LT3650-8.2/LT3650-8.4
High Voltage 2 Amp
Monolithic 2-Cell
Li-Ion Battery Charger
Description
Features
Wide Input Voltage Range: 9V to 32V (40V Absolute
Maximum)
n Programmable Charge Current: Up to 2A
n User-Selectable Termination: C/10 or Onboard
Termination Timer
n Dynamic Charge Rate Programming/Soft-Start Pin
n Programmable Input Current Limit
n 1MHz Fixed Frequency
n Average Current Mode Control
n 0.5% Float Voltage Accuracy
n 5% Charge Current Accuracy
n 2.5% C/10 Detection Accuracy
n NTC Resistor Temperature Monitor
n Auto-Recharge at 97.5% Float Voltage
n Auto-Precondition at 2V.
Typical Performance Characteristics
50
25
0
75
TEMPERATURE (°C)
UNITS
22.5
Timer Accuracy
–25
MAX
0.4
l
Precondition Timeout
–50
TYP
65
–50
–25
50
0
25
TEMPERATURE (°C)
75
100
365082 G02
0
0
0.2
0.4
0.8
0.6
VRNG/SS
1.0
1.2
365082 G03
36508284fd
4
LT3650-8.2/LT3650-8.4
Typical Performance Characteristics
Switch Drive (ISW/IBOOST)
vs Switch Current
Switch Forward Drop (VIN – VSW)
vs Temperature
36
480
33
SWITCH FORWARD DROP (mV)
27
21
18
15
12
9
6
440
0
400
380
VCLP – VIN (mV)
10
9
–25
50
25
0
75
TEMPERATURE (°C)
100
125
50
25
0
75
TEMPERATURE (°C)
–25
100
–350
125
100.8
50.6
100.6
50.4
100.4
50.2
50.0
49.8
49.6
100
60
40
20
25 35 45 55 65 75 85 95 105 115 125 135
TEMPERATURE (°C)
365082 G10
6
8
8.5
365082 G06
100
VBAT = 7.5V
99.6
99.2
99.0
–50
125
50
25
0
75
TEMPERATURE (°C)
–25
365082 G08
125
100
365082 G09
Battery Bias Current with Charger
Disabled (IBAT + ISENSE + IBOOST
+ ISW)
CC/CV Charging; BAT Pin Bias
Current vs VBAT
10
LT3650-8.2
9
8
IBAT (mA)
80
2 2.5 5.5
VSENSE (V)
99.8
99.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
–0.2
–0.4
1.5
100.0
49.2
50
25
0
75
TEMPERATURE (°C)
1
100.2
49.4
–25
0.5
IMAX Current Limit (VSENSE – VBAT)
vs Temperature
50.8
49.0
–50
0
365082 G05
101.0
365082 G07
120
VSENSE – VBAT (mV)
–300
51.0
Thermal Foldback – IMAX
Current Limit (VSENSE – VBAT)
vs Temperature
0
–150
CLP Input Limit Threshold
(VCLP – VIN) vs Temperature
ICHG at 50%
C/10 Threshold vs Temperature
(VSENSE – VBAT)
8
–50
–100
–250
320
–50
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCH CURRENT (A)
365082 G04
LT3650-8.2
–200
360
VSENSE – VBAT (mV)
0
CC/CV Charging; SENSE Pin Bias
Current vs VSENSE
–50
340
11
VSENSE – VBAT (mV)
50
420
3
12
460
BATTERY CURRENT (µA)
ISW/IBOOST
24
100
ISW = 2A
ISENSE (µA)
30
0
TA = 25°C, unless otherwise noted.
7
6
VIN FLOATING
5
4
3
2
1
0
0.5
1
1.5
2 2.5
VBAT (V)
3
3.5
8
8.5
365082 G11
0
VIN = 20V, VSHDN = 0V
0
1
2
3
4
5
VBAT (V)
6
7
8
9
365082 G12
36508284fd
5
LT3650-8.2/LT3650-8.4
Pin Functions
VIN (Pin 1): Charger Input Supply. VIN pin operating range
is 9V to 32V. VIN ≥ 11.5V or (VBOOST – VSW) > 2V is required for start-up. IVIN = 85µA after charge termination.
be pulled low. If no fault conditions exist, the FAULT pin
remains high impedance (see the Applications Information section).
