NCP1835B ON Semiconductor, NCP1835B Datasheet - Page 11

• Manufacturer Part Number: NCP1835B
• Description: Integrated Li-Ion Charger
• Manufacturer: ON Semiconductor

Input and Output Capacitor Selection
recommended for the input bypass capacitor. For the output
capacitor, when there is no battery inserted and the
NCP1835B is used as an LDO with 4.2 V or 4.242 V output
voltage, a 4.7 mF or higher value tantalum capacitor is
recommended for stability. With the battery attached, the
output capacitor can be any type with the value higher than
0.1 mF.
C
to prevent the battery from continuously charging which
can cause premature aging or safety issues. The timing
capacitor between TIMER pin and ground, C
end−of−charge time, TIMEOUT, and the pre−charge
timeout. This capacitor is required for proper device
operation.
discharges it to 0.6 V with 6 mA current in one period.
Therefore, the period of the oscillator is:
it reaches the maximum number corresponding to
end−of−charge time, TIMEOUT.
timeout signal if the battery has not completed charging
within the TIMEOUT period. The timeout signal then
forces the FAULT pin low.
C
operation.
Table 2. TIMEOUT vs. C
TIME
T OSC + 2
TIME
A 4.7 mF or higher value ceramic capacitor is
The NCP1835B offers an end−of−charge timeout timer
The internal oscillator charges C
A 22−binary counter counts every oscillator period until
The NCP1835B will terminate charging and give a
The following Table 2 shows the desired TIMEOUT vs.
TIMEOUT + 2
Selection for Programming Charge Time
sizes. The C
C
TIME
0.47
5.6
8.2
10
15
33
56
1
C TIME
(nF)
22
I C
TIME
T OSC + 14
dV c
TIME
is required for proper device
+ 0.2
Size
TIMEOUT (minute)
TIME
10
C TIME
6
1 nF
to 1.2 V and then
115
140
210
462
784
6.6
14
78
C TIME (sec)
APPLICATION INFORMATION
TIME
(minute)
, sets the
(eq. 1)
(eq. 2)
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NCP1835B
11
Thermal Considerations
3x3 mm DFN package. In order to deliver the maximum
power dissipation under all conditions, it is very important
that the user solders exposed metal pad under the package
to the ground copper area and then connect this area to a
ground plane through thermal vias. This can greatly reduce
the thermal impedance of the device and further enhance
its power dissipation capability and thus its output current
capability.
Charging with Constant Voltage Adapters or Current
Limited Adapters
regulated adapters: a traditional constant voltage type or a
current limited type. Figure 16 illustrates the operation of
the linear charger powered with a standard constant voltage
adapter. The power dissipation in the linear charger is:
beginning of a full current charge, since this is the point that
the power supply and the battery voltage have the largest
difference. As the battery voltage rises during charging, the
power dissipation drops. After entering the constant
voltage mode, the power dissipation drops further due to
the decreasing charge current. The maximum power that
the linear charger can dissipate is dependent on the thermal
resistance of the device. In case the device can not handle
the maximum power P1, the thermal foldback loop reduces
the charge current which limits the power dissipation to the
sustained level P2. Figure 16 shows this.
thermal performance than the above example. A current
limited adapter operates as a constant voltage adapter
before the charge current reaches the current limit. I
must be less than the programmed full charge current
I
source the current limit I
drop to follow the battery voltage. If the application uses
the adapter to power its systems while the battery is being
charged, this drooping voltage can be an issue.
adapter occurs at the beginning of the constant voltage
mode, which is shown at point P3 in Figure 17. If P3 is
higher than P2, the maximum power dissipation that the
charger can handle, then the thermal foldback function will
be activated.
FCHG
The NCP1835B is housed in a thermally enhanced
The NCP1835B can be powered from two types of
The maximum power dissipation P1 happens at the
Using the adapter’s current limit can provide better
The worst case power dissipation with a current limited
. Once the current limit is reached, the adapter will
P dis + (V CC * V BAT)
LIM
while its output voltage will
I CHG
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(eq. 3)
LIM