MAX1898EUB42 Просмотр технического описания (PDF) - Maxim Integrated
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MAX1898EUB42 Datasheet PDF : 12 Pages
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Linear Charger for Single-Cell Li+ Battery
4.2
4.0
3.8
3.6
3.4
3.2
0
1.4
BATTERY VOLTAGE
1.2
AMP HOURS
1.0
0.8
BATTERY CURRENT
0.6
0.4
POWER DISSIPATION
0.2
0
30 60 90 120 150 180
TIME (MINUTES)
Figure 2. Li+ Charging Profile
the ISET pin is 1mA per amp of charging current. The
output voltage at ISET is proportional to charging cur-
rent as follows:
VISET
=
ICHG × RSET
1000
Reinitiating a Charging Cycle
The MAX1898 can be configured so that a charging
cycle automatically restarts when the cell voltage drops
200mV below the battery regulation voltage (connect
RSTRT to GND). The restart threshold can also be low-
ered by connecting an external resistor between RSTRT
and GND. If automatic charging restart is not desired,
this feature may be disabled by floating the RSTRT pin.
With restart disabled, charging can only be reinitiated
by pulling EN/OK low, or by removing and reapplying
the input power source.
EN/OK (EN Input, OK Output)
The EN/OK pin serves two functions. It primarily serves as
a logic input (active high) to enable the charger. In addi-
tion to ON/OFF control, EN/OK also indicates when input
power is connected. When input power is applied to IN
(VIN > VBATT and VIN > 4.25V) EN/OK pulls high (to 3V)
with a 100kΩ internal pullup resistance. Consequently,
EN/OK may be output to a logic input, to indicate AC
adapter presence, but at the same time may be driven by
open-drain logic to turn the charger ON and OFF. An
open-drain logic-low input will over-ride the internal pullup
resistor and turn off the charger (see Figure 3). When the
open drain goes high impedance, EN/OK will go high if
The voltage at ISET is nominally 1.4V at the selected
fast-charge current, and falls with charging current as
the cell becomes fully charged. See Figure 2 for typical
Li+ charging profile.
CHG Status Output
CHG is an open-drain output that monitors the cell’s
charging status. CHG has a 5mA current limit so an
LED can be connected directly from IN to CHG for a
visible indication. Alternatively, a pullup resistor (typi-
cally 100kΩ) to a logic supply provides a logic-level
output. Table 1 outlines the status of CHG for various
charger states.
Table 1. CHG Output States
POWER OK
IN
OFF
ON
OPEN-DRAIN
LOGIC
3V
100kΩ
EN/OK
MAX1898
GND
Figure 3. Driving EN/OK with Open-Drain Logic to Retain
ON/OFF Control with Power OK Indication
CONDITION
No battery or no charger input.
The cell voltage is less than 2.5V and charge current is regulated to 10% of the selected fast-
charge current (prequalification state).
Cell voltage is greater than 2.5V (fast-charge state).
Charge cycle complete—charge current is less then 20% of the selected fast charge current or
safety timer expires (3 hours for CCT = 100nF).
Charge cycle fault—the cell voltage is less than 2.5V and the prequalification timer (45min for CCT
= 100nF) has expired.
CHG
High impedance (LED off)
Low impedance (LED on)
Low impedance (LED on)
High impedance (LED off)
Blinking, LED on 50% duty
factor, 1.5Hz
8 _______________________________________________________________________________________
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