CLP (Pin 2): System Current Limit Input. System current
levels can be monitored by connecting the input power
supply to the CLP pin and connecting a sense resistor
from the CLP pin to the VIN pin. Additional system load is
drawn from the VIN pin connection, and maximum system
load is achieved when VCLP – VVIN = 50mV. The LT3650
servos the maximum charge current required to maintain
programmed maximum system current. If this function is
not desired, connect the CLP pin to the VIN pin (see the
Applications Information section).
TIMER (Pin 6): End-Of-Cycle Timer Programming Pin.
If a timer-based charge termination is desired, connect
a capacitor from this pin to ground. Full charge end-ofcycle time (in hours) is programmed with this capacitor
following the equation:
SHDN (Pin 3): Precision Threshold Shutdown Pin. The
enable threshold is 1.225V (rising), with 120mV of input
hysteresis. When in shutdown mode, all charging functions
are disabled. The precision threshold allows use of the
SHDN pin to incorporate UVLO functions. If the SHDN pin
is pulled below 0.4V, the IC enters a low current shutdown
mode where the VIN pin current is reduced to 15µA. Typical SHDN pin input bias current is 10nA. If the shutdown
function is not desired, connect the pin to the VIN pin.
CHRG (Pin 4): Open-Collector Charger Status Output;
typically pulled up through a resistor to a reference voltage. This status pin can be pulled up to voltages as high
as VIN when disabled, and can sink currents up to 10mA
when enabled. During a battery charging cycle, CHRG is
pulled low. When the charge cycle is terminated, the CHRG
pin becomes high impedance. If the internal timer is used
for termination, the pin stays low during the charging
cycle until the charge current drops below a C/10 rate, or
ICHG(MAX)/10. A temperature fault also causes this pin to
be pulled low (see the Applications Information section).
FAULT (Pin 5): Open-Collector Fault Status Output; typically pulled up through a resistor to a reference voltage.
This status pin can be pulled up to voltages as high as VIN
when disabled, and can sink currents up to 10mA when
enabled. This pin indicates charge cycle fault conditions
during a battery charging cycle. A temperature fault causes
this pin to be pulled low. If the internal timer is used for
termination, a bad-battery fault also causes this pin to
tEOC = CTIMER • 4.4 • 106
A bad-battery fault is generated if the battery does not
reach the precondition threshold voltage within one-eighth
of tEOC, or:
tPRE = CTIMER • 5.5 • 105
A 0.68µF capacitor is typically used, which generates a
timer EOC at three hours, and a precondition limit time of
22.5 minutes. If a timer-based termination is not desired,
the timer function is disabled by connecting the TIMER
pin to ground. With the timer function disabled, charging
terminates when the charge current drops below a C/10
rate, or ICHG(MAX)/10.
RNG/SS (Pin 7): Charge Current Programming Pin. This
pin allows a dynamic adjustment of the maximum charge
current, and can be used to employ a soft-start function.
Maximum charge current is adjusted by setting the voltage on this pin, such that the maximum desired voltage
across the inductor current sense resistor (VSENSE – VBAT) is
0.1 • VRNG/SS, so the maximum charge current reduces to:
VRNG/SS • ICHG(MAX)
This pin has an effective range from 0V to 1V. 50µA is
sourced from this pin, so the maximum charge current
can be programmed by connecting a resistor (RRNG/SS)
from RNG/SS to ground, such that the voltage dropped
across the resistor is equivalent to the desired programming voltage, or:
VRNG/SS = 50µA • RRNG/SS
Soft-start functionality can be implemented by connecting a capacitor (CRNG/SS) from RNG/SS to ground, such
that the time required to charge the capacitor to 1V (full
36508284fd
6
LT3650-8.2/LT3650-8.4
Pin Functions
charge current) is the desired soft-start interval (tSS).
For no RRNG/SS, this capacitor value follows the relation:
CRNG/SS = 50µA • tSS
The RNG/SS pin is pulled low during fault conditions,
allowing graceful recovery from faults should soft-start
functionality be implemented. Both the soft-start capacitor and the programming resistor can be implemented in
parallel. All C/10 monitoring functions are disabled while
VRNG/SS is below 0.1V to accommodate long soft-start
intervals.
RNG/SS voltage can also be manipulated using an active
device, employing a pull-down transistor to disable charge
current or to dynamically servo maximum charge current.
Manipulation of the RNG/SS pin with active devices that
have low impedance pull-up capability is not allowed (see
the Applications Information section).
