AME5244 PDF 2.4A车充IC

AME

AME5244

40V CC/CV Buck Converter

n General Description

The AME5244 is a specific 40V HV buck converter that operates in either CV/CC mode supports an output volt-age range of 0.8V to 12V and support constant output current at 200KHz switching frequency.

Protection features include under voltage protection,over voltage protection, current limit, thermal shutdown,and short circuit protection. The device is available in SOP-8/PP package with exposed pad for low thermal resistance.

n Features

n Application

l Car Charger l Wall Adapter

l 40V Maximum Rating for Input Power l 200KHz Switching Frequency l CC/CV Mode Function l Internal Soft Start

l UVP , Input/Output OVP , OTP , SCP l Available in SOP-8/PP Package l RoHS Compliant and Halogen Free

n Functional Block Diagram

n Typical Application

AME5244-AZAADJ-24

C3

R4 https://www.wendangku.net/doc/4114963960.html,

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AME5244

40V CC/CV Buck Converter

n Pin Configuration

SOP-8/PP Top View

AME5244-AZAADJ

1.IN

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3.NC

4.NC

5.FB

6.GND

7.SW

8.BS

* Die Attach:

Conductive Epoxy

n Pin Description

1324

5

6

7

8

AME5244

40V CC/CV Buck Converter

n Ordering Information

Number of Pins Package Type Pin Configuration

AME5244 - x x x xxx - xx

Output Voltage S pecial Feature Special Feature

A

1. IN

Z:SOP/PP

A:8ADJ:Adjustable

10(SOP-8/PP)

2. COMP 24

3. NC

4. NC

5. FB

6. GND

7. SW

8. BS

Pin Configuration

Package

Type Number of Pins Output Voltage

AME524440V CC/CV Buck Converter n Absolute Maximum Ratings

n Recommended Operating Conditions

JC

AME524440V CC/CV Buck Converter n Electrical Specifications

Typical values V

IN =12V with typical T

A

=25o C, unless otherwise specified.

AME5244

40V CC/CV Buck Converter

Under Voltage Lockout (UVLO)

The AME5244 incorporates an under voltage lockout

circuit to keep the device disabled when V IN (the input voltage) is below the UVLO rising threshold voltage. Once the UVLO rising threshold voltage is reached,the device start-up begins. The device operates until V IN falls below the UVLO falling threshold voltage. The typical hyster-esis in the UVLO comparator is 1V .Over Voltage Protection

The AME5244 has input and output over-voltage pro-tections. The thresholds of input and output OVP circuit include are typicapl 35V and minimum 106% x V OUT , re-spectively. Once the input voltage or output voltage is higher than the threshold, the high-side MOSFET is turned off. When the input voltage or output voltage drops lower than the threshold, the high-side MOSFET will be en-abled again.

Over Current Protection

The AME5244 cycle-by-cycle limits the peak inductor current to protect embedded switch from dameage. High-side switch current limiting is implemented by monitor-ing the current through the high side MOSFET .Thermal Shutdown

The AME5244 protects itself from overheating with an internal thermal shutdown circuit. If the junction tempera-ture exceeds the thermal shutdown trip point, the high-side MOSFET is turned off. The part is restarted when the junction temperature drops 20o C below the thermal shutdown trip point

Setting the Output Voltage

The output voltage is using a resistive voltage divider connected from the output voltage to FB. It divides the output voltage down to the feedback voltage by the ratio:

2

12

R R R V V out

FB +×=n Detailed Description

the output voltage is:

Inductor Selection

The inductor is required to supply contant current to the load while being driven by the switched input voltage.A larger value inductor will have a larger physical size and higher series resistance. It will result in less ripple current that will in turn result in lower output ripple volt-age. Make sure that the peak inductor current is below the maximum switch current limit. Determine inductance is to allow the peak-to-peak ripple current to be approxi-mately 30% of the maximum load current. The induc-tance value can be calculated by:

?×?×=

in out L s out V V I f V L 1Where f S is the switching frequency, V IN is the input

voltage, V OUT is the output voltage, and ?ΙL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak cur-rent, calculated by:

Where I LOAD is the load current. The choice of which

style inductor to use mainly depends on the price vs.size requirements and any EMI constraints.Input Capacitor

The input current to the step-down converter is discon-tinuous, therefore a capacitor is required to supply the AC current while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR elec-trolytic capacitors will also be suggested. Choose X5R or X7R dielectrics when using ceramic capacitors.

