MP1660

– SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP86953 Rev. 1.0

www.MonolithicPower.com

11

6/9/2020

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Over-Current Protection (OCP) and Short-

Circuit Protection (SCP)

The MP1660 offers valley current limit control.

While the LS-FET is on, the inductor current is

monitored. When the sensed inductor current

reaches the valley current limit, the low-side

limit comparator turns over. The device enters

over-current protection (OCP) mode, and the

HS-FET waits until the valley current limit

disappears before turning on again. Meanwhile,

the output voltage drops until VFB drops below

the under-voltage (UV) threshold (typically 75%

below the reference). Once UV is triggered, the

MP1660 enters hiccup mode to periodically

restart the part.

During

over-current

protection

(OCP),

the

device attempts to recover from an over-current

fault with hiccup mode. The chip disables the

output power stage, discharges soft start, and

attempts to soft start again automatically. If the

over-current condition still remains after soft

start ends, the device repeats this operation

cycle until the over-current condition is removed

and the output rises back to the regulation level.

OCP is a non-latch protection.

SCP performance is the same as OCP.

Pre-Biased Start-Up

The MP1660 is designed for monotonic start-up

into pre-biased loads. If the output is pre-biased

to a certain voltage during start-up, the BST

voltage is refreshed and charged, and the soft

start voltage is charged as well. If the BST

voltage exceeds its rising threshold voltage and

the soft-start voltage exceeds the sensed

output voltage at FB, the MP1660 begins

working normally.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die temperature exceeds

150°C, the entire chip shuts down. When the

temperature falls below its lower threshold

(typically 130°C), 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

under-voltage

lockout

(UVLO) protection with a rising threshold of

2.2V and a hysteresis of 150mV. VIN regulates

the

bootstrap

capacitor

voltage

internally

through D1, M1, C3, L1, and C2 (see Figure 3).

If VIN - VSW exceeds 3.3V, U2 regulates M1 to

maintain a 3.3V BST voltage across C3.

U1

3.3V

D1

M1

U2

C3

L1

C2

VIN

VOUT

SW

GND

BST

Figure 3: Internal Bootstrap Charger

Start-Up and Shutdown Circuit

If both VIN and EN exceed their respective

thresholds, the chip starts up. The reference

block starts first, generating a stable reference

voltage and current, and then the internal

regulator is enabled. The regulator provides a

stable supply for the remaining circuits.

Three events can shut down the chip: EN going

low, VIN going low, and thermal shutdown. The

shutdown procedure starts by blocking the

signaling

path

initially

to

avoid

any

fault

triggering. The internal supply rail is then pulled

down.