NTC (Pin 8): Battery Temperature Monitor Pin. This pin is
the input to the NTC (Negative Temperature Coefficient)
thermistor temperature monitoring circuit. This function is
enabled by connecting a 10kΩ, B = 3380 NTC thermistor
from the NTC pin to ground. The pin sources 50µA, and
monitors the voltage across the 10kΩ thermistor. When
the voltage on this pin is above 1.36V (T < 0°C) or below
0.29V (T > 40°C), charging is disabled and the CHRG and
FAULT pins are both pulled low. If internal timer termination is being used, the timer is paused, suspending the
charging cycle. Charging resumes when the voltage on
NTC returns to within the 0.29V to 1.36V active region.
There is approximately 5°C of temperature hysteresis
associated with each of the temperature thresholds. The
temperature monitoring function remains enabled while
thermistor resistance to ground is less than 250kΩ, so if
this function is not desired, leave the NTC pin unconnected.
BAT (Pin 9): Battery Voltage Monitor Pin. Connect 10µF
decoupling capacitance (CBAT) from this pin to ground.
Depending on application requirements, larger value decoupling capacitors may be required (see the Application
Information section). The charge function operates to
achieve the final float voltage at this pin. The auto-restart
feature initiates a new charging cycle when the voltage at
the BAT pin falls 2.5% below this float voltage. Once the
charge cycle is terminated, the input bias current of the BAT
pin is reduced to 2V.
1
2
V V
ICVIN(RMS) ICHG(MAX) • BAT • IN − 1
VIN VBAT
which has a maximum at VIN = 2 • VBAT, where:
ICVIN(RMS) = ICHG(MAX)/2
The simple worst-case of 1/2 • ICHG(MAX) is commonly
used for design.
Bulk capacitance is a function of desired input ripple voltage (∆VIN), and follows the relation:
V /V
CIN(BULK) = IMAX • BAT IN (µF )
∆VIN
10µF is typically adequate for most charger applications.
BOOST Supply
The BOOST bootstrapped supply rail drives the internal
switch and facilitates saturation of switch transistor. Operating range of the BOOST pin is 0V to 8.5V, as referenced
to the SW pin. Connect a 1µF or greater capacitor from
the BOOST pin to the SW pin.
The voltage on the decoupling capacitor is refreshed
through a diode, with the anode connected to/from either
the battery output voltage or an external source, and the
cathode connected to the BOOST pin. Rate the diode average current greater than 0.1A, and its reverse voltages
greater than VIN(MAX).
When an LT3650 charger is not switching, the SW pin is at
the same potential as the battery, which can be as high as
VBAT(FLT). For reliable start-up, the VIN supply must be at
least 3V above the SW pin. The minimum start-up specification of VIN at or above 11.5V provides ample margin
to satisfy this requirement. Once switching begins, the
BOOST supply capacitor gets charged such that (VBOOST
– VSW) > 2V, and the VIN requirement no longer applies.
In low VIN applications, the BOOST supply can be powered
by an external source for start-up, eliminating the VIN
start-up requirement.
VBAT Output Decoupling
An LT3650 charger output requires bypass capacitance
connected from the BAT pin to ground (CBAT). A 10µF ceramic capacitor is required for all applications. In systems
where the battery can be disconnected from the charger
output, additional bypass capacitance may be desired for
visual indication of a no-battery condition (see the Status
Pins section).
If it is desired to operate a system load from the LT3650
charger output when the battery is disconnected, additional
bypass capacitance is required. In this type of application
with the charger being used as a DC/DC converter, excessive ripple and/or low amplitude oscillations can occur
without additional output bulk capacitance. For these applications, place a 100µF low ESR nonceramic capacitor
(chip tantalum or organic semiconductor capacitors such
as Sanyo OS-CONs or POSCAPs) from BAT to ground,
in parallel with the 10µF ceramic bypass capacitor. This
additional bypass capacitance may also be required in
systems where the battery is connected to the charger
through long wires. The voltage rating on CBAT must meet
or exceed the battery float voltage.
36508284fd
11
LT3650-8.2/LT3650-8.4
Applications Information
RSENSE : Charge Current Programming
The LT3650 charger is configurable to charge at average
currents as high as 2A. Maximum charge current is set by
choosing an inductor sense resistor such that the desired
maximum average current through that sense resistor
creates a 100mV drop, or:
0.1
RSENSE =
IMAX(AVG)
where IMAX(AVG) is the maximum average charge current.
A 2A charger, for example, would use a 0.05Ω sense
resistor.
to 35% of IMAX, so an inductor value can be determined
by setting 0.25 < ∆IMAX < 0.35.
