EC3293B|3A, 18V, 500KHz, Syn. Step Down DC/DC Conv


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3A, 18V, 500KHz,

Synchronous Step Down DC/DC Converter

 

 

EC3293B

 

General Description

The EC3293B ​​ is a high-frequency, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs. It offers a very compact solution to achieve a 3A continuous output current over a wide input supply range, with excellent load and line regulation. The EC3293B 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 EC3293B requires a minimal number of readily available, standard external components and is available in a space-saving TSOT23-6L package.

 

Features

​​ 4.5V to 18V input voltage

​​ Output adjustable from 0.6V to 15V

​​ Output current up to 3A

​​ Integrated 85mΩ/45mΩ 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

 

 

 

 

 

 

 

 

 

 

Pin 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.

 

Application Information

Note: R5 and C7 are optional.

 

Ordering Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EC3293B

3A, 18V, 500KHz,

Synchronous Step Down DC/DC Converter

 

 

 

Marking Information

Part Number

Package

Marking

Marking Information

EC3293BNT3R

TSOT23-6L

39LXX

Llast one number of lot no.

XXDate Code

        week 1st~ week 26th use YW

week 27th ~ week 52th use WY

Please refer to the table below

 

 

Functional Block Diagram

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absolute Maximum Ratings

 

Supply Voltage VIN ……………………–0.3V to +20V

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

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

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

Junction Temperature ………………………+150°C

Lead Temperature ………………………… +260°C

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

Power [email protected]°C ………………..1.2W

 

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 ……...…………...…….…4.5V 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

 

4.5

 

18

V

Output Voltage

VOUT

 

0.6

 

15

V

Shutdown Supply Current

 

VEN = 0V

 

3

6

µA

Supply Current

 

VEN = 2.0V,VFB =0.66V

 

0.7

 

mA

Feedback Voltage

VFB

4.5V  VIN  18V

0.558

0.6

0.612

V

Feedback Over-voltage Threshold

 

 

 

0.72

 

V

Error Amplifier Voltage Gain *

AEA

 

 

1000

 

V/V

High-Side Switch-On Resistance *

RDS(ON)1

 

 

85

 

Low-side Switch-On Resistance *

RDS(ON)2

 

 

45

 

High-Side Switch Leakage Current

 

VEN = 0V, VSW = 0V,

TA = +125°C

 

 

10

µA

Upper Switch Current Limit

 

Minimum Duty Cycle

3.7

4.3

 

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

200

250

300

KHz

Maximum Duty Cycle

DMAX

VFB = 0.5V

 

90

 

%

Minimum On Time *

 

 

 

90

 

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

 

 

 

 

200

 

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 = 22μF x 2, TA = +25°C, unless otherwise noted.

 

Start UP & Inrush Current (Load 1A)Shut Down (ILoad 1A)

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Ripple (ILoad=2A)Output Ripple (ILoad=1A)

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Ripple (ILoad=0A)Dynamic Load (Iload=0.2A_1.2A)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Short Circuit Protection  ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Efficiency  

 

 

 

 

 

 

 

 

 

 

 

 

       ​​ ​​ ​​ ​​ ​​ ​​​​ 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Application Information

Overview

The EC3293B is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.5V to 18V down to an output voltage as low as 0.6V, and supplies up to 3A of load current.

The EC3293B 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 trans-conductance 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 EC3293B FB pin exceeds 20% 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 0.1μF or 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 4.5V ​​ 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 power to the output. Connect the output

LC  ​​​​ filter  ​​​​ from  ​​​​ SW  ​​​​ to  ​​​​ the  ​​​​ output  ​​​​ load.  ​​​​ Note  ​​​​ that  ​​​​ a capacitor ​​ 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 output voltage. The feedback resistor R1 also sets the feedback loop bandwidth through the internal compensation capacitor.

(see the typical application circuit). Choose the R1 around ​​ 10KΩ,and R2 by ​​ R2=R1/(Vout/0.6V-1)

Use a network for when Vout is low.

 

 

 

 

 

 

 

 

Figure 1:Network

 

 

 

 

 

 

 

 

 

 

Table 1 lists the recommended resistors value for common output voltages.

VOUT (V)

R1 (KΩ)

R2 (KΩ)

LOUT

(μH)

COUT (μF)

1.05

85.3

113.7

2.2

44

1.2

81.5

81.5

2.2

44

1.8

66.5

33.3

3.3

44

2.5

49.0

15.5

4.7

44

3.3

29.0

6.4

4.7

44

5

23.7

3.2

6.8

44

 

Table 1: Resistor selection for common output voltages.

 

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 EC3293B 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%

 

 

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

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

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.

 

 

 

 

 

 

 

 

 

 

 

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

 

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 EC3293B

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

23.7K

3.2K

22μF×2

Vout = 3.3V

4.7μH

29.0K

6.4K

22μF×2

Vout = 2.5V

4.7μH

49.0K

15.5K

22μF×2

Vout = 1.8V

3.3μH

66.5K

33.3K

22μF×2

Vout = 1.2V

2.2μH

81.5K

81.5K

22μF×2

Vout = 1.05V

2.2μH

85.3K

113.7K

22μF×2

Table 4: BOM selection table II.

 

 

 

 

 

 

 

Package Information

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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