts

to operate normally.

Over-Current Protection (OCP)

The MP2229 has a cycle-by-cycle over-current

limit, which limits the inductor current in case of

an output over load or short circuit. If the over

load or short circuit lasts for an extended period,

the FB voltage can drop below the under-

voltage (UV) threshold (40% of the reference,

typically). Once a UV is triggered, the MP2229

enters hiccup mode to re-start the part

periodically. This protection mode is 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 MP2229 exits hiccup mode once

the over-current condition is removed.

Thermal Shutdown (TSD)

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the die temperature reaches 150°C, it

shuts down the whole chip. When the

temperature falls below its lower threshold

(120°C, typically), the chip is enabled again.

Floating Driver and Bootstrap Charging

An external bootstrap capacitor powers the

floating power MOSFET driver. This floating

driver has its own UVLO protection. The

UVLO’s rising threshold is 2.03V with a

hysteresis of 200mV. The bootstrap capacitor

a 5V BST voltage across C5. A 10Ω resistor