Magnetics vendors typically specify inductors with
maximum RMS and saturation current ratings. Select an
inductor that has a saturation current rating at or above
(1+∆IMAX/2) • IMAX, and an RMS rating above IMAX. Inductors must also meet a maximum volt-second product
requirement. If this specification is not in the data sheet of
an inductor, consult the vendor to make sure the maximum
volt-second product is not being exceeded by your design.
The minimum required volt-second product is:
VBAT
VBAT • 1 −
(V • µs)
VIN(MAX)
SW
BOOST
LT3650
SENSE
RSENSE
BAT
365082 F01
Figure 1. Programming Maximum Charge Current Using RSENSE
SWITCHED INDUCTOR VALUE (µH)
14
Inductor Selection
10
L=
• RSENSE • (VBAT + VF )
∆IMAX
V + V
• 1− BAT F (µH)
+V
V
IN(MAX) F
In the previous relation, ∆IMAX is the normalized ripple
current, VIN(MAX) as the maximum operational voltage,
and VF is the forward voltage of the rectifying Schottky
diode. Ripple current is typically set within a range of 25%
12
10
8
6
4
2
0
9
12 15 18 21 24 27 30 32
MAXIMUM OPERATIONAL VIN VOLTAGE (V)
365082 F02
Figure 2. 2A Charger Switched Inductor Value
(RSENSE = 0.05Ω) 25% to 35% IMAX Ripple Current
20
SWITCHED INDUCTOR VALUE (µH)
The primary criteria for inductor value selection in an
LT3650 charger is the ripple current created in that inductor.
Once the inductance value is determined, an inductor must
also have a saturation current equal to or exceeding the
maximum peak current in the inductor. An inductor value
(L), given the desired amount of ripple current (∆IMAX)
can be approximated using the relation:
12
18
16
14
12
10
8
6
4
2
0
9
12 15 18 21 24 27 30 32
MAXIMUM OPERATIONAL VIN VOLTAGE (V)
365082 F03
Figure 3. 1.3A Charger Switched Inductor Value
(RSENSE = 0.075Ω) 25% to 35% IMAX Ripple Current
36508284fd
LT3650-8.2/LT3650-8.4
Applications Information
Rectifier Selection
CLP: System Current Limit
The rectifier diode in an LT3650 battery charger provides a
current path for the inductor current when the main power
switch is disabled. The rectifier is selected based upon
forward voltage, reverse voltage, and maximum current.
A Schottky diode is required, as low forward voltage yields
the lowest power loss and highest efficiency. The rectifier
diode must be rated to withstand reverse voltages greater
than the maximum VIN voltage.
The LT3650 contains a PowerPathTM control feature to
support multiple load systems. The charger adjusts output current in response to a system load if overall input
supply current exceeds the programmed maximum value.
The minimum average diode current rating (IDIODE(MAX)) is
calculated with maximum output current (IMAX), maximum
operational VIN, and output at the precondition threshold
(VBAT(PRE)):
IMAX • (VIN(MAX) − VBAT(PRE) )
IDIODE(MAX) >
(A)
VIN(MAX)
For example, a rectifier diode for an 8.2V, 1.5A charger
with a 20V maximum input voltage would require:
Maximum input supply current is set by choosing a sense
resistor (RCLP) such that the desired maximum current
through that sense resistor creates a 50mV drop, or:
0.05
RCLP =
IMAX(IN)
where IMAX(IN) is the maximum input current. A 1.5A system limit, for example, would use a 33mΩ sense resistor.
The LT3650 integrates the CLP signal internally, so average current limiting is performed in most cases without
the need for external filter elements.
1.5 • (20 − 5.65)
,or
20
IDIODE(MAX) > 1.1A
IDIODE(MAX) >
SYSTEM LOAD
CURRENT
1.5A
SYSTEM LOAD
INPUT SUPPLY
RCLP
1.0A
VIN
LT3650 INPUT
CURRENT (IVIN)
LT3650
0.5A
CLP
365082 F04
Figure 4. RCLP Sets the Input Supply Current Limit
365082 F05
Figure 5. CLP Limit: Charger Current vs
System Load Current with 1.5A Limit
36508284fd
13
LT3650-8.2/LT3650-8.4
Applications Information
RNG/SS: Dynamic Charge Current Adjust
The LT3650 gives the user the capability to adjust maximum
charge current dynamically through the RNG/SS pin. The
voltage on the RNG/SS pin corresponds to ten times the
maximum voltage across the sense resistor (RSENSE). The
default maximum sense voltage is 100mV, so maximum
charge current can be expressed as:
This feature could be used, for example, to switch in a
reduced charge current level. Active servos can also be
used to impose voltages on the RNG/SS pin, provided they
can only sink current. Active circuits that source current
cannot be used to drive the RNG/SS pin. Resistive pullups can be used, but extreme care must be taken not to
exceed the 2.5V absolute maximum voltage on the pin.
