CONSONANCE

4A, Multi-Chemistry Battery Charger

With Photovoltaic Cell MPPT Function
CN3795
General Descriptions: Features:
The CN3795 is a PWM switch-mode  Photovoltaic Cell Maximum Power Point
multi-chemistry battery charger controller that can Tracking
be powered by photovoltaic cell with maximum  Wide Input Voltage: 6.6V to 30V
power point tracking function using few external  Complete Charge Controller for Single-
components. or Multi-cell Lithium ion, LiFePO4 or
The CN3795 is specially designed for charging Lithium Titanate Batteries
lithium ion，LiFePO4 or Lithium Titanate batteries  Charge Current Up to 4A
with constant current and constant voltage mode.  PWM Switching Frequency: 310KHz
In constant voltage mode, the regulation voltage is  Can be used as Voltage Source when
set by 2 external resistors. The constant charging Battery is Absent
current is programmable with a single current sense  Charging Current is programmed with a
resistor. current sense resistor
Deeply discharged batteries are automatically  Automatic Conditioning of Deeply
trickle charged at 17.5% of the programmed Discharged Batteries
constant charging current until the cell voltage  Automatic Recharge
exceeds 66.5% of constant voltage. The charge  Charging Status Indication
cycle is terminated once the charging current drops  Soft Start
to 16% of full-scale current, and a new charge  Battery Overvoltage Protection
cycle automatically restarts if the charge current  Operating Ambient Temperature
rises above 58.8% of full-scale charge current. －40℃ to ＋85℃
CN3795 will automatically enter sleep mode when  Available in 10-Pin SSOP Package
input voltage is lower than battery voltage.  Pb-free, Rohs-Compliant, Halogen Free
Other features include under voltage lockout,
battery over voltage protection, status indication,
Pin Assignment:
etc.
CN3795 is available in a space-saving 10-pin VG 1 10 DRV
SSOP package. GND 2 9 VCC
CHRG 3 CN3795 8 CSP
Applications:
MPPT 4 7 BAT
 Hand-held Equipment COM 5 6 FB
 Emergency Lamp and Camping Lamp
 Battery-Backup Systems
 Portable Industrial and Medical Equipment
 Standalone Chargers for Lithium ion,
LiFePO4 or Lithium Titanate Batteries

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Typical Application Circuit:

D1
Input Supply M1 L RCS
*
C2
C1 100nF
C3
D2 BAT

1 10
VG DRV
9
VCC
8
R3 CSP

BAT 7
CN3795
R5 D3 FB 6
R1
COM 5
3 CHRG
R4
4 MPPT 120
R2
GND
R6 C4
2
220nF

*: Diode D1 can be omitted, refer to section “Diode Selection”

on Page 9.

Figure 1 Typical Application Circuit

Ordering Information:

Part No. Shipment Operating Ambient Temperature

CN3795 Tape and Reel, 3000/Reel －40℃ to ＋85℃

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Pin Description:
Pin No. Name Descriptions
Internal Voltage Regulator. VG internally supplies power to gate driver,
1 VG
connect a 100nF capacitor between VG pin and VCC pin.
2 GND Ground. Negative terminal of input supply.
Open-Drain Charge Status Output. When the battery is being charged, this pin
3
is pulled low by an internal switch. Otherwise this pin is in high impedance state.
Photovoltaic Cell Maximum Power Point Tracking Pin. Connect this pin to
4 MPPT 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.
Loop Compensation Input. Connect a 220nF capacitor in series with an 120Ω
5 COM
resistor from this pin to GND.
Battery Voltage Feedback Input. Generally this Pin is connected to the external
6 FB
feedback resistor divider to sense the battery voltage.
Negative Input for Charge Current Sensing. This pin and the CSP pin measure
7 BAT the voltage drop across the sense resistor RCS to provide the current signals
required.
Positive Input for Charge Current Sensing. This pin and the BAT pin measure
8 CSP 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
9 VCC
circuit. Bypass this pin with capacitors.
10 DRV Gate Drive Pin. Drive the gate of external P-channel MOSFET.

