LINER LTC4078XEDD

LTC4078X
Dual Input Li-Ion Battery
Charger with Overvoltage Protection
FEATURES
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22V Maximum Voltage for Wall Adapter and
USB Inputs
Charge Single-Cell Li-Ion Batteries from Wall
Adapter and USB Inputs
Automatic Input Power Detection and Selection
Charge Current Programmable Up to 950mA from
Wall Adapter Input
Overvoltage Lockout for Wall Adapter and USB Inputs
Battery Detection Input Disables Charger When No
Battery is Present
No External MOSFET, Sense Resistor or Blocking
Diode Needed
Thermal Regulation Maximizes Charge Rate Without
Risk of Overheating*
Preset Charge Voltage with ±0.6% Accuracy
Programmable Charge Current Termination
40µA USB Suspend Current in Shutdown
Charge Status Output
Automatic Recharge
No Trickle Charge
Available in a Thermally Enhanced, Low Profile
(0.75mm) 10-Lead (3mm × 3mm) DFN Package
APPLICATIONS
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The LTC®4078X is a standalone linear charger that is
capable of charging a single-cell Li-Ion/Polymer battery
from both wall adapter and USB inputs. The charger can
detect power at the inputs and automatically select the
appropriate power source for charging.
No external sense resistor or blocking diode is required
for charging due to the internal MOSFET architecture.
The LTC4078X features a maximum 22V rating for both
wall adapter and USB inputs, although charging stops if
the selected power source exceeds the overvoltage limit.
Internal thermal feedback regulates the battery charge
current to maintain a constant die temperature during high
power operation or high ambient temperature conditions.
The float voltage is fixed at 4.2V and the charge current
is programmed with an external resistor. The LTC4078X
terminates the charge cycle when the charge current drops
below the programmed termination threshold after the
final float voltage is reached.
Other features include battery present detection, automatic
recharge, undervoltage lockout, charge status outputs, and
“power present” status outputs to indicate the presence of
wall adapter or USB power. The device is offered in a low
profile (0.75mm) 3mm × 3mm 10-lead DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All
other trademarks are the property of their respective owners.
*Protected by U.S. Patents including 6522118, 6700364.
Cellular Telephones
Handheld Computers
Portable MP3 Players
Digital Cameras
TYPICAL APPLICATION
Charger Current vs Supply Voltage
900
High Voltage Dual Input Battery Charger
for Li-Ion Battery Pack
USB
PORT
1µF
800mA (WALL)
500mA (USB)
LTC4078X
WALL
ADAPTER
BAT
DCIN
USBIN
1µF
BATDET
3.9k
IUSB
2k
IDC
1% 1.24k
1%
ITERM
GND
+
700
RIDC = 1.24k
RIUSB = 2k
VBAT = 3.5V
VBATDET = 0V
600
CHARGE FROM DCIN
800
4.2V
Li-Ion
BATTERY
PACK
2k
1%
IBAT (mA)
■
DESCRIPTION
500
400
CHARGE
FROM USBIN
300
200
100
0
4078X TA01
2
3
4
5
6
7
8
SUPPLY VOLTAGE (V)
19
20
4078x TA01b
4078xf
1
LTC4078X
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Input Supply Voltage (DCIN, USBIN) ............–0.3 to 22V
ENABLE, ⎯C⎯H⎯R⎯G, ⎯P⎯W⎯R, BATDET, BAT...............–0.3 to 6V
IDC, IUSB, ITERM Pin Current .................................1mA
DCIN, USBIN, BAT Pin Current ....................................1A
BAT Short-Circuit Duration............................Continuous
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
TOP VIEW
10 DCIN
USBIN
1
IUSB
2
ITERM
3
PWR
4
7 BATDET
CHRG
5
6 ENABLE
9 BAT
11
8 IDC
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 40°C/W (Note 3)
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4078XEDD#PBF
