LTC4121/LTC4121-4.2
40V 400mA Synchronous
Step-Down Battery Charger
FEATURES
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DESCRIPTION
The
LTC
®
4121
is a 400mA constant-current/constant-
voltage (CC/CV) synchronous step-down battery charger.
In addition to CC/CV operation, the LTC4121 regulates its
input voltage to a programmable percentage of the input
open-circuit voltage. This technique maintains maximum
power transfer with high impedance input sources such
as solar panels.
An external resistor programs the charge current up to
400mA. The LTC4121-4.2 is suitable for charging Li-Ion/
Polymer batteries, while the programmable float voltage
of the LTC4121 is suitable for several battery chemistries.
The LTC4121 and LTC4121-4.2 include an accurate RUN
pin threshold, low voltage battery preconditioning and bad
battery fault detection, timer termination, auto-recharge,
and NTC temperature qualified charging. The
FAULT
pin
provides an indication of bad battery or temperature faults.
Once charging is terminated, the LTC4121 signals end-of-
charge via the
CHRG
pin, and enters a low current SLEEP
mode. An auto-restart feature starts a new charging cycle
if the battery voltage drops by 2.2%.
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Wide Input Voltage Range: 4.4V to 40V
Temperature Compensated Input Voltage
Regulation for Maximum Power Point Tracking
(MPPT)
Adjustable Float Voltage 3.5V to 18V (LTC4121)
Fixed 4.2V Float Voltage Option (LTC4121-4.2)
High Efficiency: Up to 95%
50mA to 400mA Programmable Charge Current
±1% Feedback Voltage Accuracy
Programmable 5% Accurate Charge Current
Thermally Enhanced, Low Profile (0.75mm)
16-Lead (3mm × 3mm) QFN Package
APPLICATIONS
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Handheld Instruments
Solar Powered Devices
Industrial/Military Sensors and Devices
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
High Efficiency, Wide Input Voltage Range Charging with LTC4121
IN
10µF
10k
RUN
MPPT
INTV
CC
BOOST
2.2µF
22nF
SLF6025T-470MR48
EFFICIENCY (%)
95
LTC4121 Efficiency vs V
IN
at V
FLOAT
= 8.4V
97
200mA, R
PROG
= 6.04k
400mA, R
PROG
= 3.01k
LTC4121
SW
BAT
+
–
V
IN
V
BAT
+ 200mV
TO 40V
PROG
FREQ
CHGSNS
1.96M
FB
787k
GND FBG
93
22µF
91
+
Li-Ion
89
V
BAT
= 8.3V
5
10
15
20
25
V
IN
(V)
30
35
40
R
PROG
87
4121 TA01a
4121 TA01b
4121fc
For more information
www.linear.com/LTC4121
1
LTC4121/LTC4121-4.2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
IN, RUN,
CHRG, FAULT,
MPPT ................... –0.3V to 43V
BOOST ................................... V
SW
– 0.3V to (V
SW
+ 6V)
SW (DC) ........................................ –0.3V to (V
IN
+ 0.3V)
SW (Pulsed <100ns) ......................–1.5V to (V
IN
+ 1.5V)
CHGSNS, BAT, FB/BATSNS, FBG ................ –0.3V to 18V
FREQ, NTC, PROG, INTV
CC
.......................... –0.3V to 6V
I
CHGSNS
, I
BAT
..................................................... ±600mA
I
CHRG
, I
FAULT
, ........................................................±5mA
I
FB
, I
FBG
(LTC4121) .................................................±5mA
I
BATSNS
(LTC4121-4.2) ...........................................±5mA
I
INTVCC
.................................................................. –5mA
