Freescale Semiconductor
Advance Information
Document Number: MC34671
Rev. 1.0, 01/2008
High Input Voltage 600mA
Charger for Single-cell Li-Ion
Batteries
34671
The MC34671 is a cost-effective fully-integrated battery charger for
POWER MANAGEMENT IC
Li-Ion or Li-Polymer batteries. The high input voltage, up to 28V,
eliminates the input over-voltage-protection circuit required in
handheld devices such as cell phones, Bluetooth accessories and MP3
players.
A typical charge cycle includes trickle, constant-current (CC) and
constant-voltage (CV) charge modes. The CC-mode current is
programmable up to 600mA with an external resistor. The voltage
across the external resistor is also used to monitor the actual charge
EP SUFFIX (PB-FREE)
98ASA10774D
current. The constant voltage is fixed at 4.2V with 0.7% accuracy over
8-PIN UDFN
a -20°C to 70°C temperature range. The trickle-mode current is preset
to 20% of the CC-mode current when the battery voltage is lower than
the trickle-mode threshold. The end-of-charge (EOC) current threshold
is preset to 10% of the CC-mode current to save the board space and
ORDERING INFORMATION
cost. A charge current thermal foldback feature limits the charge
current when the IC internal temperature rises to a preset threshold.
Temperature
Device
Package
Range (TA)
The MC34671 also protects the system with its input over-voltage
protection (OVP) feature. In addition, the MC34671 has a 2.6V falling
MC34671AEP/R2
-40°C to 85°C
8-UDFN
power-on-reset (POR) threshold, making it perfect to work with current
limited power supplies. Three indication pins (PPR, CHG and FAST)
can be simply interfaced to a microprocessor or LEDs. When no power supply is connected, or when disabled, the charger draws
less than 1.0µA leakage current from the battery.
Features
• No external MOSFET, reverse-blocking diode or current-sense resistor are required
• Guaranteed maximum 600mA programmable CC-mode current
• ±0.7% voltage accuracy over -20°C to 70°C
• ±5% current accuracy over -40°C to 85°C
• 28V maximum voltage for the power input with 11V over-voltage protection threshold
• 2.6V minimum input operating voltage
• Trickle charge for fully discharged batteries
• Charge current monitor
• Charge current thermal foldback
• Pb-free packaging designated by suffix code EP
34671
VIN
CIN
VIN
GND
CHG
ON
OFF
TO BATTERY
BAT
COUT
ISET
RISET
VIO
PPR
EN
FAST
Figure 1. 34671 Simplified Application Diagram
* This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Freescale Semiconductor, Inc., 2007-8. All rights reserved.
TO MCU
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
VIN
BAT
–
VIN
Monitor
Internal
Supply
+
VREF
Charge
Control
REF
ISET
–
PPR
+
VOS
IREF
VIN + –
+
BAT
–
–
+
Die
Temp
110°C
CHG
EN
Logic
Control
+
–
IEOC
FAST
GND
Figure 2. 34671 Simplified Internal Block Diagram
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Analog Integrated Circuit Device Data
Freescale Semiconductor
PIN CONNECTIONS
PIN CONNECTIONS
VIN
1
8
BAT
PPR
2
7
ISET
CHG
3
6
FAST
EN
4
5
GND
EPAD
Figure 3. 34671 Pin Connections
Table 1. 34671 Pin Definitions
A functional description of each pin can be found in the Functional Pin Description section beginning on page 11.
Pin Number
Pin Name
Pin Function
Formal Name
Definition
1
VIN
Input
Input supply
2
PPR
Output
Power present
indicator
3
CHG
Output
Charge indicator
4
EN
Input
Enable
Enable logic input.
5
GND
Ground
Ground
Ground.
6
FAST
Output
Fast charge indicator
7
ISET
Output
CC-mode current
setting and charge
current monitor
8
BAT
Output
Charger output
EPAD
EPAD
N/A
Exposed pad
The supply input.
Indication of the input power status. Open drain output.
Indication of the charge status. Open drain output.
Indication of the fast charge status. Open drain output.