LTC4078XEDD#TRPBF
LCYP
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDCIN = 5V, VUSBIN = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
VDCIN
Operating Supply Voltage
VUSBIN
Operating Supply Voltage
5.5
V
IDCIN
DCIN Supply Current
Charge Mode (Note 4), RIDC = 10k
Standby Mode; Charge Terminated
Shutdown Mode (ENABLE = 5V)
Overvoltage Mode (VDCIN = 10V)
●
●
350
70
40
70
800
120
80
140
µA
µA
µA
µA
IUSBIN
USBIN Supply Current
Charge Mode (Note 5), RIUSB = 10k, VDCIN = 0V
Standby Mode; Charge Terminated, VDCIN = 0V
Shutdown (VDCIN = 0V, ENABLE = 0V)
Overvoltage Mode (VUSBIN = 10V)
VDCIN > VUSBIN
●
●
350
70
40
70
23
800
120
80
140
40
µA
µA
µA
µA
µA
VFLOAT
Regulated Output (Float) Voltage
IBAT = 1mA
IBAT = 1mA, 0°C < TA < 85°C
4.185
4.165
4.2
4.2
4.215
4.235
V
V
IBAT
BAT Pin Current
RIDC = 1.25k, Constant-Current Mode
RIUSB = 2.1k, Constant-Current Mode
RIDC = 10k or RIUSB = 10k
Standby Mode, Charge Terminated
Shutdown Mode (Charger Disabled)
Sleep Mode (VDCIN = 0V, VUSBIN = 0V)
770
455
93
800
476
100
–7.5
–7.5
–7.5
830
495
107
–12
–12
–12
●
4.3
●
4.3
●
●
●
TYP
MAX
5.5
UNITS
V
mA
mA
mA
µA
µA
µA
4078xf
2
LTC4078X
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDCIN = 5V, VUSBIN = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VIDC
IDC Pin Regulated Voltage
Constant-Current Mode
1
V
VIUSB
IUSB Pin Regulated Voltage
Constant-Current Mode
1
V
ITERMINATE
Charge Current Termination Threshold
RITERM = 1k
RITERM = 2k
RITERM = 10k
RITERM = 20k
VUVDC
DCIN Undervoltage Lockout Voltage
VUVUSB
●
●
●
●
90
42
8
3.5
100
50
10
5
110
58
12
6.5
mA
mA
mA
mA
From Low to High
Hysteresis
4
4.15
190
4.3
V
mV
USBIN Undervoltage Lockout Voltage
From Low to High
Hysteresis
3.8
3.95
170
4.1
V
mV
VOVDC
DCIN Overvoltage Lockout Voltage
From Low to High
Hysteresis
5.8
6
185
6.2
V
mV
VOVUSB
USBIN Overvoltage Lockout Voltage
From Low to High
Hysteresis
5.8
6
185
6.2
V
mV
VASD-DC
VDCIN – VBAT Lockout Threshold
VDCIN from Low to High, VBAT = 4.2V
VDCIN from High to Low, VBAT = 4.2V
70
10
120
40
170
70
mV
mV
VASD-USB
VUSBIN – VBAT Lockout Threshold
VUSBIN from Low to High
VUSBIN from High to Low
70
10
120
40
170
70
mV
mV
VENABLE
ENABLE Input Threshold Voltage
0.6
0.9
1.2
V
RENABLE
ENABLE Pulldown Resistance
VBDET
BATDET Input Threshold Voltage
From Low to High
IBATDET
BATDET Pull-Up Current
VBOC
●
1
2
3.5
MΩ
1.65
1.75
1.85
V
VBATDET = 0V
2
4
6
µA
BATDET Open Circuit Voltage
VDCIN = 5V, VUSBIN = 5V
4
4.2
4.4
V
VOL
Output Low Voltage
(⎯C⎯H⎯R⎯G, ⎯P⎯W⎯R)
ISINK = 5mA
0.12
0.35
V
ΔVRECHRG
Recharge Battery Threshold Voltage
VFLOAT – VRECHRG, 0°C < TA < 85°C
125
160
mV
2.25
4.1
6.75
ms
1
1.6
2.4
ms
90
tRECHRG
Recharge Comparator Filter Time
VBAT from High to Low
tTERMINATE
Termination Comparator Filter Time
IBAT Drops Below Termination Threshold
RON-DC
Power FET “ON” Resistance
(Between DCIN and BAT)
600
mΩ
RON-USB
Power FET “ON” Resistance
(Between USBIN and BAT)
700
mΩ
TLIM
Junction Temperature in ConstantTemperature Mode
120
°C
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 LTC4078X is guaranteed to meet the performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3: Failure to correctly solder the exposed backside of the package to
the PC board will result in a thermal resistance much higher than 40°C/W.
See Thermal Considerations.
Note 4: Supply current includes IDC and ITERM pin current (approximately
100µA each) but does not include any current delivered to the battery
through the BAT pin.
Note 5: Supply current includes IUSB and ITERM pin current
(approximately 100µA each) but does not include any current delivered to
the battery through the BAT pin.
