EC3292B|18V/2A Synchronous Step-Down DC/DC Convert


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EC3292B

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 2A, 18V, 500KHz, Synchronous

Step-Down DC/DC Converter

 

 

 

 

General Description

 

 

The EC3292B is a high-frequency, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs. It offers a very compact solution to achieve a 2A continuous output current over a wide input supply range, with excellent load and line regulation. The EC3292B has synchronous-mode operation for higher efficiency over the output current-load range.

Current-mode ​​ operation ​​ provides ​​ fast ​​ transient response and eases loop stabilization.

Protection features include over-current protection and thermal shutdown.

The EC3292B requires a minimal number of readily available, standard external components and is available in space-saving TSOT23-6L package.

 

 

Features

 

 

  4.7V to 18V input voltage

  Output adjustable from 0.6V to 15V

  Output current up to 2A

  Integrated 140mΩ/90 power MOSFET switches

  Shutdown current 3μA typical

  Efficiency up to 95%

  Fixed frequency 500KHz

  Internal soft start

  Over current protection and Hiccup

  Over temperature protection

  RoHS Compliant and 100% Lead (Pb) Free

 

 

Applications

 

  Distributed power systems

  Networking systems

  FPGA, DSP, ASIC power supplies

  Notebook computers

  Green electronics or appliance

 

 

Pin Assignments  ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Pins Description

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 

TSOT23-6L

Symbol

Description

1

BOOT

High-side gate drive boost input.

2

GND

Ground.

3

FB

Feedback input.

4

EN

Enable input.

5

IN

Power input.

6

SW

Power switching output.

 

 

6C29N-Rev.F001

Page 1​​ of 12

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 2A, 18V, 500KHz, Synchronous

Step-Down DC/DC Converter

 

EC3292B

 

 

Application Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: R5 and C7 are optional.

Details please see the DVT report.

 

 

Ordering Information

 

RTape & reel

T3TSOT23-6

EC3292BN XX X

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A: Product ID+B: Lot Number+ C:Date Code (XXXXX)

 

Product ID: 29

Date Code:week 1st~ week 26th use YW

week 27th ~ week 52th use WY

Please refer to the table below

 

 

 

 

 

 

 

 

 

Year

Marking(Y)

2010

0

2011

1

2012

2

2013

3

2014

4

2015

5

2016

6

2017

7

2018

8

2019

9

Week

Marking(W)

1; 27

A

2; 28

B

3; 29

C

4; 30

D

5; 31

E

6; 32

F

7; 33

G

8; 34

H

9; 35

I

10; 36

J

11; 37

K

12; 38

L

13; 39

M

14; 40

N

15; 41

O

16; 42

P

17; 43

Q

18; 44

R

19; 45

S

20; 46

T

21; 47

U

22; 48

V

23; 49

W

24; 50

X

25; 51

Y

26; 52

Z

 

 

 

 

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 2A, 18V, 500KHz, Synchronous

Step-Down DC/DC Converter

 

EC3292B

​​ 

 

Functional Block Diagram

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute Maximum Ratings

 

Supply Voltage VIN ……………………–0.3V to +19V

Switch Node VSW ……………… –0.3V to VIN+0.3V

Boost VBOOT ………………… VSW–0.3V to VSW+6V

All Other Pins ………………………… –0.3V to +6V

Power Dissipation @25…………………… 1.2W

Junction Temperature ………………………+150°C

Lead Temperature ………………………… +260°C

Storage Temperature Range ……–65°C to +150°C

ESD, HBM ……………………………………… 2KV

ESD, MM ………………………………………. 200V

 

CAUTION:   Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device.

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ This is a stress only rating and operation of the device at these or any other conditions above those Indicated

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​  in the operational sections of this specification is not implied.

 

 

 

 

 

 

 

 

 

 

 

 

Recommended Operating Conditions

Supply Voltage VIN ……...…………...…….…4.7V to 18V

Output Voltage VOUT ……...…………... ​​ 0.6V to VIN–3V

Operating Temperature Range ……...…–40°C to +125°C

 

Package Thermal Characteristics

 

TSOT23-6L:

Thermal  Resistance,  θJA  ………………………100°C/W

Thermal Resistance, θJC …………………………   ​​​​ 55°C/W

 

Electrical Characteristics(TA = +25°C, VIN = +12V, unless otherwise noted.)

