MP1410 データシートの表示（PDF） - Monolithic Power Systems

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MP1410

2A Step-Down Switch-Mode Regulator

Monolithic Power Systems 

Monolithic Power Systems

Functional Description

The MP1410 is a current-mode step-down

switch-mode regulator. It regulates input

voltages from 4.75V to 15V down to an output

voltage as low as 1.22V, and is able to supply

up to 2A of load current.

The MP1410 uses current-mode control to

regulate the output voltage. The output

voltage is measured at FB through a resistive

voltage divider and amplified through the

internal error amplifier. The output current of

the transconductance error amplifier is

presented at COMP where a network

compensates the regulation control system.

The voltage at COMP is compared to the

switch current measured internally to control

the output voltage.

The converter uses an internal n-channel

MOSFET switch to step-down the input

voltage to the regulated output voltage. Since

the MOSFET requires a gate voltage greater

than the input voltage, a boost capacitor

connected between SW and BS drives the

gate. The capacitor is internally charged while

the switch is off. An internal 10Ω switch from

SW to GND is used to insure that SW is pulled

to GND when the switch is off to fully charge

the BS capacitor.

Application Information

Setting the Output Voltage

The output voltage is set using a resistive

voltage divider from the output voltage to FB.

The voltage divider divides the output voltage

down by the ratio:

VFB = VOUT * R2 / (R1 + R2).

Thus the output voltage is:

VOUT = 1.222 * (R1 + R2) / R2.

MP1410

2A Step-Down

Switch-Mode Regulator

PRELIMINARY

A typical value for R2 can be as high as 100k,

but a typical value is 10kΩ. Using that value,

R1 is determined by:

R1 ~= 8.18 * (VOUT – 1.222) (kΩ).

For example, for a 3.3V output voltage, R2 is

10kΩ, and R1 is 17kΩ.

Input Capacitor

The input current to the step-down converter is

discontinuous, and so a capacitor is required

to supply the AC current to the step-down

converter while maintaining the DC input

voltage.

A low-ESR capacitor is required to keep the

noise at the IC to a minimum. Ceramic

capacitors are preferred, but tantalum or low-

ESR electrolytic capacitors may also suffice.

The input capacitor value should be greater

than 10µF. The capacitor can be electrolytic,

tantalum or ceramic. However since it absorbs

the input switching current it requires an

adequate ripple current rating. Its RMS

current rating should be greater than

approximately 1/2 of the DC load current.

For insuring stable operation CIN should be

placed as close to the IC as possible.

Alternately a smaller high quality ceramic

0.1uF capacitor may be placed closer to the IC

and a larger capacitor placed further away. If

using this technique, it is recommended that

the larger capacitor be a tantalum or

electrolytic type. All ceramic capacitors should

be places close to the MP1410.

Output Capacitor

The output capacitor is required to maintain

the DC output voltage. Low ESR capacitors

are preferred to keep the output voltage ripple

low.

MP1410 Rev 1.0_ 05/29/02

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