4078xf
3
LTC4078X
TYPICAL PERFORMANCE CHARACTERISTICS
Regulated Output (Float) Voltage
vs Charge Current
Regulated Output (Float) Voltage
vs Temperature
4.220
VDCIN = VUSBIN = 5V
1.008
VDCIN = VUSBIN = 5V
1.006
4.22
4.210
1.004
4.205
1.002
4.20
RIDC = 1.24k
4.18
RIDC = RIUSB = 2k
VIDC (V)
4.215
4.200
0.998
4.14
4.190
0.996
4.12
4.185
0.994
4.10
100 200 300 400 500 600 700 800 900
IBAT (mA)
4.180
–10
10
30
50
TEMPERATURE (°C)
70
IUSB Pin Voltage vs Temperature
(Constant-Current Mode)
900
900
VDCIN = 5V
IBAT (mA)
1.000
0.998
700
600
500
RIDC = 2k
400
300
0.996
0.2
0.4
0.6
0.8
VIDC (V)
1.0
1.2
0
0.2
0.4
0.6
0.8
VIUSB (V)
4078x G05
⎯P⎯W⎯R Pin I-V Curve
1.0
1.2
4078x G06
⎯C⎯H⎯R⎯G Pin I-V Curve
60
VDCIN = VUSBIN = 5V
50
50
40
40
ICHRG (mA)
IPWR (mA)
RIUSB = 10k
0
0
4078x G04
60
RIUSB = 2k
100
0
90
400
200
RIDC = 10k
100
70
500
300
200
0.994
VUSBIN = 5V
RIUSB = 1.24k
RIDC = 1.24k
600
1.002
90
800
700
1.004
30
50
TEMPERATURE (°C)
70
Charge Current
vs IUSB Pin Voltage
800
1.006
10
30
50
TEMPERATURE (°C)
4078x G03
Charge Current
vs IDC Pin Voltage
VUSBIN = 5V
0.992
–10
10
4078x G02
4078x G01
1.008
0.992
–10
90
IBAT (mA)
0
VDCIN = 5V
1.000
4.195
4.16
VIUSB (V)
IDC Pin Voltage vs Temperature
(Constant-Current Mode)
4.24
VFLOAT (V)
VFLOAT (V)
4.26
TA = 25°C, unless otherwise specified.
30
30
20
20
10
10
0
VDCIN = VUSBIN = 5V
0
0
1
2
3
4
5
6
VPWR (V)
4078x G07
0
1
2
3
4
VCHRG (V)
5
6
4078x G08
4078xf
4
LTC4078X
TYPICAL PERFORMANCE CHARACTERISTICS
Charge Current
vs Ambient Temperature
Charge Current
vs Supply Voltage
1000
Charge Current vs Battery Voltage
900
900
1000
800
RIDC = 1.24k
800
800
700
700
RIDC = RIUSB = 2k
500
400
IBAT (mA)
600
600
IBAT (mA)
IBAT (mA)
TA = 25°C, unless otherwise specified.
500
400
300
300
200 V
DCIN = VUSBIN = 5V
100 VBAT = 4V
θJA = 30°C/W
0
70
50
30
90
–10 10
TEMPERATURE (°C)
200
0
4.0
130
110
4.5
5.0
5.5 6.0 6.5
VDCIN (V)
4078x G10
7.5
7.0
400
200
RIDC = 1.24k
VBAT = 4V
θJA = 30°C/W
100
600
VDCIN = VUSBIN = 5V
RIDC = 1.24k
θJA = 30°C/W
0
2.4
8.0
2.7
3.0
3.3 3.6
VBAT (V)
3.9
4.2
4078x G11
DCIN Power FET On-Resistance
vs Temperature
900
VBAT = 4V
IBAT = 200mA
750
850
700
800
600
1000
VBAT = 4V
IBAT = 200mA
VDCIN = VUSBIN = 5V
980
VENABLE (V)
750
700
550
10
30
50
TEMPERATURE (°C)
70
10
30
50
TEMPERATURE (°C)
70
4078x G13
60
VUSBIN = 5V
35
40
35
30
25
25
–25
0
25
50
TEMPERATURE (°C)
75
2.2
VDCIN = 5V
45
30
100
4078x G16
20
–50
90
2.3
RENABLE (MΩ)
IDCIN (µA)
VUSBIN = 4.3V
70
2.4
VENABLE = 5V
50
40
30
50
TEMPERATURE (°C)
ENABLE Pin Pulldown Resistance
vs Temperature
55
55
45
10
4078x G15
DCIN Shutdown Current
vs Temperature
VENABLE = 0V
20
–50
860
–10
90
4078x G14
USBIN Shutdown Current
vs Temperature
50
920
880
600
–10
90
940
900
650
500
–10
IUSBIN (µA)
ENABLE Pin Threshold Voltage
(On-to-Off) vs Temperature
960
650
60
4078x G12
USBIN Power FET On-Resistance
vs Temperature
RDS(ON) (mΩ)
RDS(ON) (mΩ)
800
4.5
VDCIN = 4.3V
2.1
2.0
1.9
1.8
1.7
–25
0
25
50
TEMPERATURE (°C)
75
100
4078x G17
1.6
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4078x G18
4078xf
5
LTC4078X
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold
vs Temperature
Overvoltage Lockout Threshold
vs Temperature
4.25
6.10
4.20
6.05
DCIN UVLO
4.15
6.00
VOV (V)
4.10
VUV (V)
TA = 25°C, unless otherwise specified.
