LTC4121EUD-4.2_技术文档

DEMO MANUAL

DC1977A-A/DC1977A-B

LTC4121EUD/LTC4121EUD-4.2

400mA Synchronous Buck

Battery Charger

Description

The LTC4121 and LTC4121-4.2 feature constant-current–

constant-voltage charging capability suitable for lithium-

ion or lead-acid cells. The LTC4121-4.2 supports charging

a single lithium-ion cell with a cell voltage of 4.2V. The

LTC4121 may be programmed to charge battery voltages

up to 18V with a resistive divider.

DC1977A-A

DC1977A-B

LTC4120EUD-4.2 (Fixed Output)

LTC4121EUD (Adjustable Output)

Demonstration Board DC1977A showcases the

LTC4121-4.2 and LTC4121 40V, 400mA synchronous-

buck battery charger integrated circuit. The DC1977A

supports the maximum-power-point tracking (MPPT)

feature of the LTC4121EUD to optimize power delivery

from photovotalic cells or highly resistive sources.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1977

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog

Devices, Inc. All other trademarks are the property of their respective owners.

performance summary ^{Specifications are at T}_A^{= 25°C}

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Note: Reference designators refer to Schematic on p. 7.

IN

DC1977A Input Voltage

DC1977A PV Cell Input

DC1977A BAT Pin Voltage

DC1977A BAT Pin Current

I(IN) < 800mA

4.4

5

40

V

PV

I(IN) < 800mA

40.5

4.25

421

IN

V(BAT)

I(BAT)

R11 = 1.40MΩ, R12 = 1.05MΩ

V(BAT) = 3.7V; DC1977A; (R7) = 3.01kΩ; JP1 (“MPPT”) = ‘OFF’

2.5

383

V

402

mA

Demo BoarD application

High Efficiency, Wide Input Voltage Range Charging with LTC4121

LTC4121 Efficiency vs V_IN

100

95

90

85

80

75

70

INTV

BOOST

IN

CC

R

= 6.04k

PROG

C

2.2µF

C

10µF

INTVCC

IN

R

261k

= 3.01k

RUN1

C

22nF

BOOST

RUN

MPPT

LPS4018-333ML

R

324k

R

MPPT1

RUN2

LTC4121

787k

SW

CHGSNS

R

121k

MPPT2

BAT

R

FB1

1.05M

V

IN

BAT

C

BAT

47µF

+

+ 200mV

TO 40V

–

FB

R

FB2

1.40M

PROG

+

FREQ

GND

FBG

R

PROG

3.01k

Li-Ion

V

= 4.1V

BAT

5

10

15

20

25

(V)

30

35

40

dc1977a F01

V

IN

DC1977A F02

dc1977afb

1

DEMO MANUAL

DC1977A-A/DC1977A-B

assemBly test proceDure

Refer to Figure 1 for the proper measurement equipment

setup and jumper settings and follow the procedure below.

5. Verify that VM1 indicates 3.3V to 3.9V, and then verify

that AM1 indicates 387mA to 417mA. Verify that VM2

shows 12.6V to 13.2. The source impedance of the

power supply is now ≈ 16Ω. But this impedance still

allows delivering full charge current without engaging

the MPPT feature.

1. Set JP1 (“MPPT”) to ‘ON’, set PS1 to 3.6V and turn

on.

2. Connect PS2 to point A, set to 15V and turn on.

3. Verify that VM1 indicates 3.3V to 3.9V, and then verify

that AM1 indicates 387mA to 417mA. Verify that VM2

6. Turn PS2 off, move connection to Point C, and turn

PS2 on.

shows 14.5V to 15.1V. There is only a series diode

7. Verify that VM1 indicates 3.3V to 3.9V, and then Verify

that AM1 indicates 105mA to 115mA. Verify that VM2

shows 10.6V to 11.3V. The source impedance of the

power supply is now 98Ω. The MPPT feature has

engaged and the charge delivered to the battery has

+

between PV and the V pin of the LTC4121. The

IN

purpose of this diode is prevent backfeeding a PV

cell, if connected. A single diode V is insufficient to

f

activate the MPPT feature, and the LTC4121 delivers

full charge current to the battery.

been reduced to allow V to stay at the programmed

IN

4. Turn PS2 off, move connection to point B, and turn

PS2 on.

MPPT point.