IMAX(RNG/SS) = IMAX • VRNG/SS
RNG/SS: Soft-Start
where IMAX(RNG/SS) is the maximum charge current if
VRNG/SS is within 0V to 1V. Voltages higher than 1V have
no effect on the maximum charge current.
Soft-start functionality is also supported by the RNG/SS
pin. 50µA is sourced from the RNG/SS pin, so connecting
a capacitor from the RNG/SS pin to ground (CRNG/SS) creates a linear voltage ramp. The maximum charge current
follows this voltage. Thus, the charge current increases
from zero to the fully programmed value as the capacitor
charges from 0V to 1V. The value of CRNG/SS is calculated
based on the desired time to full current (tSS) following
the relation:
The LT3650 sources 50µA from the RNG/SS pin, such that
a current control voltage can be set by simply connecting
an appropriately valued resistor to ground, following the
relation:
V
RRNG/SS = RNG/SS
50µA
For example, to reduce the maximum charge current to 50%
of the original value, which corresponds to a maximum
sense voltage of 50mV, RNG/SS would be set to 0.5V.
0.5V
RRNG/SS =
= 10kΩ
50µA
CRNG/SS = 50µA • tSS
The RNG/SS pin is pulled to ground internally when charging is terminated so each new charging cycle begins with
a soft-start cycle. RNG/SS is also pulled to ground during
bad-battery and NTC fault conditions, so a graceful recovery
from these faults is possible.
LT3650
LT3650
RNG/SS
RNG/SS
10k
365082 F06
365082 F07
LOGIC HIGH = HALF CURRENT
Figure 6. Using the RNG/SS Pin for Digital
Control of Maximum Charge Current
+
–
SERVO REFERENCE
Figure 7. Driving the RNG/SS Pin with a
Current-Sink Active Servo Amplifier
LT3650
RNG/SS
CPROG
365082 F08
Figure 8. Using the RNG/SS Pin for Soft-Start
36508284fd
14
LT3650-8.2/LT3650-8.4
Applications Information
Status Pins
The LT3650 reports charger status through two opencollector outputs, the CHRG and FAULT pins. These pins
can accept voltages as high as VIN, and can sink up to
10mA when enabled.
The CHRG pin indicates that the charger is delivering current at greater than a C/10 rate, or one-tenth of the programmed maximum charge current. The FAULT pin signals
bad-battery and NTC faults. These pins are binary coded,
and signal following the table below, where On indicates
the pin pulled low, and Off indicates pin high impedance:
voltage is achieved, the charge current falls until the C/10
threshold is reached, at which time the charger terminates
and the LT3650 enters standby mode. The CHRG status
pin follows the charger cycle and is high impedance when
the charger is not actively charging.
When VBAT drops below 97.5% of the full-charged float
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging.
There is no provision for bad-battery detection if C/10
termination is used.
Timer Termination
Table 1. Status Pins State Table
STATUS PINS STATE
CHRG
FAULT
CHARGER STATUS
Off
Off
Not Charging—Standby or Shutdown Mode
Off
On
Bad-Battery Fault
(Precondition Timeout/EOC Failure)
On
Off
Normal Charging at C/10 or Greater
On
On
NTC Fault (Pause)
If the battery is removed from an LT3650 charger that is
configured for C/10 termination, a sawtooth waveform
of approximately 100mV appears at the charger output,
due to cycling between termination and recharge events.
This cycling results in pulsing at the CHRG output. An
LED connected to this pin will exhibit a blinking pattern,
indicating to the user that a battery is not present. The
frequency of this blinking pattern is dependent on the
output capacitance.
C/10 Termination
The LT3650 supports a low current based termination
scheme, where a battery charge cycle terminates when
the current output from the charger falls to below onetenth the maximum current, as programmed with RSENSE.
The C/10 threshold current corresponds to 10mV across
RSENSE. This termination mode is engaged by shorting
the TIMER pin to ground.
When C/10 termination is used, an LT3650 charger sources
battery charge current as long as the average current level
remains above the C/10 threshold. As the full-charge float
The LT3650 supports a timer-based termination scheme, in
which a battery charge cycle is terminated after a specific
amount of time elapses. Timer termination is engaged
when a capacitor (CTIMER) is connected from the TIMER
pin to ground. The timer cycle EOC (tEOC) occurs based
on CTIMER following the relation:
CTIMER = tEOC • 2.27 • 10–7 (Hours)
Timer EOC is typically set to three hours, which requires
a 0.68µF capacitor.
