MP1469 datasheet(11/17 Pages) MPS

11 / 17 page

MP1469 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP1469 Rev. 1.01

www.MonolithicPower.com

8/26/2013

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

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die temperature exceeds

150°C, it shuts down the whole chip. 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 UVLO protection, with a

rising threshold of 2.2V and a hysteresis of

150mV. VIN regulates the bootstrap capacitor

voltage internally through D1, M1, R4, C4, L1

and C2 (Figure 3). If (VIN-VSW) exceeds 5V,U2

will regulate M1 to maintain a 5V BST voltage

across C4.

VIN

VOUT

Figure 3: Internal Bootstrap Charging

Startup and Shutdown Circuit

If both VIN and EN exceed 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 a stable supply

for the remaining circuits.

Three events can shut down the chip: EN low,

VIN low, and thermal shutdown. In the shutdown

procedure starts by initially blocking the

signaling path 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.

AAM Operation

The

MP1469

has

AAM

(Advanced

Asynchronous Modulation) power save mode

for light load. The AAM voltage is set at 0.5V

internally. Under the heavy load condition, the

VCOMP is higher than VAAM. When clock goes

high, the high-side power MOSFET turns on

and remains on until VILsense reaches the value

set by the COMP voltage. The internal clock

resets every time when VCOMP is higher than

VAAM.

Under the light load condition, the value of

VCOMP is low. When VCOMP is less than VAAM and

VFB is less than VREF, VCOMP ramps up until it

exceeds VAAM, during this time, the internal

clock is blocked, thus the MP1469 skips some

pulses for PFM (Pulse Frequency Modulation)

mode and achieves the light load power save.

VAAM

Clock

VOUT

1.2pF

47pF 500k

20k

VREF

VFB

VIL sense

VCOMP

HS_driver

Figure 4—Simplified AAM Control Logic

When the load current is light, the inductor peak

current is set internally which is about 340mA

for VIN=12V, VOUT=3.3V, and L=6.5μH.The

curve of inductor peak current vs. inductor is

shown in Figure 5.

Inductor Peak Current

vs. Inductor

0.2

0.4

0.6

0.8

1.2

2345

Figure5—Inductor Peak Current vs. Inductor

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