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Storage Temperature Range .................... –65°C to 150°
PIN CONFIGURATION
LTC4121
TOP VIEW
FAULT
CHRG
PROG
RUN
LTC4121-4.2
TOP VIEW
FAULT
CHRG
PROG
12 NTC
GND
11 NC
10 BATSNS
9
5
GND
6
MPPT
7
FREQ
8
CHGSNS
BAT
RUN
12 NTC
GND
11 FBG
10 FB
9
5
GND
6
MPPT
7
FREQ
8
CHGSNS
BAT
INTV
CC
1
BOOST 2
IN 3
SW 4
16 15 14 13
INTV
CC
1
BOOST 2
IN 3
SW 4
16 15 14 13
UD PACKAGE
16-LEAD (3mm
×
3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB TO OBTAIN
θ
JA
UD PACKAGE
16-LEAD (3mm
×
3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB TO OBTAIN
θ
JA
(http://www.linear.com/product/LTC4121#orderinfo)
LTC4121 Options
PART NUMBER
LTC4121
LTC4121-4.2
LEAD FREE FINISH
LTC4121EUD#PBF
LTC4121IUD#PBF
LTC4121EUD-4.2#PBF
LTC4121IUD-4.2#PBF
FLOAT VOLTAGE
Programmable
4.2V Fixed
TAPE AND REEL
LTC4121EUD#TRPBF
LTC4121IUD#TRPBF
LTC4121IUD-4.2#TRPBF
PART MARKING
LGHC
LGHC
LGMV
PACKAGE DESCRIPTION
16-Lead (3mm × 3mm) Plastic QFN
16-Lead (3mm × 3mm) Plastic QFN
16-Lead (3mm × 3mm) Plastic QFN
16-Lead (3mm × 3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
ORDER INFORMATION
LTC4121EUD-4.2#TRPBF LGMV
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
4121fc
For more information
www.linear.com/LTC4121
LTC4121/LTC4121-4.2
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
RUN
= 15V, V
CHGSNS
= V
BAT
= 4V, R
PROG
= 3.01k,
V
FB
= 2.29V (LTC4121), V
BATSNS
= 4V (LTC4121-4.2). Current into a pin is positive out of a pin is negative. (Note 2)
SYMBOL
PARAMETER
Operating Input Supply Range
Battery Voltage Range
I
IN
DC Supply Current
LTC4121 (Note 3)
LTC4121-4.2
Switching: FREQ = GND
Standby Mode: (Note 4)
Sleep Mode: (Note 4)
4.4V
6)
LTC4121-4.2: V
BATSNS
=
LTC4121: V
FB
= 2.51V (Note
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ELECTRICAL CHARACTERISTICS
CONDITIONS
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MIN
4.4
0
0
TYP
MAX
40
18
4.2
UNITS
V
V
V
mA
µA
µA
3.5
142
60
260
110
Disabled Mode: V
SD
< V
RUN
< V
EN
(Note 4)
Shutdown Mode: (Note 4)
∆V
DUVLO
Differential Undervoltage Lockout
Hysteresis
UV
INTVCC
INTV
CC
Undervoltage Lockout (Note 5)
Hysteresis
Battery Charger
I
BAT
BAT Standby Current
BAT Shutdown Current
I
BATSNS
I
FB
I
FBG_LEAK
R
FBG
V
FB(REG)
V
FLOAT
I
CHG
V
RCHG
V
RCHG_4.2
h
PROG
V
PROG
R
SNS
Ratio of BAT Current to PROG Current
PROG Pin Servo Voltage
CHGSNS-BAT Sense Resistor
I
BAT
= –100mA
BATSNS Standby Current (LTC4121-4.2)
Feedback Pin Bias Current (LTC4121)
Feedback Ground Leakage Current
(LTC4121)
Feedback Ground Return Resistance
(LTC4121)
Feedback Pin Regulation Voltage
(LTC4121)
Regulated Float Voltage (LTC4121-4.2)
(Note 6)
Standby Mode (LTC4121) (Notes 4, 8, 9)
Standby Mode (LTC4121-4.2) (Notes 4, 8, 9)
Shutdown Mode (LTC4121) (Notes 4, 8, 9)
Shutdown Mode (LTC4121-4.2) (Notes 4, 8, 9)
Standby Mode (Notes 4, 8, 9)
V
FB
= 2.5V (Note 6)
Shutdown Mode (Note 4)
V
IN
– V
BAT
Falling, V
IN
= 5V (LTC4121)
V
IN
– V
BATSNS
Falling, V
IN
= 5V (LTC4121-4.2)
V
IN
– V
BAT
Rising, V
IN
= 5V (LTC4121)
V
IN
– V
BATSNS
Rising, V
IN
= 5V (LTC4121-4.2)
INTV
CC
Rising, V
IN
= INTV
CC
+ 100mV
INTV
CC
Falling
37
20
20
80
115
80
40
160
µA
µA
mV
mV
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4.00
4.15
220
4.26
V
mV
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2.5