4.05
4.00
DCIN OVLO
5.90
USBIN UVLO
3.95
USBIN OVLO
5.95
5.85
3.90
3.85
–10
10
30
50
TEMPERATURE (°C)
70
5.80
–10
90
10
30
50
TEMPERATURE (°C)
70
4078x G19
4078x G20
Recharge Threshold Voltage
vs Temperature
4.11
90
Battery Drain Current
vs Temperature
9.0
VDCIN = VUSBIN = 5V
VDCIN = VUSBIN = NOT CONNECTED
VBAT = 4.2V
8.5
8.0
IBAT (µA)
VRECHRG (V)
4.09
4.07
7.5
7.0
4.05
6.5
4.03
–10
10
30
50
TEMPERATURE (°C)
70
6.0
–50
90
–25
0
25
50
TEMPERATURE (°C)
75
4078x G21
100
4078x G22
BATDET Pin Threshold Voltage
(On-to-Off) vs Temperature
BATDET Voltage/Current
vs Temperature
4.4
2.0
VDCIN = VUSBIN = 5V
6.00
VDCIN = VUSBIN = 5V
1.9
VBOC
4.3
5.25
VBOC (V)
VBDET (V)
1.7
4.2
4.50
IBATDET
IBATDET (µA)
1.8
1.6
3.75
4.1
1.5
1.4
–10
10
30
50
TEMPERATURE (°C)
70
90
4078x G23
4.0
–10
3.00
10
30
50
TEMPERATURE (°C)
70
90
4078x G24
4078xf
6
LTC4078X
PIN FUNCTIONS
USBIN (Pin 1): USB Input Supply Pin. This input provides
power to the battery charger assuming a voltage greater
than VUVUSB and less than VOVUSB is present (typically
3.95V to 6V respectively). However, the DCIN input will
take priority if a voltage greater than VUVDC is present at
DCIN (typically 4.15V). The USBIN input allows charge
currents up to 850mA. This pin should be bypassed with
a 1µF capacitor.
IUSB (Pin 2): Charge Current Program for USB Power.
The charge current is set by connecting a resistor, RIUSB,
to ground. When charging in constant-current mode, this
pin servos to 1V. The voltage on this pin can be used to
measure the battery current delivered from the USB input
using the following formula:
IBAT =
VIUSB
• 1000
RIUSB
ITERM (Pin 3): Termination Current Threshold Program.
The termination current threshold, ITERMINATE, is set by
connecting a resistor, RITERM, to ground. ITERMINATE is set
by the following formula:
ITERMINATE =
100 V
RITERM
When the battery current, IBAT, falls below the termination
threshold, charging stops and the ⎯C⎯H⎯R⎯G output becomes
high impedance. This pin is internally clamped to approximately 1.5V. Driving this pin to voltages beyond the clamp
voltage should be avoided.
⎯ ⎯W⎯R (Pin 4): Open-Drain Power Supply Status Output.
P
When the DCIN or USBIN pin voltage is valid to begin charging (i.e. when the supply is greater than the undervoltage
lockout threshold, less than the overvoltage lockout threshold and at least 120mV above the battery terminal), the
⎯P⎯W⎯R pin is pulled low by an internal N-channel MOSFET.
Otherwise ⎯P⎯W⎯R is high impedance. This output is capable
of driving an LED.
⎯C⎯H⎯R⎯G (Pin 5): Open-Drain Charge Status Output. When
the LTC4078X is charging, the ⎯C⎯H⎯R⎯G pin is pulled low by
an internal N-channel MOSFET. When the charge cycle is
completed, ⎯C⎯H⎯R⎯G becomes high impedance. This output
is capable of driving an LED.
ENABLE (Pin 6): Enable Input. When the LTC4078X is
charging from the DCIN source, a logic low on this pin
enables the charger. When the LTC4078X is charging
from the USBIN source, a logic high on this pin enables
the charger. If this input is left floating, an internal 2MΩ
pulldown resistor defaults the LTC4078X to charge when
a wall adapter is applied and to shut down if only the USB
source is applied.