 

PARAMETER

Symbol

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Supply Voltage

VIN

 

4.7

 

18

V

Output Voltage

VOUT

 

0.8

 

15

V

Shutdown Supply Current

 

VEN = 0V

 

3

6

µA

Supply Current

 

VEN = 2.0V,VFB =0.64V

 

0.7

 

mA

Feedback Voltage

VFB

4.7V  VIN  18V

0.588

0.6

0.612

V

Feedback Over-voltage Threshold

 

 

 

0.66

 

V

Error Amplifier Voltage Gain *

AEA

 

 

1000

 

V/V

High-Side Switch-On Resistance *

RDS(ON)1

 

 

140

 

Low-side Switch-On Resistance *

RDS(ON)2

 

 

90

 

High-Side Switch Leakage Current

 

VEN = 0V, VSW = 0V,

TA = +125°C

 

 

10

µA

Upper Switch Current Limit

 

Minimum Duty Cycle

3

3.6

 

A

Lower Switch Current Limit

 

From Drain to Source

 

0

 

A

Oscillation Frequency

 ​​ ​​ ​​​​ FOSC1

 

400

500

600

KHz

Short Circuit Oscillation Frequency

FOSC2

VFB = 0V

100

125

150

KHz

Maximum Duty Cycle

DMAX

VFB = 0.5V

 

90

 

%

Minimum On Time *

 

 

 

120

 

ns

EN Falling Threshold Voltage

 

VEN Falling

 

1.12

 

V

EN Rising Threshold Voltage

 

VEN Rising

 

1.22

 

V

Input Under Voltage Lockout Threshold

 

VIN Rising

 

3.5

 

V

Input Under Voltage Lockout Threshold

Hysteresis

 

 

 

 

240

 

mV

Soft-Start Period

 

​​ 

 

1

 

ms

Thermal Shutdown *

 

 

 

150

 

°C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Guaranteed by design, not tested.

 

 

 

Typical Characteristics

 

 ​​​​ ​​ VIN = 12V, VO = 3.3V, L1 = 4.7μH, C1 = 10μF, C2 = 10μF x 2, TA = +25°C, unless otherwise noted.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Application Information

 

Overview

 

The EC3292B is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.7V to 18V ​​ down to an output voltage as low as 0.8V, and supplies up to 2A of load current.

The ​​ EC3292B ​​ 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 transconductance error amplifier. The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output voltage. Since the high side MOSFET ​​ requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and ​​ BOOT is needed to ​​ drive the high side gate. The boost capacitor is charged from the internal 5V rail when SW is low. When the EC3292B FB  ​​​​ pin exceeds 10% of the nominal regulation voltage of 0.6V, the over voltage comparator is tripped forcing the high-side switch off.

 

 

Pins Description

 

BOOT: High-Side Gate Drive Boost Input. BOOT supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.1μFor greater capacitor from SW to BOOT to power the high side switch.

 

IN: Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 4.7V to 18V ​​ power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC.

 

SW: Power Switching Output. SW is the switching node that supplies is required from SW to BOOT ​​ to power the high-side switch.

 

GND: Ground.

 

FB: ​​ Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback threshold is 0.6V.

 

EN: ​​ Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.

 

 

Setting the Output Voltage

 

The external resistor divider sets the output voltage. The feedback resistor R1 also sets the feedback-loop

bandwidth through the internal compensation capacitor (see the Typical Application circuit). Choose R1 around

10kΩ, and R2 by:

 

R2 = R1 / (VOUT/0.6V – 1)

 

Use a network below for when VOUT is low.

 

 

 

 

 

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Figure 1:feedback network

 

Table 1 lists the recommended ​​ resistors value for common output voltages.(RT=0)

VOUT (V)

R1 (KΩ)

R2 (KΩ)

1.05

95(1%)

126.7(1%)

1.2

90(1%)

90(1%)

1.8

70(1%)

35(1%)

2.5

46.7(1%)

14.7(1%)

3.3

20(1%)

4.4(1%)

5

41.4(1%)

5.6(1%)

 

 

 

 

 

 

 

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Table 1: Resistor selection for common output voltages.

 

Rt is used to set control loop’s bandwidth, which is proportional to the relation by R1, R2, RT:

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 1/[(Rt+20k)*(1+R1/R2)+R1]

 

So Increase RT & Decrease R1&R2 value(keeping R1/R2 ratio), the bandwidth can be kept the same(the relation value need to be the same)

 

Inductor

 

The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A 

larger value inductor will result in less ripple current that will result in lower output ripple voltage. However, the larger value

inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum 

switch current limit. Also, make sure that the peak inductor current is below the maximum switch current limit. The inductance value can be calculated by:

​​ 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ L = [ VOUT / (fS × ΔIL) ] × (1 − VOUT/VIN)

 

Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ΔIL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by:

 

ILP = ILOAD + [ VOUT / (2 × fS × L) ] × (1 − VOUT/VIN)

 

Where ILOAD is the load current.

The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirements.

 

Optional Schottky Diode

 

During the transition between high-side switch and low-side switch, the body diode of the low-side power MOSFET conducts ​​ the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be paralleled between the SW pin and GND pin to improve ​​ overall ​​ efficiency. ​​ Table ​​ 2 ​​ lists ​​ example Schottky diodes and their Manufacturers.

 

Part

Number

Voltage and

Current Rating

Vendor

B130

30V, 1A

Diodes Inc.