8. Set JP1 (“MPPT”) to ‘OFF’, test is finished.

C

B

82.4Ω

2W

15.8Ω

2W

AM2

–

+

VM2

+

–

PS2

15V POWER SUPPLY

0.25A

A

–

+

AM1

+

VM1

–

+

PS1

3.6Ω

3.6V BIPOLAR SUPPLY

1A

–

DC1977a F03

Figure 1. DC1977A Equipment Setup

Note: All connections from equipment should be kelvin-connected directly to the board pins

which they are connected on this diagram. All input or output leads should be twisted pair.

dc1977afb

2

DEMO MANUAL

DC1977A-A/DC1977A-B

theory of operation

The LTC4121EUD-4.2/LTC4121EUD is a 4.4V ~ 40V input

buck topology battery charger with maximum power point

tracking (MPPT) for use with PV cells or highly resistive

power supplies. The buck-topology charger uses current

mode control for stable operation.

The buck regulator acts as a current source when the

battery is in the constant-current charging region and as

a classic voltage output buck regulator when the battery

is in the constant-voltage charging region.

The battery charge current is programmed by

R

= 3.01kΩ. The equation for R

is:

1.227V

0.4

PROG

LTC4121EUD ENABLE

V

PROG

R

_PROG= h_PROG

•

= 986 •

= 3.01kΩ

I_CHG

The LTC4121 can be enabled or disabled via the RUN pin,

and this functionality can be accessed via JP2, the RUN

jumper. When JP2 is in the “ENABLE” position, R3 and

R4 ensure that the LTC4121 is not enabled until Vin is

greater than 4.4V.

The LTC4121EUD provides a switching frequency select

pin, FREQ, to select between 750kHz and 1.5MHz; this

function is accessed by JP4, the “FREQ” jumper.

Note: Do not float the LTC4121 FREQ pin. Operate the

demo board with JP3 in either the 750kHz or 1.5MHz

position.

Note: Do not float the LTC4121 RUN pin. Operate

the demo board with JP2 in either the DISABLED or

ENABLED position.

Figure 2 shows various nodes of interest with V = 5V,

IN

Buck Charger

and the switching frequency at 750kHz (T = 1.333µs), The

duty cycle is 86% for V(BAT) = 3.6V, not the 72% duty

expected from a buck regulator. When the battery voltage

is 3.6V, the charger is in constant-current mode, so the

control loop is forcing the output of the buck regulator

to the voltage necessary to push 400mA into the battery.

This “effective” voltage, 5 • 0.86 = 4.3V, is the voltage

necessary to ensure that a 400mA average current is flow-

ing through the on-die sense resistor.

The heart of the LTC4121EUD is the buck-topology bat-

tery charger. The buck-topology charger is a synchronous,

current-mode-control regulator with N-channel FETs. The

use of N-channel FETs minimizes conduction losses, and

requires only a single external 0.022µF capacitor to gener-

ate the high-side gate drive.

The LTC4121EUD can charge up to four Li-Ion cells in

series, and supports a maximum battery voltage of 18V.

The LTC4121EUD-4.2 is optimized for charging a single

Li-Ion cell to a fixed cell voltage of 4.2V.

Figure 3 shows the same nodes as Figure 2, but with

V

= 40V. The switching frequency is still 750kHz. The

IN

duty cycle is ≈ 200ns/1.333µs, or 15%, but the period is

2.7µs. This is because the LTC4121 minimum on time was

greater than that needed to achieve 4.3V, and the LTC4121

starts to pulse skip to get the necessary average duty

cycle. The average duty cycle is 300ns/2.667µs = 11%.

This produces an output voltage of 4.3V, so the battery

still charges at 400mA.

The current in the buck inductor passes through a small

on-die resistor for current measurement, and then goes

back out to the BAT pin. The battery is connected to the

BAT pin; this allows the LTC4121EUD to measure not only

the cycle-by-cycle current, but also the average current.

The cycle-by-cycle current is used by the current-mode

buck regulator, and the average current is the battery

charge current as programmed by R

. On DC1977A,

PROG

Maximum Power Point Tracking (MPPT)

R

= 3.01kΩ, so I(BAT) = 402mA provided that the

PROG

The LTC4121EUD provides a maximum-power-point

tracking (MPPT) function for use with PV cells or highly

MPPT function does not reduce the current.

dc1977afb

3

DEMO MANUAL

DC1977A-A/DC1977A-B

theory of operation

resistive power supplies. The MPPT pin allows program-

ming of the MPPT point as a percentage of the open-

circuit V_IN(V_OC). To access this functionality the demo

board provides JP1, the “MPPT” jumper, and R1 and R2.

It is important to note that the disabled position for MPPT

is the MPPT pin at V_IN. To enable MPPT, set the MPPT

point as a fraction of V_OC. See the discussion in Maximum

Power Point Tracking section of the LTC4121 data sheet.

