CN3791 [CONSONANCE]
Standalone Li-ion Battery Charger IC Photovoltaic Cell MPPT Function;
| 型号： | CN3791 |
| 厂家： | 
Shanghai Consonance Electronics Incorporated |
| 描述： | Standalone Li-ion Battery Charger IC Photovoltaic Cell MPPT Function 电池 |
| 文件： | 总11页 (文件大小：224K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
CONSONANCE
4A, Standalone Li-ion Battery Charger IC
With Photovoltaic Cell MPPT Function
CN3791
General Descriptions:
Features:
The CN3791 is a PWM switch-mode lithium ion
battery charger controller that can be powered by
photovoltaic cell with maximum power point
tracking function with few external components.
The CN3791 is specially designed for charging
lithium ion batteries with constant current and
constant voltage mode. In constant voltage mode,
the regulation voltage can be fixed at 4.2V with ±
1% accuracy. The constant charge current is
programmable with a single current sense resistor.
Deeply discharged batteries are automatically
trickle charged at 17.5% of the full-scale current
until the cell voltage exceeds 66.5% of constant
voltage. The charge cycle is terminated once the
charge current drops to 16% of full-scale current,
and a new charge cycle automatically restarts if the
battery voltage falls below 95.5% of regulation
voltage. CN3791 will automatically enter sleep
mode when input voltage is lower than battery
voltage.
Photovoltaic Cell Maximum Power Point
Tracking
Wide Input Voltage: 4.5V to 28V
Complete Charge Controller for single
cell Lithium-ion Battery
Charge Current Up to 4A
High PWM Switching Frequency:
300KHz
Constant Voltage: 4.2V±1%
Charging Current is programmed with a
current sense resistor
Automatic Conditioning of Deeply
Discharged Batteries
Automatic Recharge
Charging Status Indication
Soft Start
Battery Overvoltage Protection
Operating Ambient Temperature
－40℃to ＋85℃
Available in 10 Pin SSOP Package
Pb-free, Rohs-Compliant, Halogen Free
Other features include under voltage lockout,
battery over voltage protection, status indication.
CN3791 is available in a space-saving 10-pin
SSOP package.
Pin Assignment:
VG
10
9
DRV
VCC
1
Applications:
GND
2
CN3791
Power Bank
CSP
CHRG
DONE
8
3
4
5
Hand-held Equipment
BAT
7
Battery-Backup Systems
Portable Industrial and Medical Equipment
Standalone Battery Chargers
MPPT
6
COM
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Typical Application Circuit:
D1
RCS
L
Input Supply
M1
*
C2
100nF
C1
BAT
C3
D2
10
1
VG
DRV
9
VCC
8
7
R3
R1
CSP
BAT
CN3791
D3
D4
5
3
COM
CHRG
4
6
R2
120
DONE
MPPT
GND
C4
220nF
2
R4
*: D1 can be omitted, refer to section ꢀDiode Selectionꢁon Page 9
Figure 1 Typical Application Circuit
Ordering Information:
Part No.
CN3791
Shipment
Tape and Reel, 3000/Reel
Operating Ambient Temperature
－40℃to ＋85℃
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Pin Description:
Pin No.
Name
Descriptions
Internal Voltage Regulator. VG internally supplies power to gate driver,
connect a 100nF capacitor between VG pin and VCC pin.
1
2
3
VG
GND
Ground. Negative terminal of input supply.
Open-Drain Charge Status Output. When the battery is being charged, this pin
is pulled low by an internal switch. Otherwise this pin is in high impedance state.
Open-Drain Charge Termination Output. When the charging is terminated,
this pin is pulled low by an internal switch. Otherwise this pin is in high
impedance state.
4
5
6
Loop Compensation Input. Connect a 220nF capacitor in series with an 120Ω
resistor from this pin to GND.
COM
Photovoltaic Cell Maximum Power Point Tracking Pin. Connect this pin to
the external resistor divider for maximum power point tracking. In maximum
power point tracking status, the MPPT pin’s voltage is regulated to 1.205V.
Negative Input for Charge Current Sensing. This pin and the CSP pin measure
the voltage drop across the sense resistor RCS to provide the current signals
required.