CC-mode current setting and monitoring pin.
The charger output pin. Connect this pin to the Li-Ion battery.
Exposed pad for thermal dissipation enhancement. Must be soldered on
the large ground plane on the PCB to increase the thermal dissipation.
The pad must be connected to GND electrically.
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Analog Integrated Circuit Device Data
Freescale Semiconductor
3
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 2. Maximum Ratings
All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or
permanent damage to the device.
Ratings
Symbol
Value
Unit
ELECTRICAL RATINGS
Input Voltage Range
V
VIN Pin
VIN
PPR and CHG Pins
EN, BAT, ISET, and FAST Pins
-0.3 to 28
VPPR, VCHG
-0.3 to 12
VEN, VBAT,
VISET, VFAST
-0.3 to 5.5
ESD Voltage(1)
V
Human Body Model (HBM)
VESD
Machine Model (MM)
±2000
±200
THERMAL RATINGS
Operating Temperature
°C
Ambient
TA
-40 to 85
Junction
TJ
-40 to 150
TSTG
-65 to 150
RθJC
10
RθJA
70
TPPRT
Note 4
Storage Temperature
Thermal
Resistance(2)
°C/W
Junction-to-Case
Junction-to-Ambient
Peak Package Reflow Temperature During
°C
Reflow(3),(4)
°C
Notes
1. ESD testing is performed in accordance with the Human Body Model (HBM) (CZAP = 100pF, RZAP = 1500Ω), and the Machine Model
(MM) (CZAP = 200pF, RZAP = 0Ω).
2.
3.
4.
Device mounted on the Freescale EVB test board per JEDEC DESD51-2.
Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
Freescale’s Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow
Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes
and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics.
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Analog Integrated Circuit Device Data
Freescale Semiconductor
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics
Characteristics noted under conditions VIN = 5.0V, -40°C ≤ TA ≤ 85°C, CIN = 1.0µF, COUT = 2.2µF (see Figure 1), unless
otherwise noted. Typical values noted reflect the approximate parameter means at VIN = 5.0V and TA = 25°C under nominal
conditions, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
Input Voltage Range(5)
VIN
2.6
-
10
V
VIN Pin Supply Current
IIN
Charger enabled(6)
-
1400
-
Charger disabled
-
-
350
POWER INPUT
Regulated Output Voltage
µA
VBAT
V
VIN = 5.0V; IBAT = 10mA; TA = 25°C
4.185
4.20
4.215
VIN = 5.0V; IBAT = 10mA; TA = -20 to 70°C
4.170
4.20
4.230
VIN = 5.0V; IBAT = 10mA; TA = -40 to 85°C
4.158
4.20
4.230
-
500
700
Power MOSFET On Resistance
RDS(ON)
VBAT = 4V; IBAT = 500mA; ICHG = 600mA
BAT Pin Standby Current
mΩ
ISTDBY
VIN not powered or charger disabled
µA
-
-
1.0
Rising VIN threshold
3.0
-
3.9
Falling VIN threshold
-
2.4
2.6
Rising threshold
-
-
60
Falling threshold
1.0
-
22
VOVP
10
11
12
V
VOVPHYS
-
400
-
mV
Constant Current Mode Charge Current Range(7)
ICHG
50
-
600
mA
ICHG Accuracy
ICHG
Power On Reset
VPOR
VIN-BAT Offset Voltage
V
VOS
Over-voltage Protection Rising Threshold
Over-voltage Protection Threshold Hysteresis
mV
CHARGE CURRENT
For ICHG between 300mA to 600mA
(7)
For ICHG between 50mA to 300mA (Tested at 300mA)
Trickle-mode Charge Current
ITRKL
End-of-Charge (EOC) Threshold
IEOC
When ICHG is set to 300mA
ISET Pin Voltage for ICHG Reference(7)
VISET
%
95
100
105
90
100
110
16
20
24
20
30
40
-
1.0
-
% ICHG
mA
V
Notes
5. Refer to the Power-on-Reset parameter for VIN turn on and turn off values.
6.
7.
Supply current does not include the current delivered to the battery through the BAT pin.