50
1100
10
5.4
1100
25
4.5
1000
2000
1000
10
2000
60
1
µA
nA
nA
nA
µA
nA
nA
µA
Ω
V
V
V
V
mA
mA
mV
mV
mA/mA
BATSNS Shutdown Current (LTC4121-4.2) Shutdown Mode (Notes 4, 8, 9)
1000
2.393
2.400
4.200
402
50
–49
–93
988
2000
2.407
2.418
4.212
4.231
421
55
–62
–114
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2.370
4.188
4.148
383
45
–38
–70
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Battery Charge Current
Battery Recharge Threshold
R
PROG
= 3.01k
R
PROG
= 24.3k
V
FB
Falling Relative to V
FB(REG)
(LTC4121)
V
BATSNS
Falling Relative to V
FLOAT
(LTC4121-4.2)
V
TRKL
< V
FB
< V
FB(REG)
(LTC4121),
V
TRKL_42
< V
BATSNS
< V
FLOAT
(LTC4121-4.2)
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1.206
1.227
300
1.248
V
mΩ
4121fc
For more information
www.linear.com/LTC4121
3
LTC4121/LTC4121-4.2
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
RUN
= 15V, V
CHGSNS
= V
BAT
= 4V, R
PROG
= 3.01k,
V
FB
= 2.29V (LTC4121), V
BATSNS
= 4V (LTC4121-4.2). Current into a pin is positive out of a pin is negative. (Note 2)
SYMBOL
I
LOWBAT
V
LOWBAT
PARAMETER
Low Battery Linear Charge Current
Low Battery Threshold Voltage
CONDITIONS
V
FB
< V
TRKL
, V
BAT
= 2.6V (LTC4121) (Note 6)
V
BATSNS
< V
TRKL_4.2
, V
BAT
= 2.6V (LTC4121-4.2)
V
BAT
Rising (LTC4121)
V
BATSNS
Rising (LTC4121-4.2)
Hysteresis
I
TRKL
Switch Mode Trickle Charge Current
PROG Pin Servo Voltage in Trickle Charge
V
TRKL
V
TRKL_4.2
h
C/10
Trickle Charge Threshold (LTC4121)
Hysteresis (LTC4121)
Trickle Charge Threshold (LTC4121-4.2)
Hysteresis (LTC4121-4.2)
End of Charge Indication Current Ratio
Safety Timer Termination Period
Bad Battery Termination Timeout
Switcher
f
OSC
t
MIN_ON
Switching Frequency
Minimum Controllable On-Time
Duty Cycle Maximum
Top Switch R
DSON
Bottom Switch R
DSON
I
PEAK
I
SW
Peak Inductor Current Limit
Switch Pin Current (Note 9)
I
SW
= –100mA
I
SW
= 100mA
Measured Across R
SNS
with a 15µH Inductor in
Series with R
SNS
(Note 10)
IN Open-Circuit, V
BAT
= V
SW
= 4.2V (LTC4121-4.2)
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IN Open-Circuit, V
BAT
= V
SW
= 8.4V (LTC4121)
Status Pins
FAULT, CHRG
Pin Output Voltage Low
Pin Leakage Current
NTC
Cold Temperature V
NTC
/V
INTVCC
Fault
Hot Temperature V
NTC
/V
INTVCC
Fault
NTC Disable Voltage
NTC Input Leakage Current
Rising V
NTC
Threshold
Falling V
NTC
Threshold
Falling V
NTC
Threshold
Rising V
NTC
Threshold
Falling V
NTC
Threshold
Rising V
NTC
Threshold
V
NTC
= V
INTVCC
–50
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ELECTRICAL CHARACTERISTICS
MIN
6
2.15
TYP
9
2.21
147
I
CHG
/10
122
MAX
16
2. 28
UNITS
mA
V
mV
mA
mV
V
LOWBAT
< V
BAT
, V
FB
< V
TRKL
(LTC4121) (Note 6)
V
LOWBAT
< V
BATSNS
< V
TRKL_42
(LTC4121-4.2)
V
LOWBAT
< V
BAT
, V
FB
> V
TRKL
(LTC4121) (Note 6)
V
LOWBAT
< V
BATSNS
< V
TRKL_42
(LTC4121-4.2)
V
FB
Rising (Note 6)
V
FB
Falling (Note 6)
V
BATSNS
Rising
V
BATSNS
Falling
(Note 7)
1.3
19
FREQ = INTV
CC
FREQ = GND
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1.65
2.86
1.68
50
2.91
88
0.1
2.0
30
1.5
0.75
120
1.71
2.98
V
mV
V
mV
mA/mA
2.8
42
2.0
1.0
hrs
min
MHz
MHz
ns
%
Ω
Ω
1.0
0.5
94
0.8
0.5
585
1050
7
15
1250
15
30
550
0
73
35.5
1
74
72
36.5
37.5
2
3
50
3
37.5
1
75
mA
µA
µA
mV
µA
%INTV
CC
%INTV
CC
%INTV
CC