2

218.0R R R V out

+×=

?×××+

=in out s out

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AME5244

40V CC/CV Buck Converter

Since the input capacitor (C1) absorbs the input switch-ing current, it requires an adequate ripple current tating.The RMS current in the input capacitor can be esimated by:

At V IN =2V OUT , where I C1 = I LOAD /2 is the worst-case con-dition occurs. For simplification, use an input capacitor

with a RMS current rating greater than half of the maxi-mum load current. When using ceramic capacitors, make sure that they have enough capacitance to provide suffi-cient charge to prevent excessive voltage ripple at input.When using electrolytic or tantalum capacitors, a high quality, small ceramic capacitor, i.e. 0.1μF, should be placed as close to the IC as possible. The input voltage ripple for low ESR capacitors can be estimated by:

Where C1 is the input capacitance value.Output Capacitor

The output capacitor (C2) is required to maintain the

DC output voltage. Ceramic, tantalum, or low ESR electrolutic capacitors are recommended. Low ESR ca-pacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by:

Where R ESR is the equivalent series resistance (ESR)value of the output capacitor and C2 is the output capaci-tance value.

When using ceramic capacitors, the impandance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. For simplification, the output voltage ripple can be estimated by:

?×××=

in out in out

s LOAD C V V V V f C I I 111 When using tantalum or electrolytic capacitors, the

ESR dominates the impedance at the switching frequency.For simplification, the output ripple can be approximated to:

The characteristics of the output capacitor also affect the stability of the regulation system.Rectifier Diode

Use a Schottky diode as the rectifier to conduct cur-rent when the High-Side MOSFET is turned off. The Schottky diode must have current rating higher than the maximum output current and a reverse voltage rating higher than the maximum input https://www.wendangku.net/doc/4114963960.html,pensation Components

AME5244 has current mode control for easy compen-sation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP is the output of the internal transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to govern the characteris-tics of the control system. The DC gain of the voltage feedback loop is given by:

Where V FB is the feedback voltage (0.8V), A VEA is the error amplifier voltage gain, G CS is the current sense transconducductance and R LOAD is the load resistor value.The system has two poles of importance. One is due to the output capacitor and the load resistor, and the other is due to the compansation capacitor (C4) and the output resistor of the error amplifier. These poles are located at:

?××××=

?in out s out

out V V C L f V V 1282

××+× ?××=?281

1C f R V V L f V V s ESR in out s out out

ESR

in out s out out R V V L f V V ×

?××=

?1out

FB

EA CS LOAD VDC V V A G R A ×

××=

?××

=in out in out LOAD C V V V V I I 11VEA EA

P A C G f ×××=421πLOAD

P R C f ×××=

221

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AME5244

40V CC/CV Buck Converter

Where G EA is the error amplifier transconducductance.The system has one zero of importance, due to the com-pensation capacitor (C4) and the compensation resistor (R3). This zero is located at:

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:

In this case, a third pole set by the second compensa-tion capacitor (C5) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at:

The goal of compensation design is to shape the con-verter 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 insta-bility. A good standard is to set the crossover frequency below one-tenth of the switching frequency. To optimize the compensation components, the following procedure can be used.

1. Choose the compensation resistor (R3) to set the desired crossover frequency.

Determine R3 by the following equation:

Where f C is the desired crossover frequency which is

typically below one tenth of the switching frequency.