The CHRG status pin continues to signal charging at a C/10
rate, regardless of which termination scheme is used. When
timer termination is used, the CHRG status pin is pulled
low during a charging cycle until the charger output current falls below the C/10 threshold. The charger continues
to top off the battery until timer EOC, when the LT3650
terminates the charging cycle and enters standby mode.
Termination at the end of the timer cycle only occurs if
the charging cycle was successful. A successful charge
cycle occurs when the battery is charged to within 2.5%
of the full-charge float voltage. If a charge cycle is not
successful at EOC, the timer cycle resets and charging
continues for another full timer cycle.
When VBAT drops below 97.5% of the full-charge float
voltage, whether by battery loading or replacement of
the battery, the charger automatically re-engages and
starts charging.
36508284fd
15
LT3650-8.2/LT3650-8.4
Applications Information
Preconditioning and Bad-Battery Fault
Battery Temperature Fault: NTC
An LT3650 charger has a precondition mode, in which
charge current is limited to 15% of the programmed IMAX,
as set by RSENSE. The precondition current corresponds
to 15mV across RSENSE.
The LT3650 can accommodate battery temperature monitoring by using an NTC (negative temperature coefficient)
thermistor close to the battery pack. The temperature
monitoring function is enabled by connecting a 10kΩ
B = 3380 NTC thermistor from the NTC pin to ground. If
the NTC function is not desired, leave the pin unconnected.
Precondition mode is engaged while the voltage on the BAT
pin is below the precondition threshold (VBAT(PRE)). Once
the BAT voltage rises above the precondition threshold,
normal full-current charging can commence. The LT3650
incorporates 1.5% of threshold hysteresis to prevent
mode glitching.
When the internal timer is used for termination, badbattery detection is engaged. This fault detection feature
is designed to identify failed cells. A bad-battery fault is
triggered when the voltage on BAT remains below the
precondition threshold for greater than one-eighth of a
full timer cycle (one-eighth EOC). A bad-battery fault is
also triggered if a normally charging battery re-enters
precondition mode after one-eighth EOC.
When a bad-battery fault is triggered, the charging cycle
is suspended, so the CHRG status pin becomes high
impedance. The FAULT pin is pulled low to signal a fault
detection. The RNG/SS pin is also pulled low during this
fault, to accommodate a graceful restart, in the event that
a soft-start function is incorporated (see the RNG/SS:
Soft-Start section).
Cycling the charger’s power or SHDN function initiates
a new charging cycle, but an LT3650 charger does not
require a reset. Once a bad-battery fault is detected, a new
timer charging cycle initiates when the BAT pin exceeds
the precondition threshold voltage. During a bad-battery
fault, 0.5mA is sourced from the charger; removing the
failed battery allows the charger output voltage to rise and
initiate a charge cycle reset. As such, removing a bad battery resets the LT3650, so a new charge cycle is started
by connecting another battery to the charger output.
The NTC pin sources 50µA, and monitors the voltage
dropped across the 10kΩ thermistor. When the voltage
on this pin is above 1.36V (0°C) or below 0.29V (40°C),
the battery temperature is out of range, and the LT3650
triggers an NTC fault. The NTC fault condition remains until
the voltage on the NTC pin corresponds to a temperature
within the 0°C to 40°C range. Both hot and cold thresholds
incorporate hysteresis that corresponds to 5°C.
If higher operational charging temperatures are desired,
the temperature range can be expanded by adding series resistance to the 10k NTC resistor. Adding a 0.91k
resistor will increase the effective temperature threshold
to 45°C.
During an NTC fault, charging is halted and both status
pins are pulled low. If timer termination is enabled, the
timer count is suspended and held until the fault condition is relieved. The RNG/SS pin is also pulled low during
this fault, to accommodate a graceful restart in the event
that a soft-start function is being incorporated (see the
RNG/SS: Soft-Start section).
Thermal Foldback
The LT3650 contains a thermal foldback protection feature
that reduces maximum charger output current if the IC
junction temperature approaches 125°C. In most cases,
on-chip temperatures servo such that any overtemperature conditions are relieved with only slight reductions in
maximum charger current.
In some cases, the thermal foldback protection feature
can reduce charger currents below the C/10 threshold. In
applications that use C/10 termination (TIMER = 0V), the
LT3650 will suspend charging and enter standby mode
until the overtemperature condition is relieved.