%INTV
CC
%INTV
CC
%INTV
CC
nA
I = 2mA
V = 43V, Pin High-Impedance
4
4121fc
For more information
www.linear.com/LTC4121
LTC4121/LTC4121-4.2
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
RUN
= 15V, V
CHGSNS
= V
BAT
= 4V, R
PROG
= 3.01k,
V
FB
= 2.29V (LTC4121), V
BATSNS
= 4V (LTC4121-4.2). Current into a pin is positive out of a pin is negative. (Note 2)
SYMBOL
RUN
V
EN
Enable Threshold
Hysteresis
Run Pin Input Current
V
SD
FREQ
FREQ Pin Input Low
FREQ Pin Input High
FREQ Pin Input Current
MPPT
I
MPPT
T
MP
PW
MP
K
F
V
MP(OS)
MPPT Pin Leakage Current
MPPT Sample Period
MPPT Sample Pulse Width
Internal Divider Gain
MPPT Error Amp Gain Offset
V
MPPT
= 4.2V
Period Between Charger Disabled Events
Charger Disabled Pulse Width
Internal DAC Voltage as a Ratio to V
IN
V
MPPT
– V
DAC
, I
BAT
= 50%• I
CHG
0.098
10
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ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
V
RUN
Rising
V
RUN
Falling
V
RUN
= 40V
V
RUN
Falling
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MIN
2.35
TYP
2.45
200
0.01
MAX
2.55
0.1
1.2
UNITS
V
mV
µA
V
mV
V
Shutdown Threshold
Hysteresis
0.4
220
0.4
3.6
±1
15
28
36
0.1
–45
0.102
–100
1000
V
µA
nA
s
ms
V/V
mV
0 < V
FREQ
< V
INTVCC
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC4121 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC4121E is guaranteed to meet performance specifications
for junction temperatures from 0°C to 85°C. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC4121I is guaranteed over the full –40°C to 125°C operating
junction temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance, and other environmental factors.
Note 3:
If a battery voltage greater than 11V can be hot plugged to the
LTC4121 a reverse blocking diode is required in series with the BAT pin to
prevent large inrush current into the low impedance BAT pin.
Note 4:
Standby mode occurs when the LTC4121/LTC4121-4.2 stops
switching due to an NTC fault, MPPT pause, or when the charge current
has dropped low enough to enter Burst Mode operation. Disabled mode
occurs when V
RUN
is between V
SD
and V
EN
. Shutdown mode occurs
when V
RUN
is below V
SD
or when the differential undervoltage lockout
is engaged. Sleep mode occurs after a timeout while the battery voltage
remains above the V
RCHG
or V
RCHG_42
threshold.
Note 5:
The internal supply INTV
CC
should only be used for the NTC
divider, it should not be used for any other loads
Note 6:
For the LTC4121, the FB pin is measured with a resistance of 588k
in series with the pin.
Note 7:
h
C/10
is expressed as a fraction of measured full charge current as
measured at the PROG pin voltage when the
CHRG
pin de-asserts.
Note 8:
In an application circuit with an inductor connected from SW to
CHGSNS, the total battery leakage current when disabled is the sum of
I
BATSNS
and I
SW
(LTC4121-4.2) or I
BAT
and I
FBG_LEAK
and I
SW
(LTC4121).
Note 9:
When no supply is present at IN, the SW powers IN through the
body diode of the top side switch. This may cause additional SW pin
current depending on the load present at IN.
Note 10:
Guaranteed by design and/or correlation to static test.
4121fc
For more information
www.linear.com/LTC4121
5
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