EC3292A|2A,18V,500KHz,Syn. Step-Down Converter


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EC3292A

 ​​ ​​ ​​ ​​​​ 2A, 18V, 500KHz, 

 ​​ ​​ ​​ ​​ ​​​​ Synchronous StepDown DC/DC Converter

 

 

 

 

General Description

 

 

The EC3292A 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 wide input supply range, with excellent

load and line regulation. 

The EC3292A 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 EC3292A 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 0.8V to 15V

  Output current up to 2A

  Integrated 160mΩ/85mΩ 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

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.

Details please see the DVT report.

 

Ordering Information

 

 

Part Number

Package

Marking

Marking Information

EC3292ANT3R

TSOT23-6

​​ 3292A

LLLLL

  • LLLLLLot No

 

 

 

 

 

 

 

 

 

 

 

 

 

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 ……...…………...…….…4.7V to 18V

Output Voltage VOUT ……...…………... ​​ 0.8V 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 =0.85V

 

0.09

 

mA

Feedback Voltage

VFB

4.7V  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

 

 

160

 

Low-side Switch-On Resistance *

RDS(ON)2

 

 

85

 

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

 

1.22

 

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 = 10μF 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 ProtectionEfficiency(L=4.7uA)

​​ 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Application Information

 

Overview

 

The EC3292A 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 ​​ EC3292A ​​ 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  ​​​​ EC3292A  ​​​​ 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.

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 EC3292A 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.

 

 

 

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 anexternalSchottky diode

between IN and BOOT pins, as shown in Figure 2.

 

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.

 

 

L1

R1

R2

C2

Vout = 5.0V

6.8μH

40.2K

7.68K

10μF×2

Vout = 3.3V

4.7μH

40.2K

13K

10μF×2

Vout = 2.5V

3.3μH

40.2K

19.1K

10μF×2

Vout = 1.8V

2.2μH

40.2K

32.4K

10μF×2

Vout = 1.2V

2.2μH

20.5K

41.2K

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 EC3292A

 

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

 

 ​​ ​​ ​​ ​​​​ 2A, 18V, 500KHz, 

 ​​ ​​ ​​ ​​ ​​​​ Synchronous StepDown DC/DC Converter

 

EC3292T

 


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