BATDET (Pin 7): Battery Detection Input. When the voltage on this pin falls below VBDET (typically 1.75V), the
charger is on and ready for charging a battery. If this
input is left floating, an internal pull-up resistor will disable charging.
IDC (Pin 8): Charge Current Program for Wall Adapter
Power. The charge current is set by connecting a resistor, RIDC, to ground. When charging in constant-current
mode, this pin servos to 1V. The voltage on this pin can
be used to measure the battery current delivered from the
DC input using the following formula:
IBAT =
VIDC
• 1000
RIDC
BAT (Pin 9): Battery Charger Output. This pin provides
charge current to the battery and regulates the final float
voltage to 4.2V.
DCIN (Pin 10): Wall Adapter Input Supply Pin. This input
provides power to the battery charger assuming a voltage
greater than VUVDC and less than VOVDC is present (typically 4.15V to 6V respectively). A valid voltage on the DCIN
input will always take priority over the USBIN input. The
DCIN input allows charge currents up to 950mA. This pin
should be bypassed with a 1µF capacitor.
Exposed Pad (Pin 11): GND. The exposed backside of the
package is ground and must be soldered to PC board ground
for electrical connection and maximum heat transfer.
4078xf
7
LTC4078X
BLOCK DIAGRAM
DCIN
BAT
USBIN
10
9
1
CC/CV
REGULATOR
CC/CV
REGULATOR
VBOC
DC_ENABLE
USB_ENABLE
CHARGER CONTROL
+
7 BATDET
DISABLE
PWR
–
4
+
4.15V
BAT
6V
ENABLE
–
+
USBIN UVLO
DCIN UVLO
+
–
–
+
+
DCIN OVLO
USBIN OVLO
+
6
–
+
–
1.75V
–
3.95V
BAT
6V
+
TDIE
–
120°C
2M
0.9V
CHRG
–
4.075V
+
BAT
–
THERMAL
REGULATION
RECHARGE
–
5
0.1V
IBAT/1000
TERMINATION
IBAT/1000
IBAT/1000
+
GND
11
ITERM
3
IDC
RITERM
IUSB
2
8
RIDC
4078X BD
RIUSB
4078xf
8
LTC4078X
OPERATION
The LTC4078X is designed to efficiently manage charging of a single-cell lithium-ion battery from two separate
power sources: a wall adapter and USB power bus. Using the constant-current/constant-voltage algorithm, the
charger can deliver up to 950mA of charge current from
the wall adapter supply or up to 850mA of charge current
from the USB supply with a final float voltage accuracy of
±0.6%. The LTC4078X has two internal P-channel power
MOSFETs and thermal regulation circuitry. No blocking
diodes or external sense resistors are required.
Charge current out of the BAT pin can be determined at
any time by monitoring the IDC or IUSB pin voltage and
applying the following equations:
Power Source Selection
By default, the BATDET pin is pulled high with an internal
resistor, disabling the charger. To enable the charger, the
BATDET pin must be pulled below the VBDET threshold
(typically 1.75V). An external resistor to ground less than
100k (typically 3.9k) located in the battery pack is used to
detect battery presence.
The LTC4078X can charge a battery from either the wall
adapter input or the USB port input. The LTC4078X automatically senses the presence of voltage at each input. If
both power sources are present, the LTC4078X defaults to
the wall adapter source provided a valid voltage is present
at the DCIN input. “Valid voltage” is defined as:
• Supply voltage is greater than the UVLO threshold
and less than the OVLO threshold.
• Supply voltage is greater than the battery voltage by
40mV.
The open-drain power status output (⎯P⎯W⎯R) indicates
which power source has been selected. Table 1 describes
the behavior of this status output.
Programming and Monitoring Charge Current
The charge current delivered to the battery from the wall
adapter or USB supply is programmed using a single resistor from the IDC or IUSB pin to ground. Both program
resistors and charge currents (ICHRG) are calculated using
the following equations:
RIDC =
1000 V
ICHRG−DC
RIUSB =
, ICHRG−DC =
1000 V
ICHRG−USB
1000 V
RIDC
, ICHRG−USB =
1000 V
RIUSB
IBAT =
VIDC
• 1000, (ch arg ing from wall adapter )
RIDC
IBAT =
VIUSB
• 1000, (ch arg ing from USB sup ply)
RIUSB
Battery Detection
Programming Charge Termination
The charge cycle terminates when the charge current
falls below the programmed termination threshold level
during constant-voltage mode. This threshold is set by
connecting an external resistor, RITERM, from the ITERM
pin to ground. The charge termination current threshold
(ITERMINATE) is set by the following equation:
RITERM =
100 V
ITERMINATE
, ITERMINATE =
100 V
RITERM
The termination condition is detected by using an internal
filtered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV* for longer than
tTERMINATE (typically 1.6ms), charging is terminated. The
charge current is latched off and the LTC4078X enters
standby mode.
