DC1977A - Demo Manual

DEMO MANUAL
DC1977A-A/B
LTC4121EUD/LTC4121EUD-4.2
400mA Synchronous Buck
Battery Charger
Description
Demonstration circuit 1977A is the demonstration board
for LTC®4121EUD-4.2/LTC4121EUD, a 400mA Synchronous Buck Battery Charger. The DC1977A supports the
Maximum Power Point Tracking (MPPT) feature on the
LTC4121EUD, for use with Photovoltaic (PV) cells or
highly resistive sources.
batteries with the maximum power available from the PV
cell. It is also used if the power supply is highly resistive, such as applications that are at the end of very long
wire runs.
Design files for this circuit board are available at
http://www.linear.com/demo
FEATURED PART
DC1977A-A
LTC4121EUD-4.2 (Fixed Output)
DC1977A-B
LTC4121EUD (Adjustable Output)
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
The LTC4121EUD is typically used with PV cells to charge
Performance Summary
Specifications are at TA = 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
IN
DC1977A Input Voltage
I(IN) < 800mA
4.4
40
V
PVIN
DC1977A PV Cell Input
I(IN) < 800mA
5
40.5
V
V(BAT)
DC1977A BAT Pin Voltage
RFB2 = 1.40MΩ, RFB1 = 1.05MΩ
2.4
4.25
V
I(BAT)
DC1977A BAT Pin Current
V(BAT) = 3.7V, DC1977A(R5) = 3.01kΩ, JP1 (“MPPT”) = ‘OFF’
370
400
mA
385
MAX
UNITS
Typical Application
LTC4121 Efficiency vs VIN at VFLOAT = 8.4V
High Efficiency, Wide Input Voltage Range Charging with LTC4121
RMPPT1
787k
+
–
VIN
VBAT + 200mV
TO 40V
RPROG
3.01k
LTC4121
FB
FREQ
GND
FBG
RFB1
1.05M
RFB2
1.40M
200mA, PROG = 6.04k
400mA, PROG = 3.01k
95
SW
CHGSNS
BAT
PROG
CINTVCC
2.2µF
CBOOST
22nF
LPS4018-333ML
MPPT
RMPPT2
121k
97
INTVCC
BOOST
CBAT
47µF
EFFICIENCY (%)
CIN
10µF
IN
RUN
93
91
89
+
Li-Ion
87
dc1977a F01
VBAT = 8.3V
5
10
15
20
25
VIN (V)
30
35
40
dc1977afa
1
DEMO MANUAL
DC1977A-A/B
assembly test Procedure
Refer to Figure 1 for the proper measurement equipment
setup and jumper settings and follow the procedure below. .
4.Turn PS2 off, move connection to point B, and turn PS2
on.
NOTE. When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the VCC
or VIN and GND terminals. See Figure 2 for proper scope
probe technique.
5.Verify that VM1 indicates less than 4V, and then verify
that AM1 indicates between 380mA ~ 400mA. Verify
that VM2 shows 2.15V ~ 3.5V. 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.
6.Turn PS2 off, move connection to Point C, and turn PS2
on.
2.Connect PS2 to point A, set to 15V and turn on.
3.Verify that VM1 indicates less than 4V, and then verify
that AM1 indicates 380mA ~ 400mA. Verify that VM2
shows 14V ~ 14.5 V. There is only a series diode between
PV+ and the VIN pin of the LTC4121. The purpose of this
diode is prevent backfeeding a PV cell, if connected.
A single diode Vf is insufficient to activate the MPPT
feature, and the LTC4121 delivers full charge current
to the battery.
–
C
AM2
–
B
82.4Ω
2W
7.Verify that VM1 indicates less than 4V, and then Verify
that AM1 indicates 100mA ~150mA. Verify that VM2
shows 10V ~ 11V. The source impedance of the power
supply is now 98Ω. The MPPT feature has engaged and
the charge delivered to the battery has been reduced
to allow VIN to stay at the programmed MPPT point.
8.Set JP1 (“MPPT”) to ‘OFF’, test is finished.
15.8Ω
2W
+
+
+
PS2
15V POWER SUPPLY
0.25A
–
A
VM2
–
–
+
–
+
PS1
3.6V POWER SUPPLY
1A
–
AM1
3.6Ω
+
VM1
–
Figure 1. DC1977A Equipment Setup
2
dc1977afa
DEMO MANUAL
DC1977A-A/B
assembly test Procedure
Figure 2. Measuring Input or Output Ripple
Note: All connections from equipment should be Kelvin connected directly to the board pins
which they are connected on this diagram and any input or output leads should be twisted pair.
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 for stable operation.
LTC4121EUD ENABLE
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 (see schematic) ensure that the LTC4121 is not
enabled until VIN is greater than 4.4V.
Buck Charger
The heart of the LTC4121EUD is the buck topology charger.
The buck topology charger is a synchronous current mode
regulator with N-channel FETs. The use of N-channel FETs
optimizes die area, and only requires a single external
0.022µF capacitor for boostrapping the high side gate drive.