MPPT
7
8
BAT
CSP
Positive Input for Charge Current Sensing. This pin and the BAT pin measure
the voltage drop across the sense resistor RCS to provide the current signals
required.
External DC Power Supply Input. VCC is also the power supply for internal
circuit. Bypass this pin with capacitors.
9
VCC
DRV
10
Gate Drive Pin. Drive the gate of external P-channel MOSFET.
Absolute Maximum Ratings
Voltage from VCC, VG, DRV, CHRG, DONE to GND…….…－0.3V to 30V
Voltage from VG to VCC………………………………………－8V to VCC＋0.3V
Voltage from CSP, BAT, COM, MPPT to GND………….……－0.3V to 6.5V
Storage Temperature………………………………………...…－65℃to 150℃
Operating Ambient Temperature………………………….……－40℃to 85℃
Lead Temperature(Soldering, 10 seconds)………………..……260℃
Stresses beyond those listed under ‘Absolute Maximum Ratings’ may cause permanent damage to the device. These are stress
ratings only and functional operation of the device at these or any other conditions above those indicated in the operational
sections of the specifications is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect
device reliability.
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Electrical Characteristics:
(VCCꢂ15V, TAꢂ－40℃to 85℃, unless otherwise noted)
Parameters
Input Voltage Range
Under voltage lockout
Threshold
Symbol
Conditions
Min
Typ
Max
28
Unit
VCC
4.5
V
VUVLO
3.1
3.8
4.4
V
Operating Current
Regulation Voltage
IVCC
No switching
0.7
1.0
4.2
1.3
4.247
130
36
mA
V
VREG
Constant voltage mode
VBATꢃVPRE, VCSP－VBAT
VBATꢄVPRE, VCSP－VBAT
Termination, VBATꢂ3.7V
Sleep mode, VBATꢂ3.7V
VBAT rises
4.158
110
10
120
Current Sense
VCS
mV
uA
21
10
IBAT1
IBAT2
VPRE
15
Current into BAT Pin
Precharge Threshold
15
64
66.5
2.5
69 %VREG
Precharge
Hysteresis
Charge
Threshold
VBAT falls
%VREG
HPRE
Iterm
Termination
Charge current decreases
16
%ICC
Threshold
Recharge Threshold
Overvoltage Trip Level
Overvoltage Clear Level
MPPT Pin
VRE
Vov
Vclr
VBAT falls
VBAT rises
VBAT falls
95.5
1.07
1.02
%VREG
1.04
1.0
1.1
VREG
1.04
MPPT Regulation Voltage
MPPT Pin Bias Current
CHRG Pin
VMPPT
IMPPT
Maximum power point track 1.18
－100
1.205
0
1.23
V
＋100
nA
7
12
18
1
mA
uA
Pin Sink Current
V
CHRGꢂ1V, charge mode
CHRGꢂ25V,termination
ICHRG
ILK1
V
Leakage Current
DONE Pin
mode
V
DONEꢂ1V, termination
7
12
18
1
mA
uA
Sink Current
IDONE
ILK2
mode
VDONEꢂ25V, charge mode
Leakage Current
Oscillator
Switching Frequency
Maximum Duty Cycle
Sleep Mode
240
300
94
360
kHZ
%
fosc
Dmax
VCC falling, VBATꢂ3.7V,
measure VCC－VBAT
Sleep Mode Threshold
0.0
0.02
0.32
0.1
V
V
VSLP
Sleep mode Release
Threshold
VCC rising, VBATꢂ3.7V,
measure VCC－VBAT
0.26
0.39
VSLPR
Note: VREG is the regulated voltage in constant voltage mode; ICC is the charge current in constant current mode.
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Electrical Characteristics: (Continued)
Parameters
DRV Pin
VDRV High (VCC－VDRV
Symbol
Conditions
Min
Typ
Max
Unit
)
VH
VL
tr
IDRVꢂ－10mA
60
6.3
40
40
mV
V
VDRV Low (VCC－VDRV
)
IDRVꢂ0mA
Rise Time
Cloadꢂ2nF, 10% to 90%
Cloadꢂ2nF, 90% to 10%
30
30
65
65
Ns
Ns
Fall Time
tf
Detailed Description:
The CN3791 is a constant current, constant voltage Li-Ion battery charger controller that can be powered by the
photovoltaic cell with maximum power point tracking function, the device adopts PWM step-down (buck)
switching architecture. The charge current is set by an external sense resistor (RCS) across the CSP and BAT pins.