When charging, transient loads on the BAT pin can cause
the ITERM pin to fall below 100mV for short periods of
time before the DC charge current has dropped below the
*Any external sources that hold the ITERM pin above 100mV will prevent the LTC4078X from
terminating a charge cycle.
4078xf
9
LTC4078X
OPERATION
logic low enables the charger and logic high disables it (the
pulldown defaults the charger to the charging state). The
opposite is true when the USB input is supplying power;
logic low disables the charger and logic high enables it
(the default is the shutdown state).
programmed termination current. The 1.6ms filter time
(tTERMINATE) on the termination comparator ensures that
transient loads of this nature do not result in premature
charge cycle termination. Once the average charge current
drops below the programmed termination threshold, the
LTC4078X terminates the charge cycle and stops providing
current out of the BAT pin. In this state, any load on the
BAT pin must be supplied by the battery.
The DCIN input draws 40µA when the charger is in shutdown mode. The USBIN input draws 40µA during shutdown
if no voltage is applied to DCIN, but draws only 23µA when
VDCIN provides valid voltage (see Table 1).
Automatic Recharge
Status Indicators
In standby mode, the charger sits idle and monitors the
battery voltage using a comparator with a 4.1ms filter time
(tRECHRG). A charge cycle automatically restarts when the
battery voltage falls below 4.075V (which corresponds to
approximately 80% to 90% battery capacity). This ensures
that the battery is kept at, or near, a fully charged condition and eliminates the need for periodic charge cycle
initiations.
The charge status open-drain output (⎯C⎯H⎯R⎯G) has two
states: pulldown and high impedance. The pulldown state
indicates that the LTC4078X is in a charge cycle. Once the
charge cycle has terminated or the LTC4078X is disabled,
the pin state becomes high impedance.
The power supply status open-drain output (⎯P⎯W⎯R) has
two states: pulldown and high impedance. The pulldown
state indicates that power is present at either DCIN or
USBIN. This output is strong enough to drive an LED. If
no valid voltage is applied at either pin, the ⎯P⎯W⎯R pin is
high impedance, indicating that the LTC4078X lacks valid
input voltage (see Table 1) to charge the battery.
Manual Shutdown
The ENABLE pin has a 2MΩ pulldown resistor to GND. The
definition of this pin depends on which source is supplying
power. When the wall adapter input is supplying power,
Table 1. Power Source Selection (VBATDET < 1.75V)
VUSBIN < 3.95V or
VUSBIN < BAT + 50mV
ENABLE
HIGH
LOW or No Connect
6V > VUSBIN > 3.95V and
VUSBIN > BAT + 50mV
HIGH
LOW or No Connect
22V > VUSBIN > 6V
HIGH
LOW or No Connect
VDCIN < 4.15V or
No Charging.
VDCIN < BAT + 50mV ⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
6V > VDCIN > 4.15V
and VDCIN > BAT +
50mV
No Charging.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: Hi-Z
Charging from DCIN No Charging.
⎯P⎯WR
⎯ : LOW
source.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯RG
⎯ : Hi-Z
⎯C⎯H⎯R⎯G: LOW
Charging from DCIN No Charging.
⎯P⎯WR
⎯ : LOW
source.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯RG
⎯ : Hi-Z
⎯C⎯H⎯R⎯G: LOW
Charging from DCIN
source.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: LOW
22V > VDCIN > 6V
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
Charging from
USBIN source.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: LOW
No Charging.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: LOW
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
No Charging.
⎯P⎯W⎯R: Hi-Z
⎯C⎯H⎯R⎯G: Hi-Z
4078xf
10
LTC4078X
OPERATION
Thermal Limiting
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise
above a preset value of approximately 120°C. This feature
protects the LTC4078X from excessive temperature and
allows the user to push the limits of the power handling
capability of a given circuit board without risk of damag-
DCIN POWER REMOVED
ing the device. The charge current can be set according
to typical (not worst-case) ambient temperature with the
assurance that the charger will automatically reduce the
current in worst case conditions. DFN package power
considerations are discussed further in the Applications
Information section.
