MP3213DH-LF-Z Datasheet MP3213DH-LF-P, MP3213DQ-LF-Z, MP3213DH-LF-Z | P7-P9

MP3213 – 700KHZ/1.3MHZ BOOST CONVERTER WITH A 3.5A SWITCH

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APPLICATION INFORMATION

Components referenced below apply to

Typical Application Circuit on page 1.

Selecting the Soft-Start Capacitor

The MP3213 includes a soft-start timer that

limits the voltage at COMP during startup to

prevent excessive current at the input. This

prevents fault tripping of the input voltage at

startup due to input current overshoot. When

power is applied to the MP3213, and enable is

asserted, a 6A internal current source charges

the external capacitor at SS. As the SS

capacitor is charged, the voltage at SS rises.

The MP3213 internally clamps the voltage at

COMP to 700mV above the voltage at SS. The

soft-start ends when the voltage at SS reaches

0.45V. This limits the inductor current at startup,

forcing the input current to rise slowly to the

current required to regulate the output voltage.

The soft-start period is determined by the

equation:

SSSS

C 57t ×=

Where C

(in nF) is the soft-start capacitor

from SS to GND, and t

(in µs) is the soft-start

period.

Determine the capacitor required for a given

soft-start period by the equation:

SSSS

t 0133.0C ×=

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. Use 10k for the low-side

resistor R2 of the voltage divider. Determine the

high-side resistor R1 by the equation:

FBOUT

)VV(2R

−

where V

OUT

is the output voltage.

For R2 = 10k and V

= 1.25V, then

R1 (k) = 8k (V

OUT

– 1.25V).

Selecting the Input Capacitor

An input capacitor (C1) is required to supply the

AC ripple current to the inductor, while limiting

noise at the input source. 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.

Use an input capacitor value greater than 4.7F.

The capacitor can be electrolytic, tantalum or

ceramic. However since it absorbs the input

switching current it requires an adequate ripple

current rating. Use a capacitor with RMS

current rating greater than the inductor ripple

current (see Selecting The Inductor to

determine the inductor ripple current).

To ensure stable operation, place the input

capacitor as close to the IC as possible.

Alternately a smaller high quality ceramic 0.1F

capacitor may be placed closer to the IC with

the larger capacitor placed further away. If

using this technique, the larger capacitor can be

a tantalum or electrolytic type. All ceramic

capacitors should be placed close to the

MP3213.

Selecting the Output Capacitor

The output capacitor is required to maintain the

DC output voltage. Low ESR capacitors are

preferred to keep the output voltage ripple to a

minimum. The characteristic of the output

capacitor also affects the stability of the

regulation control system. Ceramic, tantalum, or

low ESR electrolytic capacitors are

recommended. In the case of ceramic

capacitors, the impedance of the capacitor at

the switching frequency is dominated by the

capacitance, and so the output voltage ripple is

mostly independent of the ESR. The output

voltage ripple is estimated to be:

LOAD

OUT

RIPPLE

f2C

- 1

⎟

⎠

⎞

⎜

⎝

⎛

≈

Where V

RIPPLE

is the output ripple voltage, V

and V

OUT

are the DC input and output voltages

respectively, I

LOAD

is the load current, f

is the

switching frequency, and C2 is the capacitance

of the output capacitor.

MP3213 – 700KHZ/1.3MHZ BOOST CONVERTER WITH A 3.5A SWITCH

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In the case of tantalum or low-ESR electrolytic

capacitors, the ESR dominates the impedance

at the switching frequency, and so the output

ripple is calculated as:

OUTESRLOAD

LOAD

OUT

RIPPLE

VRI

f2C

××

×−

≈

Where R

ESR

is the equivalent series resistance

of the output capacitors.

Choose an output capacitor to satisfy the output

ripple and load transient requirements of the

design. A 4.7F-22F ceramic capacitor is

suitable for most applications.

Selecting the Inductor

The inductor is required to force the higher

output voltage while being driven by the input

voltage. A larger value inductor results in less

ripple current that results in lower peak inductor

current, reducing stress on the internal

N-Channel.switch. However, the larger value

inductor has a larger physical size, higher

series resistance, and/or lower saturation

current.

A 4.7µH inductor is recommended for most

1.3MHz applications and a 10µH inductor is

recommended for most 700KHz applications.