Not tested. Guaranteed by design.
34671
Analog Integrated Circuit Device Data
Freescale Semiconductor
5
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 5.0V, -40°C ≤ TA ≤ 85°C, CIN = 1.0µF, COUT = 2.2µF (see Figure 1), unless
otherwise noted. Typical values noted reflect the approximate parameter means at VIN = 5.0V and TA = 25°C under nominal
conditions, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
VTRKL
2.6
2.7
2.8
V
VTRKLHYS
40
100
150
mV
VRECH
4.060
4.100
4.140
V
VTHRCHG
-
25
50
mV
EN Input High Threshold Voltage
VIH
1.5
-
-
V
EN Input Low Threshold Voltage
VIL
-
-
0.5
V
EN Input Leakage Current
IEN
-
2.0
7.5
µA
-
mA
12
15
CHARGE THRESHOLDS
Trickle-mode Rising Threshold Voltage
Trickle-mode Threshold Voltage Hysteresis
Recharge Falling Threshold Voltage
Recharge Threshold Voltage Hysteresis
LOGIC INPUT AND OUTPUT
VEN = 3.0V
PPR and CHG Sink Current When the Output is Low
IPCSINKL
VCHG =VPPR = 0.6V
PPR and CHG Leakage Current When the Output is High-impedance
IPCLEAKH
VCHG =VPPR = 5.0V
FAST Sink Current When the Output is Low
-
-
1.0
0.3
-
-
-
-
1.0
95
110
125
IFSINKL
VFAST = 0.5.0V
FAST Leakage Current When the Output is High-impedance
µA
mA
IFLEAKH
VFAST = 3.0V
µA
CHARGE CURRENT THERMAL FOLDBACK
Current Foldback Die Temperature Limit
TLIMIT
°C
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Analog Integrated Circuit Device Data
Freescale Semiconductor
ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Dynamic Electrical Characteristics
Characteristics noted under conditions VIN = 5.0V, -40°C ≤ TA ≤ 85°C, CIN = 1µF, COUT = 2.2µF (Figure 1), unless otherwise
noted. Typical values noted reflect the approximate parameter means at VIN = 5.0V and TA = 25°C under nominal conditions,
unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
tEOC
6.0
8.0
10
ms
fOSC
40.0
50.0
60.0
kHz
END OF CHARGE
EOC Filter Time
OSCILLATOR
Oscillation Frequency
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Analog Integrated Circuit Device Data
Freescale Semiconductor
7
ELECTRICAL CHARACTERISTICS
ELECTRICAL PERFORMANCE CURVES
Battery Voltage (V)
4.5
300
Battery Voltage
4.0
250
3.5
200
3.0
150
2.5
100
Charge Current
2.0
1.5
0
20
40
60
80
50
Charge Current (mA)
350
5.0
0
100 120
Constant Charge Current (mA)
ELECTRICAL PERFORMANCE CURVES
350
300
RISET=8.80 kΩ
250
200
150
RISET=17.8 kΩ
100
50
0
4
5
6
7
8
VIN (V)
Charge Time ( min)
Figure 4. Complete Charge Cycle
VIN = 5.0V, ICHG=300mA, TA = 25°C
VBAT ( V)
4.1
4.0
3.9
3.8
3.7
3.6
6
7
8
9
10
11
Trickle Charge Current (mA)
4.2
5
80
70
60
50
RISET=8.80 kΩ
40
30
20
RISET=17.80 kΩ
10
0
4
5
6
VIN (V)
7
8
9
10
VIN (V)
Figure 5. VBAT vs VIN
IBAT = 0mA, TA = 25°C
Figure 8. Trickle Charge Current vs VIN
VBAT = 2.0V, TA = 25°C
1.2
2400
1.0
2000
VISET (V)
VIN Pin Supply Current ( µA)
10
Figure 7. Constant Charge Current vs VIN
VBAT = 3.0V, TA = 25°C
4.3
3.5
4
9
1600
Charger Enabled
1200
800
0.6
0.4
400
0
0.8
0.2
Charger Disabled
3
4
5
6
7
8
9
10
VIN (V)
