MPQ2918GL datasheet(21/32 Pages) MPS

21 / 32 page

MPQ2918 – 4V - 40V, CURRENT MODE, SYNC, STEP-DOWN CONTROLLER

MPQ2918 Rev. 1.01

www.MonolithicPower.com

8/17/2017

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

EN/SYNC Control

The MPQ2918 has a dedicated enable

(EN/SYNC) control that uses a bandgap-

generated precision threshold of 1.22V. By

pulling EN/SYNC high or low, the IC can be

enabled or disabled. To disable the part,

EN/SYNC must be pulled low for at least 40µs.

Tie EN/SYNC to VIN through a resistor divider

(R16 and R17) to program the VIN start-up

threshold (see Figure 4). The EN/SYNC

threshold is 1.09V (falling edge), so the VIN

UVLO threshold is 1.09V x (1 + R16/R17).

Otherwise, if VIN ≤ 52V, EN/SYNC can be

connected to VIN directly. If VIN ≥ 52V, a ≥50kΩ

pull-up resistor is needed to prevent EN/SYNC

from breaking down.

Figure 4: EN/SYNC Resistor Divider

Synchronize

The MPQ2918 can be synchronized to an

external clock ranging from 100kHz up to

1000kHz through EN/SYNC. The internal clock

rising edge is synchronized to the external clock

rising edge. The pulse width (both on and off) of

the external clock signal should be no less than

100ns.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented

to protect the chip from operating at an

insufficient input supply voltage. The MPQ2918

UVLO rising threshold is about 4.5V, while its

falling threshold is a consistent 3.7V.

Thermal Protection

Thermal protection prevents damage to the IC

from

excessive

temperatures.

The

die

temperature is monitored internally until the

thermal limit is reached. When the silicon die

temperature is higher than 170°C, the entire

chip shuts down. When the temperature is

lower than its lower threshold (typically 20°C),

the chip is enabled again.

Start-Up and Shutdown

If both VIN and EN/SYNC are higher than their

respective thresholds, the chip starts up. The

reference block starts first, generating stable

reference voltages and currents. The internal

regulator is then enabled. The regulator

provides a stable supply for the remaining

circuitries.

Three events can shut down the chip:

EN/SYNC low, VIN low, and thermal shutdown.

During the shutdown procedure, the signal path

is blocked first to avoid any fault triggering.

VCOMP and the internal supply rail are then

pulled down. The floating driver is not subject to

this shutdown command.

Pre-Bias Start-Up

If SS is less than FB at start-up, the output has

a pre-bias voltage, and neither TG nor BG is

turned on until SS is greater than FB.

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