The final battery regulation voltage in constant voltage mode is set at 4.2V typical with 1% accuracy.
A charge cycle begins when the voltage at the VCC pin rises above VUVLO and the battery voltage by VSLPR, and
the voltage at MPPT pin is greater than 1.23V. At the beginning of the charge cycle, if the battery voltage is less
than 66.5% of regulation voltage (VREG), the charger goes into trickle charge mode. The trickle charge current is
internally set to 17.5%(Typical) of the full-scale current. When the battery voltage exceeds 66.5% of regulation
voltage, the charger goes into the full-scale constant current charge mode. In constant current mode, the charge
current is set by the external sense resistor RCS and an internal 120mV reference, the charge current equals to
120mV/RCS. When the battery voltage approaches the regulation voltage, the charger goes into constant voltage
mode, and the charge current will start to decrease. When the charge current drops to 16% of the full-scale
current, the charge cycle is terminated, the DRV pin is pulled up to VCC, and an internal comparator turns off
the internal pull-down N-channel MOSFET at the
pin, another internal pull-down N-channel MOSFET at
the pin is turned on to indicate the termination status.
To restart the charge cycle, just remove and reapply the input voltage. Also, a new charge cycle will begin if the
battery voltage drops below the recharge threshold voltage of 95.5% of the regulation voltage.
The CN3791 adopts the constant voltage method to track the photovoltaic cell’s maximum power point. The
MPPT pin’s voltage is regulated to 1.205V to track the maximum power point of the solar panel.
When the input voltage is not present, the charger automatically goes into sleep mode, all the internal circuits are
shutdown.
An overvoltage comparator guards against voltage transient overshoots (>7% of regulation voltage). In this case,
P-channel MOSFET are turned off until the overvoltage condition is cleared. This feature is useful for battery
load dump or sudden removal of battery.
The charging profile is shown in Figure 2.
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Precharge
Phase
Constant Current
Constant Voltage
Phase
Phase
4.2V/cell
2.8V/cell
Charge terminated
Charge Current
Battery Voltage
Figure 2 The Charging Profile(FB pin is connected to BAT pin)
Application Information
Under voltage Lockout (UVLO)
An under voltage lockout circuit monitors the input voltage and keeps the charger off if VCC falls below
3.8V(Typical).
Trickle Charge Mode
At the beginning of a charge cycle, if the battery voltage is below 66.5% of the regulation voltage, the charger
goes into trickle charge mode with the charge current reduced to 17.5% of the full-scale current.
Charge Current Setting
The full-scale charge current, namely the charge current in constant current mode, is decided by the following
formula:
Where:
ICH is the full scale charge current
RCS is the resistor between the CSP pin and BAT pin
The Maximum Power Point Tracking
CN3791 adopts the constant voltage method to track the photovoltaic cell’s maximum power point. From I-V
curve of photovoltaic cell, under a given temperature, the photovoltaic cell’s voltages at the maximum power
point are nearly constant regardless of the different irradiances. So the maximum power point can be tracked if
the photovoltaic cell’s output voltage is regulated to a constant voltage.
CN3791’s MPPT pin’s voltage is regulated to 1.205V to track the maximum power point working with the
off-chip resistor divider(R3 and R4 in Figure 1).
The maximum power point voltage is decided by the following equation:
V
MPPTꢂ1.205×(1＋R3／R4)
Charge Termination
In constant voltage mode, the charge current decreases gradually. When the charge current decreases to 16% of
the full-scale current, the charging is terminated, the external P-channel MOSFET is turned off, no charge
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current is delivered to battery any more.
Automatic Recharge
After the charge cycle is completed and both the battery and the input power supply (wall adapter) are still
present, a new charge cycle will begin if the battery voltage drops below 95.5% of the regulation voltage due to
self-discharge or external loading. This will keep the battery capacity at more than 80% at all times without
manually restarting the charge cycle.