Figure 6. VIN Pin Supply Current vs VIN
IBAT = 0mA, TA = 25°C
11
0.0
5
6
7
8
9
10
VIN (V)
Figure 9. VISET vs VIN
VBAT = 3.9V, TA = 25°C
34671
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Analog Integrated Circuit Device Data
Freescale Semiconductor
1.2
VISET (V)
1.0
RISET=4.36 kΩ
RISET=8.80 kΩ
0.8
0.6
0.4
0.2
0.0
0
100
200
300
400
500
600
Constant Charge Current (mA)
ELECTRICAL CHARACTERISTICS
ELECTRICAL PERFORMANCE CURVES
700
RISET=4.27 kΩ
600
500
400
RISET=8.51 kΩ
300
200
RISET=17.21 kΩ
100
0
-40
-20
Charge Current (mA)
Trickle Charge Current (mA)
Charge Current (mA)
250
200
150
RISET=17.80 kΩ
50
1
2
80
3
4
150
RISET=4.27 kΩ
125
100
75
RISET=8.51 kΩ
50
RISET=17.21 kΩ
25
0
-40
-20
0
20
40
60
80
o
VBAT (V)
Temperature ( C)
Figure 14. Trickle Charge Current vs Temperature
VIN = 5.0V, VBAT = 2.0V
Figure 11. Charge Current vs VBAT
VIN = 5.0V, TA = 25°C
1.2
4.30
1.0
4.25
0.8
4.20
VISET (V)
VBAT (V)
60
Temperature ( C)
RISET=8.80 kΩ
0
40
Figure 13. Constant Charge Current vs Temperature
VIN = 5.0V, VBAT = 3.9V
350
100
20
o
Figure 10. VISET vs Charge Current
VIN = 5.0V, TA = 25°C
300
0
4.15
4.10
0.6
0.4
0.2
4.05
4.00
-40
-20
0
20
40
o
Temperature ( C)
Figure 12. VBAT vs Temperature
VIN = 5.0V, IBAT = 0mA
60
80
0.0
-40
-20
0
20
40
60
80
o
Temperature ( C)
Figure 15. VISET vs Temperature
VIN = 5.0V
34671
Analog Integrated Circuit Device Data
Freescale Semiconductor
9
ELECTRICAL CHARACTERISTICS
ELECTRICAL PERFORMANCE CURVES
RDS(ON) ( mΩ)
550
500
450
400
350
300
-40
-20
0
20
40
60
80
BAT Pin Supply Current ( µA)
600
1.0
0.8
0.6
0.4
0.2
0.0
-40
-20
40
60
80
Figure 18. BAT Pin Supply Current vs Temperature
VBAT = 5.0V, VIN Not Powered or Charger Disabled
2000
4.20
4.15
4.10
4.05
4.00
3.95
-20
0
20
40
60
80
o
Temperature ( C)
Figure 17. Recharge Voltage Threshold vs Temperature
RISET = 17.21kΩ, VIN = 5.0V
VIN Pin Supply Current ( µA)
Recharge Voltage Threshold (V)
20
Temperature ( C)
Temperature ( C)
Figure 16. RDS(ON) vs Temperature
VBAT = 4.0V, ICHG=300mA, IBAT= 250mA
3.90
-40
0
o
o
1750
Charger Enabled
1500
1250
1000
750
500
Charger Disabled
250
0
-40
-20
0
20
40
60
80
o
Temperature ( C)
Figure 19. VIN Pin Supply Current vs Temperature
VIN = 5.0V
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10
Analog Integrated Circuit Device Data
Freescale Semiconductor
FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The MC34671 is a fully-integrated Li-Ion and Li-Polymer
battery charger in a tiny package. It uses current, voltage and
temperature control loops to regulate the charge current. It
has up to a 28V input voltage rating, which makes the
handheld device safe even when connected to a wrong AC
adapter.
The MC34671 requires only two external capacitors and
one resistor to build a fully functional charger for spacelimited applications such as cell phones, Bluetooth
accessories and MP3 players. Its ultra high-accuracy
(±0.7%) output voltage and temperature-limited charging
current offer additional battery safety during charging.