Absolute Maximum Ratings

Voltage from VCC, CHRG to GND………………………....………….……...…－0.3V to 33V
Voltage from VG, DRV to VCC…………………………………...…..……－8V to VCC＋0.3V
Voltage from CSP, BAT to GND………..…………………………………………－0.3V to 25V
Voltage from MPPT, COM, FB 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:
(VCC＝15V, TA＝－40℃ to 85℃, unless otherwise noted)
Parameters Symbol Conditions Min Typ Max Unit
Input Voltage Range VCC 6.6 30 V
Under voltage lockout
UVLO 4 5.2 6.5 V
Threshold
Operating Current IVCC No switching 0.7 1.0 1.3 mA
FB Pin Feedback Voltage VFB Constant voltage mode 1.193 1.205 1.22 V
FB pin Bias Current IFB VFB＝1.2V 60 300 nA
VBAT＞VPRE, VCSP－VBAT 110 120 130
Current Sense VCS mV
VBAT＜VPRE, VCSP－VBAT 10 21 36
IBAT1 Termination, VBAT＝7.4V 10 15
Current into BAT Pin uA
IBAT2 Sleep mode, VBAT＝7.4V 15
Precharge Threshold VPRE VBAT rises 64 66.5 69 %VREG
Precharge Threshold
HPRE VBAT falls 2.5 %VREG
Hysteresis
Charge Termination
Iterm Charge current decreases 16 %ICC
Threshold
Recharge Threshold VRE Charge Current Rises 58.8 %ICC
Overvoltage Trip Level Vov VBAT rises 1.04 1.07 1.1
VREG
Overvoltage Clear Level Vclr VBAT falls 1.0 1.02 1.04
CHRG Pin
Pin Sink Current ICHRG VCHRG＝1V, charge mode 7 12 18 mA
Leakage Current ILK1 VCHRG＝25V,termination mode 1 uA
MPPT Pin
MPPT Regulation Voltage VMPPT Maximum power point track 1.18 1.205 1.23 V
MPPT Pin Bias Current IMPPT －100 0 ＋100 nA
Oscillator
Switching Frequency fosc 260 310 360 kHZ
Maximum Duty Cycle Dmax 94 %
Sleep Mode
Sleep Mode Threshold
VSLP VCC falling VBAT＝8V 0.0 0.05 0.1 V
(measure VCC－VBAT)
Sleep mode Release
Threshold VSLPR VCC rising, VBAT＝8V 0.2 0.32 0.46 V
(measure VCC－VBAT)
DRV Pin
VDRV High (VCC－VDRV) VH IDRV＝－10mA 60 mV
VDRV Low (VCC－VDRV) VL IDRV＝0mA 6.3 V
Rise Time tr Cload＝2nF, 10% to 90% 30 40 65 ns
Fall Time tf Cload＝2nF, 90% to 10% 30 40 65 ns
Note: VREG is the regulated voltage in constant voltage mode; ICC is the charge current in constant current mode.

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Detailed Description:
The CN3795 is a constant current, constant voltage battery charger controller that can be powered by the
photovoltaic cell with maximum power point tracking function. The CN3795 adopts PWM step-down (buck)
switching architecture, and can be used to charge single- or multi-cell Lithium ion battery, LiFePO4 or Lithium
Titanate batteries. 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 can be set by 2 feedback resistors at FB pin.
A charge cycle begins when the voltage at the VCC pin rises above the UVLO level and is greater than the
battery voltage by VSLPR. 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, an internal comparator turns off the internal pull-down N-channel MOSFET at the
pin 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
charge current rises above the recharge threshold of 58.8% of the full-scale charge current.
The CN3795 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 photovoltaic cell.
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,
the external 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.

Precharge Constant Current Constant Voltage

Phase Phase Phase

Vreg

Vpre

Charge terminated

Charge Current
Battery Voltage

Figure 2 The Charging Profile

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Application Information
Under voltage Lockout (UVLO)
An under voltage lockout circuit monitors the input voltage and keeps the charger off if VCC falls below
6.5V(Maximum).
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
Set the Regulation Voltage
As shown in Figure 1, battery voltage is feedback to FB pin via the resistor divider composed of R1 and R2.
CN3795 decided the charging status based on FB’s voltage. When FB’s voltage approaches 1.205V, the charger
goes into constant voltage mode. In constant voltage mode, the charge current decrease gradually, and the battery
voltage remains unchanged.
In light of FB pin’s bias current, the regulation voltage in constant voltage mode is determined by the following
equation:
VREG＝1.205×(1＋R1／R2)＋IB×R1
Where, IB is FB pin’s bias current, which is 60nA typical.
From the above equation, we can see that an error is introduced due to the existence of bias current IB, the error
is IB×R1. If R1＝500KΩ, then the error is about 30mV. So the error should be taken into account while
designing the resistor divider.
The maximum regulation voltage that can be set is 25V.
The Maximum Power Point Tracking
CN3795 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.
CN3795’s MPPT pin’s voltage is regulated to 1.205V to track the maximum power point working with the
off-chip resistor divider(R5 and R6 in Figure 1).
The maximum power point voltage is decided by the following equation:
VMPPT＝1.205×(1＋R5／R6)
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. In charge termination mode, pin outputs high
impedance to indicate the charge termination mode, and CN3795 will continue to charge the battery in constant
voltage mode to ensure that the battery is fully charged.
In photovoltaic cell’s maximum power point tracking mode, the charging will not be terminated until the battery
voltage is higher than 95.8% of the regulation voltage set by the feedback resistors at FB pin, even though the
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