Status Indication
The CN3791 has 2 open-drain status outputs:
and
.
pin is pulled low when the charger is in
pin is pulled low if the charger is in charge
charging status, otherwise
becomes high impedance.
becomes high impedance.
termination status, otherwise
When the battery is not present, the charger charges the output capacitor to the regulation voltage quickly, then
the BAT pin’s voltage decays slowly to recharge threshold because of low leakage current at BAT pin, which
results in a ripple waveform at BAT pin, in the meantime,
absence.
pin outputs pulse to indicate the battery’s
The open drain status output that is not used should be tied to ground.
The table 1 lists the two indicator status and its corresponding charging status. It is supposed that red LED is
connected to
pin and green LED is connected to
pin.
State Description
Charging
pin
pin
Low(the red LED on)
High Impedance(the green LED off)
Low(the green LED on)
High Impedance(the red LED off)
Pulse (the red LED blinking)
Charge termination
Battery not present
There are 2 possible reasons:
Pulse (the green LED on or blinking)
the voltage at the VCC pin
below the UVLO level or
the voltage at the VCC pin
below VBAT
High Impedance(the red LED off)
High Impedance(the green LED off)
Table 1 Indication Status
Gate Drive
The CN3791’s gate driver can provide high transient currents to drive the external pass transistor. The rise and
fall times are typically 40ns when driving a 2000pF load, which is typical for a P-channel MOSFET with Rds(on)
in the range of 30mΩ.
A voltage clamp is added to limit the gate drive to 8V max. below VCC. For example, if VCC is 20V, then the
DRV pin output will be pulled down to 12V min. This allows low voltage P-channel MOSFETs with superior
Rds(on) to be used as the pass transistor thus increasing efficiency.
Loop Compensation
In order to make sure that the current loop and the voltage loop are stable, a series-connected 220nF ceramic
capacitor and 120Ω resistor from the COM pin to GND are necessary.
Battery Detection
CN3791 does not provide battery detection function, when the battery is not present, the charger charges the
output capacitor to the regulation voltage quickly, then the BAT pin’s voltage decays slowly to recharge
threshold because of low leakage current at BAT pin, which results in a ripple waveform at BAT pin, in the
meantime,
pin outputs pulse to indicate the battery’s absence.
It is generally not a good practice to connect a battery while the charger is running, otherwise the charger may be
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in uncertain state, or deliver a large surge current into the battery for a brief time.
Input Capacitors
Since the input capacitor(C1 in Figure 1) is assumed to absorb all input switching ripple current in the converter,
it must have an adequate ripple current rating. Worst-case RMS ripple current is approximately one-half of
output charge current.
In order to depress the high-frequency oscillation during P-channel MOSFET’s turning on and off, it is best that
the input capacitor consists of the following 3 capacitors in parallel:
Electrolytic capacitor for low-frequency filtering
A ceramic capacitor from 1uF to 10uF
A high-frequency capacitor from 47nF to 1uF
Output Capacitors
The selection of output capacitor (C3 in Figure 1) is primarily determined by the ESR required to minimize
ripple voltage and load step transients. it is best that the input capacitor consists of the following 2 capacitors in
parallel:
A 10uF electrolytic capacitor for low-frequency filtering
A ceramic capacitor from 1uF to 10uF
If only ceramic capacitor can be used, cares must be taken that some ceramic capacitors exhibit large voltage
coefficient, which may lead to high voltage at BAT pin when battery is not present. In this case, the capacitor
value should be increased properly so that no damage will be done.
Inductor Selection
During P-channel MOSFET’s on time, the inductor current increases, and decreases during P-channel
MOSFET’s off time, the inductor’s ripple current increases with lower inductance and higher input voltage.
Higher inductor ripple current results in higher charge current ripple and greater core losses. So the inductor’s
ripple current should be limited within a reasonable range.
The inductor’s ripple current is given by the following formula:
Where,
f is the switching frequency 300KHz
L is the inductor value
VBAT is the battery voltage
VCC is the input voltage
A reasonable starting point for setting inductor ripple current is △ILꢂ0.3×ICH, ICH is the charge current.
Remember that the maximum △IL occurs at the maximum input voltage and the lowest inductor value. So
lower charge current generally calls for larger inductor value.
In the meantime, inductor value should meet the requirement of the following equation:
MOSFET Selection
The CN3791 uses a P-channel power MOSFET switch. The MOSFET must be selected to meet the efficiency or
power dissipation requirements of the charging circuit as well as the maximum temperature of the MOSFET.