The CC-mode current can be programmed with an
external resistor (RISET). The voltage across this resistor is
proportional to the charge current, so the system can monitor
the charge current during the whole charge cycle. The EOC
current threshold is preset to 10% of the CC-mode current.
For a deeply discharged battery with a voltage lower than
2.7V, the MC34671 charges the battery with a trickle-mode
current, which is 20% of the CC-mode current.
Three indication outputs make it easy to report the input
power status and the charge status to MCUs, or users via
LEDs.
FUNCTIONAL PIN DESCRIPTION
INPUT SUPPLY (VIN)
The supply input. This pin should be bypassed to ground
with a 1.0µF capacitor.
POWER PRESENT INDICATOR (PPR)
Open-drain logic output to indicate the input-power status.
The PPR pin output is only determined by the input voltage,
not other conditions such as the EN pin input. The output is
low if VIN is higher than VPOR. This pin is capable to sink at
least 12.0mA of current to drive an LED indicator.
CHARGE INDICATOR (CHG)
Open-drain logic output to indicate the charge status. The
output is low when the MC34671 is charging, until the EOC
conditions are reached. This pin is capable to sink at least
12.0mA of current to drive an LED indicator.
ENABLE (EN)
Active low enable logic Input. This pin is internally pulled to
ground by a weak current source. When left floating, the
charger is enabled. Pulling this pin to a high voltage,
externally disables the charger.
GROUND (GND)
mode threshold. This pin is capable to sink more than 0.3mA
of current. When the charger is on, this pin outputs a logic low
signal if the battery voltage is higher than the trickle-mode
threshold. When the charger is in the shutdown mode or in
any fault conditions, this pin outputs a high-impedance.
CC-MODE CURRENT SETTING AND CHARGE
CURRENT MONITOR (ISET)
The CC-mode current, ICHG, is programmed by connecting
a resistor, RISET, between this pin and the ground. When
charging in the CC-mode, the voltage at this pin is 1.0V. The
voltage reduces proportionally as the charge current reduces
in the CV-mode. During the whole charge cycle, the voltage
at this pin can be used to monitor the charge current using the
following equation:
V ISET
I BAT = --------------- ⋅ I CHG
1.0V
equ. 1
where IBAT is the actual charge current, ICHG is the
programmed CC-mode current, and VISET is the voltage of
the ISET pin during the whole charge cycle.
CHARGER OUTPUT (BAT)
Charger output pin. Connect this pin to the battery being
charged. Bypass to ground with a 2.2µF or higher capacitor.
Ground.
FAST CHARGE INDICATOR (FAST)
When charging, this open-drain logic output indicates
whether or not the battery voltage is higher than the trickle-
EXPOSED PAD (EPAD)
Exposed pad. It must be soldered on the large ground
plane of the PCB to enhance the thermal conductivity. The
pad must be connected to GND electrically.
34671
Analog Integrated Circuit Device Data
Freescale Semiconductor
11
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34671 - Functional Block Diagram
Integrated Supply
Internal Supply & Reference
Sensing & Control
VIN Monitor
Charge Control
Current Setting
End of Charge
Current Monitor
VIN - BAT Compare
Power MOSFET
Die Temperature Feedback
Logic
Logic Control
Status Indication
Integrated Supply
Sensing & Control
Logic
MOSFET
Figure 20. 34671 Functional Internal Block Diagram
INTEGRATED SUPPLY
CURRENT SETTING AND MONITOR
INTERNAL SUPPLY AND REFERENCE
This block programs the charge current in the constantcurrent mode and monitors the actual charge current during
the whole charge cycle.
This block steps down the high input voltage to a lower
voltage to power all the internal blocks. In addition, this block
generates the reference voltage for the charge control block.
SENSING AND CONTROL
VIN MONITOR
The input voltage monitor block monitors the input voltage
for two thresholds, power-on-reset (POR) and over-voltage
protection (OVP). If the input is lower than the POR or higher
than the OVP threshold, this block outputs a logic signal to
disable the charger.