36508284fd
16
LT3650-8.2/LT3650-8.4
Applications Information
Layout Considerations
The LT3650 switch node has rise and fall times that are
typically less than 10ns to maximize conversion efficiency.
The switched node (Pin SW) trace should be kept as short
as possible to minimize high frequency noise. The input
capacitor (CIN) should be placed close to the IC to minimize
this switching noise. Short, wide traces on these nodes
also help to avoid voltage stress from inductive ringing.
The BOOST decoupling capacitor should also be in close
proximity to the IC to minimize inductive ringing. The
SENSE and BAT traces should be routed together and
kept as short as possible. Shielding these signals from
switching noise with ground is recommended.
High current paths and transients should be kept isolated from battery ground, to assure an accurate output
voltage reference. Effective grounding can be achieved
by considering switched current in the ground plane,
and careful component placement and orientation can
CIN
effectively steer these high currents such that the battery
reference does not get corrupted. Figure 9 illustrates an
effective grounding scheme using component placement
to control ground currents. When the switch is enabled
(loop #1), current flows from the input bypass capacitor
(CIN) through the switch and inductor to the battery positive terminal. When the switch is disabled (loop #2), the
current to the battery positive terminal is provided from
ground through the freewheeling Schottky diode (DF). In
both cases, these switched currents return to ground via
the output bypass capacitor (CBAT).
The LT3650 packaging has been designed to efficiently
remove heat from the IC via the exposed pad on the
backside of the package, which is soldered to a copper
footprint on the PCB. This footprint should be made as
large as possible to reduce the thermal resistance of the
IC case to ambient air.
CBAT
VBAT
RSENSE
1
2
DF
+
LT3650
VIN
SW
SENSE
BAT
365082 F09
Figure 9. Component Orientation Isolates High Current Paths From Sensitive Nodes
36508284fd
17
LT3650-8.2/LT3650-8.4
Typical Applications
12V to 32V 2A Charger with C/10 Termination.
A Dual LT6004 Provides Thermal Foldback, Reducing Maximum Charge Current for Temperatures Higher Than 35°C
D4
B340A
VIN
12V TO
32V
B340A
VIN
SW
CLP
BOOST
1µF
10µF
LT3650
D2
SHDN
D5
5.1k
0.05Ω
SENSE
BAT
CHRG
5.1k
L1
10µH
CMPSH1-4
10µF
FAULT
NTC
RNG/SS
TIMER
182k (3)
LT6004
CMHZ4684LTM
2.0
1.5
–INA
OUTB
+INA
–INB
V–
+INB
470k
CMHZ4684LTM
274k
1.0
4.99k
0.5
0
V+
OUTA
10nF
(2)
3.3nF
MAXIMUM CHARGE CURRENT (A)
(1)
Si1032R
2.5
25
30
35
40
TEMPERATURE (°C)
45
274k
50
365082 TA02
12V to 32V 2A Charger with Three Hour EOC Termination and
Removable Battery Pack. The RNG/SS Pin Is Used to Reduce the
Maximum Charge Current if 12V < VIN < 20V; Input UVLO = 10V.
NTC Range Is Extended to +45C. The Charger Can Supply Loads Up
to the Maximum Charge Current with No Battery Connected
CMSH3-40MA
RNG/SS Pin Foldback:
ICHG(MAX) vs VIN
CMSH3-40MA
SW
VIN
10µF
MM5Z9V1ST1
(9.1V)
1µF
BOOST
CLP
LT3650
SHDN
10µH
CMPSH1-4
SENSE
0.05Ω
CHRG
36k
BAT
10µF
FAULT
RNG/SS
3k
0.1µF
NTC
+
100µF
SYSTEM
LOAD
0.91k
TIMER
0.68µF
B = 3380
10k
+
365082 TA03a
18
MAXIMUM CHARGE CURRENT (A)
VIN
12V TO
32V
+
B = 3800
10k
365082 TA02b
2.0
1.5
1.0
0.5
0
10
12
14
18
16
VIN
20
22
32
365082 TA03b
36508284fd
LT3650-8.2/LT3650-8.4
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DD Package
12-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
0.70 ±0.05
3.50 ±0.05
2.10 ±0.05
2.38 ±0.05
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.45 BSC
2.25 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
3.00 ±0.10
(4 SIDES)
R = 0.115
TYP
7
0.40 ±0.10
12
2.38 ±0.10
1.65 ±0.10
PIN 1 NOTCH
R = 0.20 OR
0.25 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
6
0.200 REF
1
0.23 ±0.05
0.45 BSC
0.75 ±0.05
2.25 REF
0.00 – 0.05
(DD12) DFN 0106 REV A
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
36508284fd
19
LT3650-8.2/LT3650-8.4
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSE Package
12-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1666 Rev F)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
5.23
(.206)
MIN
2.845 ±0.102
(.112 ±.004)
0.889 ±0.127
(.035 ±.005)
6
1
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102 3.20 – 3.45
(.065 ±.004) (.126 – .136)
12
0.65
0.42 ±0.038
(.0256)
(.0165 ±.0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
7
NO MEASUREMENT PURPOSE
0.406 ±0.076
(.016 ±.003)
REF
12 11 10 9 8 7
DETAIL “A”
0° – 6° TYP
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
1 2 3 4 5 6
0.650
(.0256)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MSE12) 0911 REV F
36508284fd
20
LT3650-8.2/LT3650-8.4
Revision History
(Revision history begins at Rev D)
REV
DATE
DESCRIPTION
D
12/12
Added new Battery Bias Current curve
PAGE NUMBER
5
36508284fd
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.