The peak-to-peak gate drive voltage is set internally, this voltage is typically 6.3V. Consequently, logic-level
threshold MOSFETs must be used. Pay close attention to the BVDSS specification for the MOSFET as well;
many of the logic-level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFET includes the “on” resistance Rds(on), total gate charge Qg, reverse
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transfer capacitance CRSS, input voltage and maximum current.
The MOSFET power dissipation at maximum output current is approximated by the equation:
Where:
Pd is the power dissipation of the power MOSFET
VBAT is the maximum battery voltage
VCC is the minimum input voltage
Rds(on) is the power MOSFET’s on resistance at room temperature
ICH is the charge current
dT is the temperature difference between actual ambient temperature and room temperature(25℃)
In addition to the I2Rds(on) loss, the power MOSFET still has transition loss, which are highest at the highest
input voltage. Generally speaking, for VINꢄ20V, the I2Rds(on) loss may be dominant, so the MOSFET with
lower Rds(on) should be selected for better efficiency; for VINꢃ20V, the transition loss may be dominant, so
the MOSFET with lower CRSS can provide better efficiency. CRSS is usually specified in the MOSFET
characteristics; if not, then CRSS can be calculated using CRSS = QGD/ΔVDS.
The MOSFETs such as CN2305, 4459, 4435, 9435, 3407A can be used. The part numbers listed above are for
reference only, the users can select the right MOSFET based on their requirements.
Diode Selection
The diodes D1 and D2 in Figure 1 are schottky diode, the current rating of the diodes should be at least the
charge current limit, the voltage rating of the diode should exceed the maximum expected input voltage.
The diode that is much larger than that is sufficient can result in larger transition losses due to their larger
junction capacitance.
Diode D1 in Figure 1 is used as block diode to prevent battery current from flowing back to VCC when input
supply is absent. Even without D1, CN3791 consumes only about 30uA current from battery(VBATꢂ4.2V), so
diode D1 can be removed if the 30uA battery current is not a consideration.
Battery Current In Sleep Mode
In the typical application circuit shown in Figure 1, when input voltage is powered off or lower than battery
voltage, CN3791 will enter sleep mode. In sleep mode, the battery current includes:
(1) The current into BAT pin and CSP pin, which is about 9uA(VBATꢂ4.2V).
(2) The current from battery to VCC pin via diode D1, which is determined by D1’s leakage current. If diode
D1 is not used, then the current flowing to VCC pin via inductor and body diode of P-channel MOSFET is
about 21uA(VBATꢂ4.2V).
(3) The current from battery to GND via diode D2, which is also determined by D2’s leakage current.
PCB Layout Considerations
When laying out the printed circuit board, the following considerations should be taken to ensure proper
operation of the IC.
(1) To minimize radiation, the 2 diodes, pass transistor, inductor and the input bypass capacitor traces should be
kept as short as possible. The positive side of the input capacitor should be close to the source of the
P-channel MOSFET; it provides the AC current to the pass transistor. The connection between the diode and
the pass transistor should also be kept as short as possible.
(2) The compensation capacitor connected at the COM pin should return to the ground pin of the IC. This will
prevent ground noise from disrupting the loop stability.
(3) Output capacitor ground and catch diode (D2 in Figure 1) ground connections need to feed into same copper
that connects to the input capacitor ground before tying back into system ground.
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(4) Analog ground and power ground(or switching ground) should return to system ground separately.
(5) The ground pins also works as a heat sink, therefore use a generous amount of copper around the ground
pins. This is especially important for high VCC and/or high gate capacitance applications.
(6) Place the charge current sense resistor RCS right next to the inductor output but oriented such that the IC’s
CSP and BAT traces going to RCS are not long. The 2 traces need to be routed together as a single pair on the
same layer at any given time with smallest trace spacing possible.
(7) The CSP and BAT pins should be connected directly to the 2 terminals of current sense resistor (Kelvin
sensing) for best charge current accuracy. See Figure 3 as an example.
Figure 3 Kelvin Sensing of Charge Current
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Package Information
Consonance does not assume any responsibility for use of any circuitry described. Consonance reserves the
right to change the circuitry and specifications without notice at any time.
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