3

421

1R C f Z ×××=

πESR

ESR R C f ×××=

221

π3

521

3R C f P ×××=

π 2. Choose the compensation capacitor (C4) to achieve

the desired phase margin. For applications with typical inductor values, setting the compensation zero (f Z1) be-low one-forth of the crossover frequency provides suffi-cient phase margin.

Determine C4 by the floolwing equation:

Where R3 is the compensation resistor.

3. Determine if the second compensation capacitor (C5)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:

If this is the case, then add the second compensation capacitor (C5) to set the pole f P3 at the location of the ESR zero. Determine C5 by the equation:

FB

out

CS EA c FB out CS EA c V V G G f C V V G G f C R ×××××<

××××=

1.022223c

f R C ×××>

324

4π2

221s

ESR f

R C <×××π3

25R R C C ESR

×=

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AME5244

40V CC/CV Buck Converter

PC Board Layout Guidance

When laying out the printed circuit board, the following checklist should be uesd to ensure proper operation of the IC.1) Arrange the power components to reduce the AC loop size consisting of C IN , IN pin, SW pin and the sckottky diode.2) Place input decoupling ceramic capacitor C IN as close to IN pin as possible. C IN is connected power GND with vias or

short and wide path.

3) Return FB and COMP to signal GND pin, and connect the singal GND to power GND at a single point for the best noise immunity. Connect exposed pad to power ground copper area with copper and vias.4) Use copper plane for power GND for best heat disspation and noise immunity.5) Please feedback resistor close to FB pin.

Top Layer

Bottom Layer

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AME5244

40V CC/CV Buck Converter

n Radiated EMI Data (Vertical)

n

Radiated EMI Data (Horizontal)

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AME5244

40V CC/CV Buck Converter

n Characterization Curve

Efficiency vs. Output Current

I-V Curve

Power ON from V IN

Full Load Ripple Load Transient Response

60657075808590

951000.0

0.5

1.0

1.5

2.0

2.5

Output Current (A)

E f f i c i e n c y (%

)

V IN

(10V/div)V OUT (2V/div)

V SW

(5V/div)

Time (10.0ms/div)

Power Off from V IN

1.0

2.0

3.0

4.0

5.0

6.0

00.5 1.0 1.5 2.0 2.5 3.0

Load Current I OUT (A)

O u t p u t V o l t a g e V O U T (V

)

Time (2.0μs/div )

V OUT

(20mV/div)

V SW

(5V/div)

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AME5244

40V CC/CV Buck Converter

n Characterization Curve (Contd.)

0A Short

2A Short

Input Voltage vs. Constant Current

Load Transient Response

Load Transient Response

8

9

10

11

12

13

14

15

Input Voltage (V)

C o n s t a n t C u r r e n t (A

)

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AME5244

40V CC/CV Buck Converter

n Characterization Curve

Frequency vs. Temperature

V FB VS Temperature

S tanby Current vs. Temperature

0.78

0.79

0.80

0.81

0.82

-40

-200

20406080100Temperature (°C)

V F B (V )

0.00

1.00

2.00

3.00

4.00

5.00-40-200

20406080100

Temperature (°C)

S t a n d b y C u r r e n t (m A )

100.0

150.0

200.0

250.0

300.0

-40

-20020406080100

Temperature (°C)

F r e q u e n c y (K H z )

Input OVP vs. Temperature

2.00

2.20

2.402.602.80

3.003.203.403.60

3.80

-40

-20020406080100

Temperature (°C)

C C C u r r e n t (A )

CC Current vs. Temperature

30.0

31.032.033.034.035.036.037.038.0

39.040.0I n p u t O V P (V )

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AME5244

40V CC/CV Buck Converter

n Tape and Reel Dimension

SOP-8/PP

FRONT VIEW

SIDE VIEW

TOP VIEW

n Package Dimension

SOP-8/PP

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