CHARGE CONTROL
The charge-control block controls the gate voltage of the
power MOSFET to regulate the charge current, the battery
voltage, or the die temperature. It can also completely turn off
the power MOSFET to stop the current flow between the
input and the battery. Also, monitoring of the charge current
and the charger output voltage determines the trickle-charge
mode and the recharge cycle.
EOC (END OF CHARGE)
The EOC block monitors the charge current and the battery
voltage for the EOC conditions. Once the EOC conditions are
reached, this block outputs a logic signal to indicate the end
of the charge.
VIN-BAT COMPARATOR
The VIN-BAT comparator monitors the voltage difference
between the input voltage and the battery voltage. The input
voltage has to be higher than the battery voltage for the
charger to be enabled. If the input voltage falls below the
battery voltage, this block outputs a signal to disable the
charger to prevent the leakage current from the battery to the
input.
DIE TEMPERATURE FEEDBACK
The die temperature feedback block monitors the die
temperature. Once the die temperature reaches the
threshold temperature, the charge control block can reduce
the charge current to prevent further die temperature rise.
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Analog Integrated Circuit Device Data
Freescale Semiconductor
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
LOGIC
LOGIC CONTROL AND STATUS INDICATION
The logic control block determines the on and off of the
charger. It takes the signals from the VIN Monitor, VIN-BAT
Comparator, EOC, and the external enable signal, and
determines the on and off states as well as the charge status
indication outputs of the charger (CHG, PPR, and FAST).
POWER MOSFET
The power MOSFET passes the charging current from the
input to the output.
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Freescale Semiconductor
13
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
CHARGE CYCLE
outputs logic high voltage at the CHG pin to indicate that the
charging is completed.
The MC34671 uses the standard charge profile with
trickle, constant-current (CC), and constant-voltage (CV)
charge modes, as shown in Figure 21. Both the CC and the
CV charge modes are also called fast-charge mode. When
the input voltage rises above an internal power-on-reset
threshold, the PPR pin outputs a low voltage to indicate the
power supply presence. The charger starts with the tricklecharge mode until the battery voltage is above 2.7V. The
CHG pin outputs logic low voltage at the beginning of the
trickle-charge mode. If the battery voltage is unable to rise
due to a battery failure, charging will remain in the tricklecharge mode. When the battery voltage reaches the 2.7V
threshold, the MC34671 softly changes to the CC-mode. The
soft transition minimizes the input voltage drop and reduces
the requirement of the input decoupling capacitance. In the
fast-charge mode, the FAST pin outputs a low voltage. When
the battery voltage reaches 4.2V, the MC34671 enters the
CV-mode and regulates the output voltage at 4.2V. The
charge current decreases gradually in the CV-mode. When
the current drops to the EOC current threshold, the MC34671
Trickle
Constant Current
ITRKL
1. VIN > VOVP
2. VIN - VBAT < VOS
3. EN pin is high
where VOS is the offset voltage for the comparator that
monitors the input and the battery voltages.
Figure 22 shows the complete charge-cycle state
diagram.
ILOAD
>ICHG
Constant Voltage
4.2V
ICHG
2.7V
After the charging is completed, the MC34671 continues to
regulate the output to 4.2V, and monitors the output voltage.
If a load is in parallel with the battery, the charger continues
to output the current to the load even the charge is
completed. If the load current exceeds the programmed CCmode current, the battery will supply the additional current to
the load and the battery voltage will decline. Once the battery
voltage drops below the recharge voltage threshold, the
MC34671 returns to the fast-charge mode and indicates a
low voltage at the CHG pin.
When one of the following three conditions happens, the
MC34671 is disabled.
Charge
Voltage
100mV
Charge
Current
IEOC
TIME
CHG
TIME
FAST
TIME
Figure 21. Charge Profile
CHARGE CURRENT SETTING
An external resistor between the ISET pin and the ground
programmes the CC-mode current with the following
equation:
2667
I CHG = --------------------------R ISET + 96
equ. 2
where RISET is the resistor between the ISET pin and ground
in Ω. In addition, the current out of the ISET pin is proportional
to the charge current. The system may measure the ISET pin
34671
14
Analog Integrated Circuit Device Data
Freescale Semiconductor
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
voltage to monitor the actual charge current as given in
equ. 1 during the whole charging cycle.