The LTC4121EUD can charge up to 4 Li-Ion batteries
in series, and has a maximum float voltage of 18V. The
LTC4121EUD-4.2 is optimized for charging a single Li-Ion
battery, and has a fixed float voltage of 4.2V.
The buck inductor does not terminate in a capacitor, as in
a buck voltage regulator, but rather goes through a small
on-die metal 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 Rprog. On the
DC1977A, Rprog = 3.01kΩ, so I(BAT) = 400mA, if the
MPPT function does not reduce the current.
The buck regulator thus acts as a current source when
the battery is in the constant current (CC) charging region
and as a classic voltage output buck regulator when the
battery is in the constant voltage (CV) charging region.
In the constant voltage region, the battery becomes the
output capacitor. If no battery is present, please ensure
that the capacitors documented in the data sheet are
installed on the board, to provide charge storage for the
buck regulator.
The battery charge current is programmed by Rprog =
3.01kΩ. The equation for battery charge current is:
R_prog = h_prog • (V_prog/I_(chg)) = 988 • 1.227V/0.4
= 3.01kΩ
dc1977afa
3
DEMO MANUAL
DC1977A-A/B
theory of operation
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.
Figure 3 shows various nodes of interest with VIN = 5V,
and the switching frequency at 750kHz (T = 1.333µs), The
duty cycle is 86% for V(BAT) = 3.6V, this is 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 making the effective output of the
buck regulator the voltage necessary to push 400mA into
the battery. This “effective” voltage is 5 X 0.86 = 4.3V,
is the voltage necessary to ensure that a 400mA average
current is flowing through the on-die metal sense resistor.
Figure 4 shows the same nodes as Figure 3, but with VIN =
40V, and still at 750kHz. The 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 “effective” output voltage of 4.3V, so that the battery charges
at 400mA.
Figure 3. Normal Operation, Zoom, VIN = 5.1V, DK. Blue = VIN,
Grn = ICHARGE, LT. Blue = VSW, Pk. = INTVCC, 750kHz
Maximum Power Point Tracking (MPPT)
The LTC4121EUD provides a Maximum Power Point Tracking (MPPT) function for use with PV cells or highly resistive
power supplies. The MPPT pin allows programming of the
MPPT point as a percentage of the Open Circuit VIN (VOC).
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 VIN. To enable set the MPPT point as
a fraction of VOC, based on the equation:
Figure 4. Normal Operation, Zoom, VIN = 40V, DK. Blue = VIN,
Grn = ICHARGE, LT. Blue = VSW, Pk. = VBOOST, 750kHz
VMPPT
0.1(k +1)
=[
]
VOC
k
where RMPPT2 = k • RMPPT1. So for the demo board, k =
121/787 = 0.154, and VMPPT/VOC = 0.75 • VOC. When MPPT
is enabled (not equal to VIN), the LTC4121EUD periodically
disconnects the load, and measures VIN no load = VOC. It
then increases the load on VIN to meet charger demand,
until the VMPPT threshold is reached, after which it no
4
dc1977afa
DEMO MANUAL
DC1977A-A/B
theory of operation
longer increases the load. This allows the MPPT voltage
divider to set the desired MPPT point as a percentage of
the no load VIN:
Figure 5 shows the LTC4121EUD operating into a source
impedance of 98Ω so the LTC4121 draws more power from
VIN than is available. The MPPT pin of the LTC4121EUD
sets the MPPT point to 0.75 of the open circuit voltage.
First VOC is determined by removing all loads and letting
VIN rise to VOC. The power drawn from VIN is increased until
the VIN falls to the MPPT point, 0.75 • VOC = 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 6 shows the same system, but the source impedance
was lowered to 16Ω, consequently the full power needed
to meet the requirements of Rprog is available before VIN
falls to the MPPT voltage.
Figure 5. MPPT Test, DK. Blue = VIN (Through 98Ω), Green = IL,
LT. Blue = V(SW), k = 0.15, VMPPT/VOC = 0.75
Battery capacitors C1 and C2
The maximum float voltage for the LTC4121EUD is 18V,
but for the LTC4121EUD-4.2, it is 4.2V. Linear recommends 47µF of capacitance on the BAT pin, if the battery
is missing. 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 as a no load.
