MPQ2560DQ-LF-Z Datasheet MPQ2560DQ-LF-P, MPQ2560DN-LF-Z, MPQ2560DQ-LF-Z | P13-P15

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The input capacitor (C1) can be electrolytic,

tantalum or ceramic. When using electrolytic or

tantalum capacitors, a small, high quality

ceramic capacitor, i.e. 0.1ȝF, should be placed

as close to the IC as possible. When using

ceramic capacitors, make sure that they have

enough capacitance to provide sufficient charge

to prevent excessive voltage ripple at input. The

input voltage ripple caused by capacitance can

be estimated by:

uu

OUT

LOAD

1Cf

Output Capacitor

The output capacitor (C2) is required to

maintain the DC output voltage. Ceramic,

tantalum, or low ESR electrolytic capacitors are

recommended. Low ESR capacitors are

preferred to keep the output voltage ripple low.

The output voltage ripple can be estimated by:

u

u

2Cf8

ESR

OUT

Where L is the inductor value and R

ESR is the

equivalent series resistance (ESR) value of the

output capacitor.

In the case of ceramic capacitors, the

impedance at the switching frequency is

dominated by the capacitance. The output

voltage ripple is mainly caused by the

capacitance. For simplification, the output

voltage ripple can be estimated by:

u

uuu

OUT

2CLf8

ǻV

In the case of tantalum or electrolytic capacitors,

the ESR dominates the impedance at the

switching frequency. For simplification, the

output ripple can be approximated to:

ESR

OUT

ǻV u

u

The characteristics of the output capacitor also

affect the stability of the regulation system. The

MPQ2560 can be optimized for a wide range of

capacitance and ESR values.

Compensation Components

MPQ2560 employs current mode control for

easy compensation and fast transient response.

The system stability and transient response are

controlled through the COMP pin. COMP pin is

the output of the internal error amplifier. A

series capacitor-resistor combination sets a

pole-zero combination to control the

characteristics of the control system. The DC

gain of the voltage feedback loop is given by:

OUT

VEACSLOADVDC

AGRA uuu

Where A

VEA is the error amplifier voltage gain,

200V/V; G

CS is the current sense

transconductance, 8A/V; R

LOAD is the load

resistor value.

The system has two poles of importance. One

is due to the compensation capacitor (C3), the

output resistor of error amplifier. The other is

due to the output capacitor and the load resistor.

These poles are located at:

VEA

A3C2

uuS

LOAD

R2C2

uuS

Where, G

EA is the error amplifier

transconductance, 60ȝA/V.

The system has one zero of importance, due to

the compensation capacitor (C3) and the

compensation resistor (R3). This zero is located

at:

3R3C2

uuS

The system may have another zero of

importance, if the output capacitor has a large

capacitance and/or a high ESR value. The zero,

due to the ESR and capacitance of the output

capacitor, is located at:

ESR

R2C2

uuS

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In this case (as shown in Figure 2), a third pole

set by the compensation capacitor (C6) and the

compensation resistor (R3) is used to

compensate the effect of the ESR zero on the

loop gain. This pole is located at:

3R6C2

uuS

The goal of compensation design is to shape

the converter transfer function to get a desired

loop gain. The system crossover frequency

where the feedback loop has the unity gain is

important. Lower crossover frequencies result

in slower line and load transient responses,

while higher crossover frequencies could cause

system unstable. A good rule of thumb is to set

the crossover frequency to approximately one-

tenth of the switching frequency. The Table 3

lists the typical values of compensation

components for some standard output voltages

with various output capacitors and inductors.

The values of the compensation components

have been optimized for fast transient

responses and good stability at given conditions.

Table 3—Compensation Values for Typical

Output Voltage/Capacitor Combinations

OUT

(V)

L1 (μH)

(μF)

(k)

(pF)

1.8 4.7 47 105 100 None

2.5 4.7 - 6.8 33 54.9 330 None

3.3 6.8 -10 22 68.1 220 None

5 15 - 22 22 100 150 None

12 22 33 147 150 None

To optimize the compensation components for

conditions not listed in Table 3, the following

procedure can be used.

1. Choose the compensation resistor (R3) to set

the desired crossover frequency. Determine the

R3 value by the following equation:

OUT

CSEA

f2C2

3R u

uuS

Where f

C is the desired crossover frequency.

2. Choose the compensation capacitor (C3) to

achieve the desired phase margin. For

applications with typical inductor values, setting

the compensation zero, f

Z1, below one forth of

the crossover frequency provides sufficient

phase margin. Determine the C3 value by the

following equation:

f3R2

uuS

3. Determine if the second compensation

capacitor (C6) is required. It is required if the

ESR zero of the output capacitor is located at

less than half of the switching frequency, or the

following relationship is valid:

R2C2

ESR



uuS

If this is the case, then add the second

compensation capacitor (C6) to set the pole f

at the location of the ESR zero. Determine the

C6 value by the equation:

R2C

ESR

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High Frequency Operation

The switching frequency of MPQ2560 can be

programmed up to 4MHz by an external resistor.

Please pay attention to the following if the

switching frequency is above 2MHz.

The minimum on time of MPQ2560 is about

100ns (typ). Pulse skipping operation can be

seen more easily at higher switching frequency

due to the minimum on time. Recommended

operating voltage is 12V or below, and 24V or

below at 2MHz. Refer to Figure 2 below for

detailed information.

Recommended VIN (max)

vs Switching Frequency

1500 2000 2500 3000 3500 4000

OUT

=3.3V

(KHz)

IN (MAX)

(V)

OUT

=2.5V

Figure 2—Recommend Max V

vs. f

Since the internal bootstrap circuitry has higher

impedance, which may not be adequate to

charge the bootstrap capacitor during each (1-

D)×Ts charging period, an external bootstrap

charging diode is strongly recommended if the

switching frequency is above 2MHz (see

External Bootstrap Diode section for detailed

implementation information).

With higher switching frequencies, the inductive

reactance (X

) of capacitor comes to dominate,

so that the ESL of input/output capacitor

determines the input/output ripple voltage at

higher switching frequency. As a result of that,

high frequency ceramic capacitor is strongly

recommended as input decoupling capacitor

and output filtering capacitor for such high

frequency operation.

Layout becomes more important when the

device switches at higher frequency. It is

essential to place the input decoupling

capacitor, catch diode and the MPQ2560 (Vin

pin, SW pin and PGND) as close as possible,

with traces that are very short and fairly wide.

This can help to greatly reduce the voltage

spike on SW node, and lower the EMI noise

level as well.

Try to run the feedback trace as far from the

inductor and noisy power traces as possible. It

is often a good idea to run the feedback trace

on the side of the PCB opposite of the inductor

with a ground plane separating the two. The

compensation components should be placed

closed to the MPQ2560. Do not place the

compensation components close to or under

high dv/dt SW node, or inside the high di/dt

power loop. If you have to do so, the proper

ground plane must be in place to isolate those.

Switching loss is expected to be increased at

high switching frequency. To help to improve

the thermal conduction, a grid of thermal vias

can be created right under the exposed pad. It

is recommended that they be small (15mil

barrel diameter) so that the hole is essentially

filled up during the plating process, thus aiding

conduction to the other side. Too large a hole

can cause ‘solder wicking’ problems during the

reflow soldering process. The pitch (distance

between the centers) of several such thermal

vias in an area is typically 40mil. Please refer to

the layout example on EV2560 datasheet.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P20

MPQ2560DQ-LF-Z

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Description:

Switching Voltage Regulators 2.5A, 4MHz, 42V Buck Converter

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MPQ2560DQ-LF-Z

MPQ2560DQ-LF-Z

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