21
LT3650-8.2/LT3650-8.4
Typical Application
12V to 32V 1.5A PowerPath Charger with C/10 Termination and 1A Input Supply Limit.
Status Pins Use LED Indicators
INPUT SUPPLY
12V TO 32V
1A
B240A
SYSTEM
LOAD
0.05Ω
B240A
VIN
SW
CLP
BOOST
B240A
1µF
402k
LT3650
47k
10k
10k
10µF
15µH
BAS40
SHDN
SENSE
CHRG
BAT
FAULT
NTC
TIMER
RNG/SS
0.068Ω
10µF
365082 TA04
+
0.1µF
B = 3380
10k
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
LT1511
3A Constant-Current/Constant-Voltage
Battery Charger
High Efficiency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd
Batteries, 24-Lead SO Package
LT1513
SEPIC Constant or Programmable Current/
Constant-Voltage Battery Charger
Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage, 500kHz
Switching Frequency, DD-Pak and TO-220 Packages
LT1571
1.5A Switching Charger
1- or 2-Cell Li-Ion, 500kHz or 200kHz Switching Frequency, Termination Flag, 16- and
28-Lead SSOP Packages
LTC1729
Li-Ion Battery Charger Termination
Controller
Trickle Charge Preconditioning, Temperature Charge Qualification, Time or Charge Current
Termination, Automatic Charger and Battery Detection, and Status Output, MS8 and
SO-8 Packages
LT1769
2A Switching Charger
Constant-Current/Constant-Voltage Switching Regulator, Input Current Limiting
Maximizes Charge Current, 20-Lead TSSOP and 28-Lead SSOP Packages
LT3650-4.1/
LT3650-4.2
High Voltage 2-Amp Monolithic 1-Cell
Li-Ion Battery Charger
VIN: 4.75 to 32V (40V Absolute Maximum), FSW: 1MHz, User-Selectable C/10 or
Programmable Termination Timer, 3mm × 3mm DFN-12 Package
LTC4002
Standalone Li-Ion Switch Mode
Battery Charger
Complete Charger for 1- or 2-Cell Li-Ion Batteries, Onboard Timer Termination,
Up to 4A Charge Current, 10-Lead DFN and SO-8 Packages
LTC4006
Small, High Efficiency, Fixed Voltage Li-Ion
Battery Charger with Termination
Complete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit and
Thermistor Sensor, 16-Lead Narrow SSOP Package
LTC4007
High Efficiency, Programmable Voltage
Battery Charger with Termination
Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor
Sensor and Indicator Outputs, 24-Lead SSOP Package
LTC4008
4A, High Efficiency, Multi-Chemistry
Battery Charger
Complete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries,
Up to 96% Efficiency, 20-Lead SSOP Package
LTC4009/
LTC4009-1/
LTC4009-2
4A, High Efficiency, Multi-Chemistry
Battery Charger
Constant-Current/Constant-Voltage Switching Regulator Charger, Resistor Voltage/
Current Programming, AC Adapter Current Limit and Thermistor Sensor and Indicator
Outputs 1- to 4-Cell Li, Up to 18-Cell Ni, SLA and Supercap Compatible; 4mm × 4mm
QFN-20 Package, LTC4009-1 Version for 4.1V Float Voltage Li-Ion, LTC4009-2 Version for
4.2V Float Voltage Li-Ion Cells.
36508284fd
22 Linear Technology Corporation
LT 1212 REV D • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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