Figure 6. MPPT Test, DK. Blue = VIN (Through 16Ω), Green = IL,
LT. Blue = V(SW), k = 0.15, VMPPT/VOC = 0.75
dc1977afa
5
DEMO MANUAL
DC1977A-A/B
Parts List
ITEM
QTY REFERENCE
DC1977A General Bill of Materials
Required Circuit Components
1
1
C3
2
1
C4
3
1
C5
4
1
L1
5
1
R1
6
1
R2
7
1
R3
8
1
R4
9
1
R7
Additional Demo Board Circuit Components
1
1
D1
2
1
M1
3
2
R5, R9
4
1
R6
5
2
R8, R10
6
1
R13
7
1
R14
8
1
R15
Hardware: For Demo Board Only
1
7
E1, E2, E3, E6, E7, E10, E11
2
3
4
5
4
0
4
4
E4, E5, E8, E9
J1-OPT
JP1-JP4
JP1-JP4
ITEM
QTY REFERENCE
DC1977A-A Bill of Materials
Required Circuit Components
1
0
R11
2
1
R12
3
1
U1
Additional Demo Board Circuit Components
1
1
C1
2
0
C2
ITEM
QTY REFERENCE
DC1977A-B Bill of Materials
Required Circuit Components
1
1
R11
2
1
R12
3
1
U1
Additional Demo Board Circuit Components
1
2
C1, C2
6
PART DESCRIPTION
MANUFACTURER/PART NUMBER
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
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
DIODES, DFLS240L
VISHAY, Si2343CDS
VISHAY, CRCW040210K0FKED
VISHAY, CRCW04022K00JNED
VISHAY, CRCW04020000Z0ED
VISHAY, CRCW040247K0JNED
VISHAY, CRCW04025K10JNED
VISHAY, CRCW0402100KJNED
TURRET, 0.09 DIA
MILL-MAX, 2501-2-00-80-00-00-07-0
TURRET, 0.061"
CONN, 3 Pin Polarized
HEADER, 3 Pin, SMT, 2mm
SHUNT, 2mm
MILL-MAX, 2308-2-00-80-00-00-07-0
HIROSE, DF3-3P-2DSA
SULLIN, NRPN031PAEN-RC
SAMTEC, 2SN-BK-G
PART DESCRIPTION
MANUFACTURER/PART NUMBER
No Load
RES, CHIP, 0Ω jumper, 1/16W, 0402
40V 400mA SYNCHRONOUS STEP-DOWN BATTERY
CHARGER, 3mm × 3mmQFN16
VISHAY, CRCW04020000Z0E
LINEAR TECH., LTC4121EUD-4.2#PBF
CAP, CHIP, X5R, 47µF, ±10%, 16V, 1210
CAP, CHIP, X5R, 47µF, ±10%, 16V, 1210
MURATA, GRM32ER61C476KE15L
MURATA, GRM32ER61C476KE15L
PART DESCRIPTION
MANUFACTURER/PART NUMBER
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
CAP, CHIP, X5R, 47µF, ±10%, 16V, 1210
MURATA, GRM32ER61C476KE15L
dc1977afa
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
2
3
4
E2
E1
PROG
NTC
E5
E4
PV- or Vin-
E3
4.4V - 40V
0.4A
Vin+
PV+
R6
2.0k 5%
4
4
D1
DFLS240L
ON
OFF
MPPT
JP1
R2
121k
R1
787k
JP4
EXT
NTC
INT
R9
10.0k
R8
0 Ohm
JUMPER
FREQ
RUN
ENABLED
DISABLED
3
1.5 MHz
10.0k 750 kHz
R5
INTVCC
R4
324k
R3
261k
3
JP3
JP2
R7
3.01k
BATSNS/FB
PROG
10
13
5
GND
3
IN
17
EPAD
2
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
R15
100k
5%
GEORGE B.
SCALE = NONE
NC
PCB DES.
APP ENG.
DATE:
N/A
SIZE
7 - 9- 14
IC NO.
R12
1.05M
0 Ohm
C1
C2*
C2
OPEN
CHRG
FAULT
GND
1
SHEET 1
LTC4121EUD - 4.2 / LTC4121EUD
DEMO CIRCUIT 1977A - A / B
OF
1
3
REV.
40V 400mA SYNCHRONOUS STEP-DOWN
BATTERY CHARGER
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900 www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
BAT
GND
ENTC
J1 OPT
DF3-3P-2DSA
R10
0 Ohm
JUMPER
1
2
3
BAT
2.7V - 18V
400mA
E6
GND
E7
E8
E9
E10
VIN
4.4V - 40V
GEORGE B.
E11
DATE
7 - 9- 14
APPROVED
22µF/25V 22µF/25V
47µF/16V
TECHNOLOGY
1.40M
TITLE: SCHEMATIC
LTC4121EUD
R11
OPEN
*
C1
R12 TO BE CONNECTED TO C2 & C3
PRODUCTION FAB
3
1
DESCRIPTION
REVISION HISTORY
REV
U1
R12 *
R13
47k
5%
-
ECO
LTC4121EUD - 4.2
APPROVALS
-B
ASSY
-A
*
R14
5.1k
5%
M1
Si2343DS
C5
2.2µF
20%
6.3V
INTVCC
R11 *
L1
33.0uH
25V
C3
0.022µF
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
CUSTOMER NOTICE
11
9
NC/FBG
8
BAT
4
1
2
15
14
CHGSNS
sw
INTVcc
BOOST
FAULT
CHRG
UNLESS NOTED:
RESISTORS: OHMS, 0402, 1%, 1/16W
CAPACITORS: uF, 0402, 10%, 50V
NTC
MPPT
FREQ
RUN
12
6
7
16
U1
LTC4121EUD-4.2 / LTC4121EUD
C4
10µF
50V
1210
2
1
2
3
4
DEMO MANUAL
DC1977A-A/B
Schematic Diagram
dc1977afa
7
DEMO MANUAL
DC1977A-A/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
Copyright © 2004, Linear Technology Corporation
8
dc1977afa
Linear Technology Corporation
LT 1214 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2014
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