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參數(shù)資料
| 型號： | LM3621 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Single Cell Lithium-Ion Battery Charger Controller |
| 中文描述： | 單節(jié)鋰離子電池充電控制器 |
| 文件頁數(shù)： | 11/14頁 |
| 文件大?。?/td> | 334K |
| 代理商： | LM3621 |
Application Information
(Continued)
Programmable Charge Termination Voltage
The charging status for battery of graphite or coke anode is
programmed with the digital input “V
”. V
= LO for a
charge termination voltage of 4.1V, a float voltage of 3.84V
and over voltage detection threshold (V
-Det) of 4.3V.
V
= HI for a charge termination voltage of 4.2V, float volt-
age of 4.09V and V
BAT
-Det of 4.4V.
Defective Pack Detection
The LM3621 automatically checks for defective battery.
Whenever a defective pack is detected, the charging se-
quence is suspended and LED1 driver is pulsed at a rate of
0.8 Hz. A defective battery is indicated under three condi-
tions: (1) when a battery fails to charge up to 2.55V within
one hour, (2) when the battery ESR plus the contact resis-
tance is excessive, and (3) when the pack is an open circuit.
Step by Step Description of a Typical Charging
Sequence. (Refer to
Figure 3
)
1. Standby Mode
The LM3621 will remain in standby while the digital inputs to
the Enable and Boost pins are low. Boost overrides Enable,
and Boost mode may be activated at any time with two ex-
ceptions: (1) when a deeply discharged battery (i.e., V
BAT-
TERY
≤
2.5V) is attached to the charger or (2) when ChgInt
has been activated during a normal charge cycle. Both LED
drivers pull low during Boost mode. During standby, the
charger’s output voltage V
is regulated to either 4.2V or
4.1V depending on the state of the digital input to the V
pin (V
= 4.2V when V
= high or V
= 4.1V when
V
= low). PFD is low so the low side pass FET is off. The
LED driver pins are high impedance (open drain). Table 1
shows the state of the LED drivers during various modes of
operation.
2. Charging Sequence Initialization
The LM3621 determines the presence or absence of a bat-
tery pack by the state of the “Enable” pin. Enable should be
pulled low when the pack is not present. When a pack is in-
serted into the charger, Enable should go high to initiate the
charging sequence.
After Enable is asserted with a battery connected to the
charger, LED1 goes low and there is a one-second delay be-
fore current is allowed to flow into the battery. During this de-
lay, the LM3621 checks the charge condition of the battery to
determine if it is grossly overcharged or if it is deeply dis-
charged. If the battery is grossly overcharged, PFD stays low
keeping the low side pass FET off, and both LED drivers
pulse at a frequency of 0.8 Hz to indicate a fault condition. If
the battery is less than 2.55V, the LM3621 goes to the Hi-Z
( battery conditioning) charge mode. During the Hi-Z charge
mode, V
is regulated to 4.1V, and the voltage (V
)
across the current sense resistor (R
) is regulated to 50
mV. The LM3621 is capable of charging a battery that has
been discharged down to as low as 0V. This is accomplished
by the fact that the “ON” resistance of the low side N-channel
pass FET is modulated by the PFD output. This ensures that
V
stays constant at 50 mV regardless of what the battery
voltage is, and it prevents the charger’s regulation loop from
collapsing in the event that the charger’s output is shorted.
The LM3621 will remain in the Hi-Z Charge mode for a maxi-
mum of one hour. If the battery voltage does not increase to
at least 2.55V by the end of the one-hour interval, then PFD
goes low to turn off the low side pass FET and LED1 will
pulse at 0.8 Hz to indicate a defective battery.
3. Fast Charge Mode
The LM3621 will transition to Fast Charge mode whenever
the battery voltage is above 2.55V. During Fast Charge
mode LED1 stays low and LED2 stays open drain, and the
LM3621 controls the charger to behave as a current limited,
constant output voltage source to the battery. If the battery
voltage is less than 4.2V (for V
= HI), the LM3621 con-
trols the charger to behave as a constant current source.
V
is limited to 0.5V, so the maximum charge current de-
livered to the battery is equal to 0.5V / R
. Once the battery
voltage reaches 4.2V, the LM3621 controls the charger to
behave as a constant voltage source, and V
is main-
tained at 4.2V. As the battery continues to charge up, the
charge current will decrease. Correspondingly, V
CSR
will de-
crease as well.
The battery will continue to charge until V
has decreased
to 40 mV, at which time PFD pulls low to interrupt the charge
current for one second.At the end of the one second interval,
the LM3621 checks to see if the battery’s Resistance Free
Voltage (RFV) is greater than 3.65V or less than 3.65V. If the
battery’s RFV is less than 3.65V, then the ESR of the battery
is excessively high, PFD stays low to keep the charging se-
quence suspended and LED1 pulses at 0.8 Hz to indicate a
defective battery. If the battery’s RFV is greater than 3.65V,
then the LM3621 transitions to Top-Off mode. At this transi-
tion, LED1 becomes open drain and LED2 pulls low indicat-
ing a fully charged battery.
4. Top-Off Mode
During Top-Off mode, the battery is trickle charged for one
hour. At the end of the one hour interval, PFD goes low to
terminate charging (i.e., the charge current is interrupted),
and the LM3621 transitions to Battery Monitor mode.
5. Monitor Mode
During Monitor mode, V
drops to 4.09V (if V
is high)
or 3.84V (if V
is low), and the battery is floating. The
LM3621 typically draws less than 1 μA from the battery dur-
ing Monitor mode. If the battery self discharges so that its
voltage decreases to 4.09V (if V
is high) or 3.84V (if V
is low), then the LM3621 will transition back to Fast Charge
mode to refresh the battery and charge it back up to its full
capacity (Figure 2& Figure 5). This process will continue un-
til Enable goes low.
11
www.national.com
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