NO POWER
USB POWER REMOVED
POWER APPLIED
ENABLE = LOW
ENABLE = HIGH
YES
DCIN > 4.15V
AND DCIN > BAT
NO
6V > DCIN > 4.15V
AND DCIN > BAT
NO
NO
YES
YES
NO
BATDET < 1.75V
YES
6V > USBIN > 3.95V
AND USBIN > BAT
NO
BATDET < 1.75V
YES
CHARGE MODE
(DCIN)
CHARGE MODE
(USBIN)
FULL CURRENT
FULL CURRENT
CHRG STATE: PULLDOWN
CHRG STATE: PULLDOWN
IBAT < ITERMINATE
IN VOLTAGE MODE
IBAT < ITERMINATE
IN VOLTAGE MODE
STANDBY MODE
(DCIN)
STANDBY MODE
(USBIN)
NO CHARGE CURRENT
NO CHARGE CURRENT
CHRG STATE: Hi-Z
CHRG STATE: Hi-Z
SHUTDOWN MODE
(DCIN)
SHUTDOWN MODE
(USBIN)
CHRG STATE: Hi-Z
CHRG STATE: Hi-Z
BAT < 4.075V
BAT < 4.075V
4078X F01
Figure 1. LTC4078X State Diagram of a Charge Cycle
4078xf
11
LTC4078X
APPLICATIONS INFORMATION
Using a Single Charge Current Program Resistor
Stability Considerations
The LTC4078X can program the wall adapter charge current
and USB charge current independently using two program
resistors, RIDC and RIUSB. Figure 2 shows a charger circuit
that sets the wall adapter charge current to 800mA and
the USB charge current to 500mA.
The constant-voltage mode feedback loop is stable without
any compensation provided a battery is connected to the
charger output. However, a 1µF capacitor with a 1Ω series
resistor is recommended at the BAT pin to keep the ripple
voltage low when the battery is disconnected.
In applications where the programmed wall adapter
charge current and USB charge current are the same, a
single program resistor can be used to set both charge
currents. Figure 3 shows a charger circuit that uses one
charge current program resistor.
When the charger is in constant-current mode, the charge
current program pin (IDC or IUSB) is in the feedback loop,
not the battery. The constant-current mode stability is affected by the impedance at the charge current program pin.
With no additional capacitance on this pin, the charger is
stable with program resistor values as high as 20k (ICHRG
= 50mA); however, additional capacitance on these nodes
reduces the maximum allowed program resistor.
USB
PORT
C1
1µF
800mA (WALL)
500mA (USB)
LTC4078X
WALL
ADAPTER
BAT
DCIN
USBIN BATDET
C2, 1µF
R1
2k
1%
+
R4
3.9k
IUSB
IDC
ITERM
GND
R2
1.24k
1%
R3
2k
1%
4.2V
Li-Ion
BATTERY
PACK
4078X F02
Figure 2. Dual Input Charger with Independent Charge Currents
LTC4078X
WALL
ADAPTER
USB
PORT
C1
1µF
DCIN
500mA
BAT
USBIN BATDET
C2, 1µF
+
R4
3.9k
IUSB
IDC
R1
2k
1%
ITERM
GND
R3
2k
1%
4.2V
Li-Ion
BATTERY
PACK
4078X F03
Figure 3. Dual Input Charger Circuit. The Wall Adapter
Charge Current and USB Charge Current Are Both
Programmed to Be 500mA
In this circuit, the programmed charge current from both the
wall adapter supply is the same value as the programmed
charge current from the USB supply:
ICHRG−DC = ICHRG−USB =
1000 V
RISET
Power Dissipation
When designing the battery charger circuit, it is not necessary to design for worst-case power dissipation scenarios
because the LTC4078X automatically reduces the charge
current during high power conditions. The conditions that
cause the LTC4078X to reduce charge current through
thermal feedback can be approximated by considering the
power dissipated in the IC. Most of the power dissipation
is generated from the internal charger MOSFET. Thus, the
power dissipation is calculated to be:
PD = (VIN – VBAT) • IBAT
PD is the dissipated power, VIN is the input supply voltage (either DCIN or USBIN), VBAT is the battery voltage
and IBAT is the charge current. The approximate ambient
temperature at which the thermal feedback begins to
protect the IC is:
TA = 120°C – PD • θJA
TA = 120°C – (VIN – VBAT) • IBAT • θJA
Example: An LTC4078X operating from a 5V wall adapter
(on the DCIN input) is programmed to supply 800mA
full-scale current to a discharged Li-Ion battery with a
voltage of 3.3V.
4078xf
12
LTC4078X
APPLICATIONS INFORMATION
Assuming θJA is 40°C/W (see Thermal Considerations),
the ambient temperature at which the LTC4078X will begin
to reduce the charge current is approximately:
800mA to a battery from a 5V supply at room temperature.