However, a more exact inductance value can

be calculated. A good rule of thumb is to allow

the peak-to-peak ripple current to be

approximately 30-50% of the maximum input

current. Make sure that the peak inductor

current is below 75% of the current limit at the

operating duty cycle to prevent loss of

regulation due to the current limit. Also make

sure that the inductor does not saturate under

the worst-case load transient and startup

conditions. Calculate the required inductance

value by the equation:

I f V

) V-(V V

OUT

INOUTIN

Δ×

η×

)MAX(

LOADOUT

)MAX(IN

(

)

)MAX(IN

I%50%30I −

Where I

LOAD(MAX)

is the maximum load current, I

is the peak-to-peak inductor ripple current, and 

is efficiency.

Selecting the Diode

The output rectifier diode supplies current to the

inductor when the internal MOSFET is off. To

reduce losses due to diode forward voltage and

recovery time, use a Schottky diode with the

MP3213. The diode should be rated for a

reverse voltage equal to or greater than the

output voltage used. The average current rating

must be greater than the maximum load current

expected, and the peak current rating must be

greater than the peak inductor current.

Compensation

The output of the transconductance error

amplifier (COMP) is used to compensate the

regulation control system. The system uses two

poles and one zero to stabilize the control loop.

The poles are f

set by the output capacitor C2

and load resistance and f

set by the

compensation capacitor C3. The zero f

is set

by the compensation capacitor C3 and the

compensation resistor R3. These are

determined by the equations:

LOAD

R C2

××π

VEA

A C3 2

××π×

R3 C3 2

××π×

Where R

LOAD

is the load resistance, G

is the

error amplifier transconductance, and A

VEA

the error amplifier voltage gain.

The DC loop gain is:

LOAD

OUT

FBIN

VEA

VDC

V R V A5.1

××××

Where V

is the feedback regulation threshold.

MP3213 – 700KHZ/1.3MHZ BOOST CONVERTER WITH A 3.5A SWITCH

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There is also a right-half plan zero (f

RHPZ

) that

exists in continuous conduction mode (inductor

current does not drop to zero on each cycle)

step-up converters. The frequency of the right

half plane zero is:

OUT

LOAD

RHPZ

VL2

R V

××π×

Table 1 lists generally recommended

compensation components for different input

voltage, output voltage and capacitance of most

frequently used output ceramic capacitors.

Ceramic capacitors have extremely low ESR,

therefore the second compensation capacitor

(from COMP to GND) is not required.

Table 1—Component Selection

(V)

OUT

(V)

(µF)

(kΩ)

(nF)

3.3 8 4.7 10 2.2

3.3 8 10 10 2.2

3.3 8 22 10 2.2

3.3 12 4.7 15 1

3.3 12 10 15 1

3.3 12 22 15 2.2

3.3 18 4.7 20 1

3.3 18 10 20 1

3.3 18 22 30 2.2

5 8 4.7 10 4.7

5 8 10 10 4.7

5 8 22 15 1

5 12 4.7 15 2.2

5 12 10 15 2.2

5 12 22 20 1

5 18 4.7 20 1

5 18 10 20 1

5 18 22 30 1

12 15 4.7 10 2.2

12 15 10 10 2.2

12 15 22 15 1

12 18 4.7 5.1 2.2

12 18 10 5.1 2.2

12 18 22 15 1

For faster control loop and better transient

response, set the capacitor C3 to the

recommended value in Table 1. Then slowly

increase the resistor R3 and check the load

step response on a bench to make sure the

ringing and overshoot on the output voltage at

the edge of the load steps is minimal. Finally,

the compensation needs to be checked by

calculating the DC loop gain and the crossover

frequency. The crossover frequency where the

loop gain drops to 0dB or a gain of 1 can be

obtained visually by placing a –20dB/decade

slope at each pole, and a +20dB/decade slope

at each zero. The crossover frequency should

be at least one decade below the frequency of

the right-half-plane zero at maximum output

load current to obtain high enough phase

margin for stability.

Layout Consideration

High frequency switching regulators require very

careful layout for stable operation and low noise.

All components must be placed as close to the IC

as possible. Keep the path between the SW pin,

output diode, output capacitor and GND pin

extremely short for minimal noise and ringing. The

input capacitor must be placed close to the IN pin

for best decoupling. All feedback components

must be kept close to the FB pin to prevent noise

injection on the FB pin trace. The ground return of

the input and output capacitors should be tied

close to the GND pin. See the MP3213 demo

board layout for reference.

P1-P3 P4-P6 P7-P9 P10-P12

MP3213DH-LF-Z

Mfr. #:

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Description:

Switching Voltage Regulators 700KHz/1.3MHz Boost Converter

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MP3213DH-LF-Z

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