SK13

30V, 1A

Diodes Inc.

MBRS130

30V, 1A

International Rectifier

Table 2: Diode selection guide.

 

Input Capacitor

 

The input current to the step-down converter is discontinuous, ​​ therefore a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Choose X5R or X7R dielectrics when using ceramic capacitors.Since the input capacitor (C1) absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by:

 

IC1 = ILOAD × [ (VOUT/VIN) × (1 − VOUT/VIN) ]1/2

 

The worst-case condition occurs at VIN = 2VOUT, where IC1= ILOAD /2. ​​ For simplification, choose the input capacitor whose  ​​​​ RMS current rating greater than half of the maximum load current. The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1μF, 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 for low ESR capacitors can be estimated by:

 

ΔVIN = [ ILOAD/(C1 × fS) ] × (VOUT/VIN) × (1 − VOUT/VIN)

 

Where C1 is the input capacitance value.

 

Output Capacitor

 

The output capacitor 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:

 

ΔVOUT = [ VOUT/(fS × L) ] × (1 − VOUT/VIN) × [ RESR + 1 / (8 × fS × C2) ]

 

Where C2 is the output capacitance value and RESR 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:

 

ΔVOUT = [ VOUT/(8xfS2 xLxC2)] × (1 − VOUT/VIN)

 

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:

 

ΔVOUT = [ VOUT/(fS × L) ] × (1 − VOUT/VIN) × RESR

 

The characteristics of the output capacitor also affect the stability of the regulation system. The EC3292B can be optimized for a wide ​​ range of capacitance and ESR values.

 

External Bootstrap Diode

 

An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BOOT diode are:

 

​​ VOUT = 5V or 3.3V; and

​​ Duty cycle is high: D = VOUT/VIN > 65%

 

In these cases, an external BOOT diode is recommended from the output of the voltage regulator to BOOT pin, as shown in Figure 2.

 

 

EC3292B

 

 

 

 

 

 

​​ 

Figure 2: Add optional external bootstrap diode to enhance efficiency.

 

The recommended external BOOT diode is IN4148, and the BOOT capacitor is 0.1 ~ 1μF.

 

When VIN ≤ 6V, ​​ for the purpose of promote the efficiency, it can add an external Schottky diode between IN and BOOT pins, as shown in Figure 3

 

 

EC3292B

 

 

 

 

 

 

 

 

 

 

Figure 3: Add a Schottky diode to promote efficiency when VIN ≤ 6V.

 

 

L1

R1

R2

C2

Vout = 5.0V

6.8μH

41.4K

5.6K

10μF×2

Vout = 3.3V

4.7μH

20K

4.4K

10μF×2

Vout = 2.5V

3.3μH

46.7K

14.7K

10μF×2

Vout = 1.8V

2.2μH

70K

35K

10μF×2

Vout = 1.2V

2.2μH

90K

90K

10μF×2

Vout = 1.05V

2.2μH

95K

126K

10μF×2

 

 

 

 

 

 

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Table 4: BOM selection table II

 

PCB Layout Guide

 

PCB layout is very important to achieve stable operation. Please follow the guidelines below.

1) Keep the path of switching current short and minimize the loop area formed by Input capacitor,

high-side MOSFET and low-side MOSFET.

2) Bypass ceramic capacitors are suggested to be put close to the VIN Pin.

3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as

 ​​ ​​ ​​​​ close to the chip as possible.

4) Rout SW away from sensitive analog areas such as FB

5) Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance

 ​​ ​​​​ and long-term reliability.

 

BOM of EC3292B

 

Please refer to the Typical Application Circuit.

Item

Reference

Part

1

C1

10μF

2

C5

100nF

3

C7

0.1μF

4

R4

100K

 

 

 

 

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Table 3: BOM selection table I.

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ 

 

L1

R1

R2

C2

Vout = 5.0V

6.8μH

41.4K

5.6K

10μF×2

Vout = 3.3V

4.7μH

20K

4.4K

10μF×2

Vout = 2.5V

3.3μH

46.7K

14.7K

10μF×2

Vout = 1.8V

2.2μH

70K

35K

10μF×2

Vout = 1.2V

2.2μH

90K

90K

10μF×2

Vout = 1.05V

2.2μH

95K

126K

10μF×2

 

 

 

 

 

 

 

Table 4: BOM selection table II.

 

 

 

PACKAGE DIMENSION ​​ TSOT23-6L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Symbol

Dimensions in mm

Dimensions in Inch

Min

Max

Min

Max

A

0.700

0.900

0.028

0.035

A1

0.000

0.100

0.000

0.004

B

1.600

1.700

0.063

0.067

b

0.350

0.500

0.014

0.020

C

2.650

2.950

0.104

0.116

D

2.820

3.020

0.111

0.119

e

0.950 BSC

0.037 BSC

H

0.080

0.200

0.003

0.008

L

0.300

0.600

0.012

0.024

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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