When MPPT is enabled (not equal to V_IN), the LTC4121EUD

periodically disconnects the load from the power source,

and measures V with no load = V . It then increases

IN

OC

the load on V to meet charger demand until the V

IN

MPPT

threshold is reached, after which it no longer increases

the load. This allows the MPPT voltage divider to set the

Figure 2. Normal Operation, Zoom, V_IN= 5.1V, DK. Blue = V_IN,

Grn = I_CHARGE, LT. Blue = V_SW, Pk. = INTV_CC, 750kHz

desired MPPT point as a percentage of V with no load.

IN

Figure 4 shows the LTC4121EUD operating from a source

impedance of 98Ω. The MPPT pin of the LTC4121EUD

sets the MPPT point to 0.75 of the open-circuit voltage.

First, V is determined by removing all load and letting

OC

V

IN

rise to V . The power drawn from V is increased

until the voltage at V falls to the MPPT point, 0.75 • V

OC IN

IN

OC

= 0.75 • 15V = 11.25V. The resolution of the MPPT DAC

is 330mV, thus this example has the MPPT point at

11V. The LTC4121 stops drawing power at this point, and

the charge current (green) never exceeds 200mA, even

though the Rprog value was chosen for 400mA.

Figure 5 shows the same system, but the source imped-

ance was lowered to 16Ω. Consequently, the full power

needed to meet the requirements of the programmed

charge current is available before V falls to the MPPT

IN

voltage.

Figure 3. Normal Operation, Zoom, V_IN= 40V, DK. Blue = V_IN,

Grn = I_CHARGE, LT. Blue = V_SW, Pk. = V_BOOST, 750kHz

dc1977afb

4

DEMO MANUAL

DC1977A-A/DC1977A-B

theory of operation

Battery capacitors C1 and C2

The maximum battery voltage for the LTC4121EUD is

18V, and for the LTC4121EUD-4.2, it is 4.2V. Analog

Devices recommends 47µF of capacitance on the BAT

pin, if the battery is not present. For the LTC4121EUD

the voltage rating of the capacitor will need to be 25V, so

two 22µF, 25V, MLCC capacitors are used. In the case of

the LTC4121EUD-4.2, a 6.3V capacitor will suffice, and

a single 47µF, 6.3V, MLCC capacitor is used for C1, with

C2 not placed.

Reverse-Blocking Circuit

Components Q1, R16 and C6 comprise a reverse-blocking

circuit. The circuit performs two functions. First, the cir-

cuit prevents the battery from back-charging the power

source when the power source is dormant (e.g., a solar

cell in the absence of illumination). Note that this func-

tionality can also be provided through D1. Second, when a

charged battery is connected to the circuit in the absence

of input voltage, current will flow from the battery into the

BAT pin and out the IN pin, charging C4. With battery volt-

ages in excess of ~10V, this current surge can destroy the

device. Note that this is not a problem when only one or

two series Li-Ion cells are employed. Thus, this reverse-

blocking circuit may not be necessary depending on the

application. If reverse-blocking is not required, C6 and

R16 also become unnecessary. These two components

provide a path to the BAT pin from which the LTC4121

derives bias for internal circuits which would be provided

by the battery directly in the absence of Q1. See, for exam-

ple, the application on the first page of this manual.