EN pin is driven to a high logic voltage, the charger is
disabled.
CHARGE CURRENT LIMITATION
INPUT POWER PRESENCE INDICATOR
The charge current is limited by multiple factors.
When the voltage difference between the input and the
battery (VIN - VBAT) is low, (VIN - VBAT) / RDS(ON), where
RDS(ON) is the on resistance of the power MOSFET, may be
less than the programmed CC-mode current ICHG. The
charge current is limited by (VIN - VBAT) / RDS(ON) in this case.
When the voltage difference between the input and the
battery is too high, the large power dissipation may lead to
the charge current thermal foldback operation, due to the die
temperature regulation. The charge current is reduced to
prevent further temperature rise (See Charge Current
Thermal Foldback for more information).
When VIN is applied and the voltage is above the poweron-reset voltage threshold (VPOR), the PPR pin outputs a low
voltage to indicate the input power presence. The PPR output
is only controlled by the input voltage. All other functions,
such as the EN pin, the over-voltage protection, and the VINBAT comparator, do not affect the PPR output. The PPR pin
is capable to sink at least 12.0mA of current when outputting
a low voltage to drive an external LED.
DC INPUT VOLTAGE
The MC34671 accepts up to 28V DC input. When all of the
following conditions are satisfied, the input is in a power-good
range for the charger to start charging. The conditions
include:
1. VIN > VPOR
2. VIN - VBAT > VOS
3. VIN < VOVP
where VOS is the offset voltage for the comparator that
monitors the input and the battery voltages. The VOS is for
preventing the reverse leakage current from the battery when
the power supply is off. VOVP is the over-voltage protection
threshold. When the DC input voltage is above the overvoltage protection threshold, the charger is disabled
internally. The 28V input voltage rating eliminates the need of
any additional input over-voltage protection circuitry.
CHARGE-ENABLE INPUT
The charge-enable input, EN, has a weak internal pulldown current. Driving it to a low logic voltage, leaving it
floating, or shorting it to the ground, will enable the charger if
the input voltage is in the power-good range. Whenever the
CHARGE STATUS INDICATORS
The MC34671 has two charge status indicators, CHG and
FAST. CHG outputs a low voltage when the charger is
enabled and the charging is in progress. When the charge
cycle completes, CHG outputs high-impedance. If the
charger is disabled or the input voltage is out of the powergood range, the CHG pin outputs high-impedance as well.
The CHG pin has at least 12.0mA of current-sinking
capability to drive an external LED, same as the PPR pin.
FAST indicates whether the MC34671 is in the fast-charge
mode or not. When the charger is on and the battery voltage
is higher than the trickle-mode threshold, the charger enters
the fast-charge mode and FAST outputs a low voltage. The
open-drain FAST pin requires a pull-up resistor to output the
logic signal. If the charger is in the trickle-charge mode or is
disabled, or when the input voltage is out of the power-good
range, the FAST pin outputs high-impedance.
CHARGE CURRENT THERMAL FOLDBACK
An internal thermal feedback loop begins to reduce the
charge current when the die temperature reaches 110°C to
prevent further temperature rise. This feature protects the
MC34671 from over-temperature failures and allows the user
to push the limits of the power handling capability of a given
circuit board without the risk of damaging the MC34671. The
charge current can be programmed according to the typical
(not the worst-case) ambient temperature with the assurance
that the charger will automatically reduce the current in worstcase conditions.
34671
Analog Integrated Circuit Device Data
Freescale Semiconductor
15
FUNCTIONAL DEVICE OPERATION
STATE DIAGRAM
STATE DIAGRAM
PWR OFF
VINVPOR
EN=high
or VIN>VOVP
or VIN 2.7V
Charger: ON
VBAT < 2.7V
FAST CHARGE
Charger: ON
VBAT=4.2V
and IBAT < IEOC
VBAT
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