MP1469 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP1469 Rev. 1.01

www.MonolithicPower.com

10

8/26/2013

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OPERATION

The MP1469 is a high-frequency, synchronous,

rectified, step-down, switch-mode converter

with internal power MOSFETs. It offers a very

compact solution to achieve a 1.5A continuous

output current over a wide input supply range,

with excellent load and line regulation.

The MP1469 operates in a fixed-frequency,

peak-current–control mode to regulate the

output voltage. An internal clock initiates the

PWM cycle to turn on the integrated high-side

power MOSFET. This MOSFET remains on

until its current reaches the value set by the

COMP voltage. When the power switch is off, it

remains off until the next clock cycle starts. If

the current in the power MOSFET does not

reach the COMP set current value within 90%

of one PWM period, the power MOSFET is

forced to turn off.

Internal Regulator

The 5V internal regulator powers most of the

exceeds 5.0V, the regulator output is in full

output decreases.

Error Amplifier

The error amplifier compares the FB voltage

against the internal 0.8V reference (REF) and

outputs a current proportional to the difference

between the two. This output current charges or

discharges the internal compensation network

to form the COMP voltage, which is used to

control the power MOSFET current. The

optimized

internal

compensation

network

minimizes the external component counts and

simplifies the control-loop design.

Enable

EN is a digital control pin that turns the

regulator on and off: Drive EN HIGH to turn on

the regulator, drive it LOW to turn it off. An

internal 1MΩ resistor from EN to GND allows

EN to float to shut down the chip.

The EN pin is clamped internally using a 6.5V

series-Zener-diode as shown in Figure 2.

Connecting the EN input pin through a pullup

EN input current to less than 100μA.

For example, with 12V connected to Vin,

Connecting the EN pin is directly to a voltage

source without any pullup resistor requires

limiting the amplitude of the voltage source to ≤

6V to prevent damage to the Zener diode.

Figure 2: 6.5V Zener Diode Connection

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip

from operating at an insufficient supply voltage.

The MP1469 UVLO comparator monitors the

output voltage of the internal regulator, VCC.

The UVLO rising threshold is about 4.2V while

its falling threshold is consistently 3.86V.

Internal Soft-Start

Soft-start prevents the converter output voltage

from overshooting during startup. When the

chip starts, the internal circuit generates a soft-

start voltage (SS) that ramps up from 0V to

1.2V: When SS falls below the internal

reference (REF), SS overrides REF so that the

error amplifier uses SS as the reference; when

SS exceeds REF, the error amplifier resumes

using REF as its reference. The SS time is

internally set to 1ms.

Over-Current-Protection and Hiccup

The MP1469 has a cycle-by-cycle over-current

limit for when the inductor current peak value

exceeds the set current-limit threshold. First,

when the output voltage drops until FB falls

below

the

Under-Voltage

(UV)

threshold

(typically 200mV) to trigger a UV event, the

MP1469 enters hiccup mode to periodicall

restart the part. This protection mode is

especially useful when the output is dead-

shorted to ground. This greatly reduces the

average short-circuit current to alleviate thermal

issues and to protect the regulator. The

MP1469 exits hiccup mode once the over-

current condition is removed.