Figure 4. MPPT Test, DK. Blue = V_IN(Through 98Ω), Green = I_L,

LT. Blue = V(SW), k = 0.15, V_MPPT/V_OC= 0.75

Figure 5. MPPT Test, DK. Blue = V_IN(Through 16Ω), Green = I_L,

LT. Blue = V(SW), k = 0.15, V_MPPT/V_OC= 0.75

dc1977afb

5

DEMO MANUAL

DC1977A-A/DC1977A-B

parts list

ITEM

QTY REFERENCE

PART DESCRIPTION

MANUFACTURER/PART NUMBER

DC1977A General Bill of Materials

Required Circuit Components

1

2

3

4

5

6

7

8

9

1

C3

C4

C5

L1

R1

R2

R3

R4

R7

CAP, CHIP, X7R, 0.022µF, 10%, 50V, 0402

CAP, CHIP, X5R, 10µF, 10%, 50V, 1210

CAP, CHIP, X5R, 2.2µF, 20%, 6.3V, 0402

IND, SMT, 33µH, 420mΩ, 20%, 0.80A, 4mm × 4mm

RES, CHIP, 787kΩ, 1%, 1/16W, 0402

RES, CHIP, 121kΩ, 1%, 1/16W, 0402

RES, CHIP, 261kΩ, 1%, 1/16W, 0402

RES, CHIP, 324kΩ, 1%, 1/16W, 0402

RES, CHIP, 3.01kΩ, 1, 1/16W, 0402

TDK, C1005X7R1E223K

TAIYO-YUDEN, UMK325BJ106KM-T

MURATA, GRM155R60J225ME15D

COILCRAFT, LPS4018-333ML

VISHAY, CRCW0402787KFKED

VISHAY, CRCW0402121KFKED

VISHAY, CRCW0402261KFKED

VISHAY, CRCW0402324KFKED

VISHAY, CRCW04023K01FKED

Additional Demo Board Circuit Components

1

2

3

4

5

6

7

8

9

1

2

1

2

1

C6

D1

M1

R5, R9

R6

R8, R10

R13

R14

R15

R16

CAP, CHIP, X5R, 4.7µF, 20%, 6.3V, 0603

DIODE, SCHOTTKY, 40V, 2A, PowerDI123

MOSFET, P-Channel, –30V, –5.9A, 45mΩ, SOT-23

RES, CHIP, 10kΩ, 1%, 1/16W, 0402

RES, CHIP, 2kΩ, 5%, 1/16W, 0402

RES, CHIP, 0Ω jumper, 1/16W, 0402

RES, CHIP, 47kΩ, 5%, 1/16W, 0402

RES, CHIP, 5.1kΩ, 1%, 1/16W, 0402

RES, CHIP, 100kΩ, 5%, 1/16W, 0402

RES, CHIP, 464kΩ, 1%, 1/10W, 0603

MURATA, GRM188R60J475KE19D

DIODES, DFLS240L

VISHAY, Si2343CDS

VISHAY, CRCW040210K0FKED

VISHAY, CRCW04022K00JNED

VISHAY, CRCW04020000Z0ED

VISHAY, CRCW040247K0JNED

VISHAY, CRCW04025K10JNED

VISHAY, CRCW0402100KJNED

YAGEO, RC0603FR-07464KL

10

Hardware: For Demo Board Only

1

7

E1, E2, E3, E6, E7, E10, E11 TURRET, 0.09 DIA

MILL-MAX, 2501-2-00-80-00-00-07-0

2

3

4

5

4

0

4

E4, E5, E8, E9

J1-OPT

JP1-JP4

TURRET, 0.061"

MILL-MAX, 2308-2-00-80-00-00-07-0

HIROSE, DF3-3P-2DSA

SULLIN, NRPN031PAEN-RC

SAMTEC, 2SN-BK-G

CONN, 3 Pin Polarized

HEADER, 3 Pin, SMT, 2mm

SHUNT, 2mm

JP1-JP4

ITEM

QTY REFERENCE

PART DESCRIPTION

MANUFACTURER/PART NUMBER

DC1977A-A Bill of Materials

Required Circuit Components

1

2

3

0

1

R11

R12

U1

DO NOT INSTALL

RES, CHIP, 0Ω jumper, 1/16W, 0402

40V 400mA SYNCHRONOUS STEP-DOWN BATTERY

CHARGER, 3mm × 3mmQFN16

VISHAY, CRCW04020000Z0E

LINEAR TECH., LTC4121EUD-4.2#PBF

1

2

1

0

C1

C2

CAP, CHIP, X5R, 47µF, 10%, 16V, 1210

MURATA, GRM32ER61C476KE15L

ITEM

QTY REFERENCE

PART DESCRIPTION

MANUFACTURER/PART NUMBER

DC1977A-B Bill of Materials

Required Circuit Components

1

2

3

1

R11

R12

U1

RES, CHIP, 1.40MΩ, 1%, 1/16W, 0402

RES, CHIP, 1.05MΩ, 1%, 1/16W, 0402

40V, 400mA SYNCHRONOUS STEP-DOWN BATTERY

CHARGER, 3mm × 3mmQFN16

VISHAY, CRCW04021M40FKE

VISHAY, CRCW04021M05FKED

LINEAR TECH., LTC4121EUD#PB

1

2

C1, C2

CAP, CHIP, X5R, 47µF, 10%, 16V, 1210

MURATA, GRM32ER61C476KE15L

dc1977afb

6

DEMO MANUAL

DC1977A-A/DC1977A-B

schematic Diagram

dc1977afb

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

7

DEMO MANUAL

DC1977A-A/DC1977A-B

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:

This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT

OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete

in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety

measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union

directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.

If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date

of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU

OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS

FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR

ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims

arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all

appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or

agency certified (FCC, UL, CE, etc.).

No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,

customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.

Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and

observe good laboratory practice standards. Common sense is encouraged.

This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application

engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

dc1977afb

LT 0817 REV B • PRINTED IN USA

8

 LINEAR TECHNOLOGY CORPORATION 2014


型号：	LTC4121EUD-4.2
厂家：	Linear
描述：	400mA Synchronous Buck Battery Charger 电池
文件：	总8页 (文件大小：1371K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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