EC3293A|3A, 18V, 500KHz, Syn. DC/DC Converter


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3A, 18V, 500KHz,

Synchronous Step Down DC/DC Converter

 

 

EC3293A

 

 

General Description

 

The ​​ EC3293A ​​ 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 ​​ EC3293A ​​ 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 ​​ EC3293A ​​ requires ​​ a ​​ minimal ​​ number ​​ of ​​ readily available, standard external components and is available in a space-saving TSOT23-6L package.

 

Features

​​ 4.7V to 18V input voltage

​​ Output adjustable from 0.8V to 15V

​​ Output current up to 3A

​​ Integrated 110mΩ/58mΩ 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

GND

Ground.

2

SW

Power switching output.

3

IN

Power input.

4

FB

Feedback input.

5

EN

Enable input.

6

BOOT

High-side gate drive boost input.

 

 

 

 

 

 

 

 

 

Application Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: R5 and C7 are optional.

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ R3=40.2KΩ for T-type

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ R3=0Ω for voltage division

 

Ordering Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

 

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 ……...…………...…….…4.75V to 18V

Output Voltage VOUT ……...…………... ​​ 0.923V 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 =1V

 

0.7

 

mA

Feedback Voltage

VFB

4.75V  VIN  18V

0.776

0.8

0.824

V

Feedback Over-voltage Threshold

 

 

 

0.88

 

V

Error Amplifier Voltage Gain *

AEA

 

 

1000

 

V/V

High-Side Switch-On Resistance *

RDS(ON)1

 

 

110

 

Low-side Switch-On Resistance *

RDS(ON)2

 

 

58

 

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

100

125

150

KHz

Maximum Duty Cycle

DMAX

VFB = 0.5V

 

90

 

%

Minimum On Time *

 

 

 

120

 

ns

EN Falling Threshold Voltage

 

VEN Falling

 

1.22

 

V

EN Rising Threshold Voltage

 

VEN Rising

 

1.32

 

V

Input Under Voltage Lockout Threshold

 

VIN Rising

 

3.75

 

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 12V→3.3V (Load 1A)Shut Down (Iout 1A→Shut down)

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Ripple (12V => 3.3V, Load=2A)Output Ripple (12V => 3.3V, Load=1A)

 

 

 

 

 

 

 

 

 

 

 

 

 

Output Ripple (12V => 3.3V, Load=0A)Dynamic Load (Iload=0.2A_1.2A;Vout=3.3V)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Short Circuit Protection

 

 

 

 

 

 

 

 

 

 

 

 

Efficiency         ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Efficiency

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Application Information

Overview

The EC3293A 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 3A of load current.

The ​​ EC3293A ​​ 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  ​​​​ EC3293A  ​​​​ FB  ​​​​ pin  ​​​​ exceeds  ​​​​ 10%  ​​​​ of  ​​​​ the nominal ​​ regulation ​​ voltage ​​ of ​​ 0.8V, ​​ 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 4.7V ​​ 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 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 0.8V.

 

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/0.8V-1)

Use T-type network for when Vout is low.

 

 

 

 

 

 

 

 

Figure 1:T-type network

 

 

 

 

 

 

 

 

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

 

VOUT (V)

R1 (KΩ)

R2 (KΩ)

Rt (KΩ)

LOUT (μH)

COUT (μF)

1.05

10

32.4

150

2.2

44

1.2

20.5

41.2

120

2.2

44

1.8

40.2

32.4

75

3.3

44

2.5

40.2

19.1

59

4.7

44

3.3

40.2

13

40.2

6.8

44

5

40.2

7.68

24.9

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 EC3293A 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 EC3293A

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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