Without a good backside thermal connection, this number
would drop to much less than 500mA.
TA = 120°C – (5V – 3.3V) • (800mA) • 40°C/W
Input Capacitor Selection
TA = 120°C – 1.36W • 40°C/W = 120°C – 54.4°C
When an input supply is connected to a portable product,
the inductance of the cable and the high-Q ceramic input
capacitor form an L-C resonant circuit. While the LTC4078X
is capable of withstanding input voltages as high as 22V,
if the input cable does not have adequate mutual coupling
or if there is not much impedance in the cable, it is possible for the voltage at the input of the product to reach
as high as 2x the input voltage before it settles out. To
prevent excessive voltage from damaging the LTC4078X
during a hot insertion, it is best to have a low voltage coefficient capacitor at the input pins to the LTC4078X. This is
achievable by selecting an X5R or X7R ceramic capacitor
that has a higher voltage rating than that required for the
application. For example, if the maximum expected input
voltage is 15V, a 25V X5R 1µF capacitor would be a better
choice than the smaller 16V X5R capacitor. Note that no
charging will occur with 15V in.
TA = 65.6°C
The LTC4078X can be used above 65.6°C ambient, but
the charge current will be reduced from 800mA. The approximate current at a given ambient temperature can be
approximated by:
IBAT =
120 °C – TA
( VIN – VBAT ) • θ JA
Using the previous example with an ambient temperature
of 75°C, the charge current will be reduced to approximately:
120 °C – 75 °C
45 °C
=
(5V – 3 . 3V) • 40 °C / W 68 °C / A
= 662mA
IBAT =
IBAT
It is important to remember that LTC4078X applications do
not need to be designed for worst-case thermal conditions,
since the IC will automatically reduce power dissipation
when the junction temperature reaches approximately
120°C.
Using a tantalum capacitor or an aluminum electrolytic
capacitor for input bypassing, or paralleling with a ceramic
capacitor will also reduce voltage overshoot during a hot
insertion. Ceramic capacitors with Y5V or Z5U dielectrics
are not recommeded.
Alternatively, the following soft connect circuit can be
employed (as shown in Figure 4).
Thermal Considerations
In order to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on the
backside of the LTC4078X DFN package is properly soldered to the PC board ground. When correctly soldered to
a 2500mm2 double sided 1oz copper board, the LTC4078X
has a thermal resistance of approximately 40°C/W. Failure
to make thermal contact between the exposed pad on the
backside of the package and the copper board will result
in thermal resistances far greater than 40°C/W. As an
example, a correctly soldered LTC4078X can deliver over
DCIN/USBIN
R1
40k
+15V
INPUT INPUT CABLE
C2
100nF
C1
1µF
LTC4078X
MN1
GND
4078X F04
Figure 4. Input Soft Connect Circuit
4078xf
13
LTC4078X
APPLICATIONS INFORMATION
In this circuit, capacitor C2 holds MN1 off when the cable
is first connected. Eventually C2 begins to charge up to the
USB input voltage applying increasing gate drive to MN1.
The long time constant of R1 and C1 prevent the current
from rapidly building up in the cable, thus dampening out
any resonant overshoot.
Reverse Polarity Input Voltage Protection
In some applications, protection from reverse polarity
voltage on the input supply pins is desired. With sufficient
supply voltage, a series blocking diode can be used. In
other cases where the voltage drop must be kept low, a
P-channel MOSFET can be used (as shown in Figure 5).
DRAIN-BULK
DIODE OF FET
LTC4078X
WALL
ADAPTER
DCIN
4078X F05
Figure 5. Low Loss Reverse Polarity Protection
4078xf
14
LTC4078X
PACKAGE DESCRIPTION
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.25 ± 0.05
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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 SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
4078xf
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.
15
LTC4078X
TYPICAL APPLICATION
Full Featured Li-Ion Charger
800mA (WALL)
475mA (USB)
LTC4078X
WALL
ADAPTER
USB
POWER
DCIN
BAT
1k
USBIN
1µF
IUSB
IDC
2.1k
1%
1k
1µF
1.24k
1%
PWR
CHRG
BATDET
ITERM
GND
3.9k
1k
1%
+
4.2V Li-Ion
BATTERY
PACK
4078X TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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Dual Input Standalone Li-Ion Battery Charger
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Programmable C or C/x USB Charge Current for Low Power USB Operation,
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LTC4085
USB Power Manager with Ideal Diode Controller
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LTC4089/
LTC4089-5
USB Power Manager with Ideal Diode Controller
and High Efficiency Li-Ion Battery Charger
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ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
4078xf
16 Linear Technology Corporation
LT 0907 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007