LP3925 Datasheet, PDF (15/51 Pages) Texas Instruments – High Performance Power Management Unit for Handset Applications

Pin/Code
SINK1
SINK2
SINK3
1000
1001
31mA
63 mA
13 mA 25 mA
13 mA 25 mA
1010
94 mA
38 mA
38 mA
1011
1100
1101
Current sink1 max current output
125 mA
156 mA
188 mA
Current sink2 max current output
50 mA
63 mA
75 mA
Current sink3 max current output
50 mA
63 mA
75 mA
1110
219 mA
88 mA
88 mA
1111
250 mA
100 mA
100 mA
Single-Input Linear Charger with
PMOS Routing Switch
LP3925 has a built-in Li-Ion/Li-Poly battery management sys-
tem. Its main features are:
• 1 input with many current limit options to accommodate
different USB and adapter types
• Separate supply branches for battery and system
• Integrated power routing switch
• Charging cycle with precharge, constant current and
constant voltage modes
• Selectable battery regulation voltage to accommodate
different batteries
• Selectable system regulation voltage
• Wide array of battery charging current options
• Flexible charging cycle control
• Temperature monitoring to avoid overheating
• Selectable safety timer
GENERAL CHARGER CONTROL
The charger control is divided into two separate parts: battery
charging and system supply.
Battery charging part of the charger measures battery voltage
and current. Based on this data, it makes the decisions about
starting or ending battery charging and choosing the right
current.
System supply part monitors the power consumption by the
external system, ensures that the system supply is stable and
that the charger input is not overloaded. These systems work
independently from each other.
If the power routing switch is OFF (non-conducting), then they
can be viewed as two separate systems. The only depen-
dence between the two is, that battery charging current can
be reduced, if the system requires more current from the in-
put. If the power routing switch is turned ON, then the two
algorithms still work independently, but the system supply
part is in control of the whole charger. The battery charging
part is in the situation, that it still does make battery charging
cycle decisions, but these do not affect the actual charging.
If the switch is turned OFF again, then the two systems keep
on working separately.
CHARGER INPUT DETECTION AND LIMITS
Input detection is implemented with 2 comparators. One com-
pares the input voltage to the lower limit of the working range,
the other to the higher limit of the working range. If the input
voltage is between these two levels, then the charger is al-
lowed to work.
The lower limit of input's working range is V_BATT+200 mV, with
an option to add a 4.2V minimum requirement. The higher
limit of input's working range can be one of the following val-
ues: 6.15V, 6.64V, 7.18V, 7.71V, 10.28V, 15.38V, 18.45V or
disabled. To get the exact information about your product,
please refer to the Datasheet Addendum document.
The charger is capable of limiting input current, allowing to
accommodate different voltage sources (wall adapters, USB,
etc). IDCIN bits set the maximum input current. The sum of
system supply and battery charging currents will not go over
this limit during normal operation. For correct operation, ID-
CIN should be set to 235mA or more above IBATT (though
this margin can be reduced for IDCIN below 500 mA; e.g.
down to 85 mA at IDCIN = 135 mA). High current mode ig-
nores the input current limit.
Some of the GPIO pins can be configured as a dedicated
charger input status signal output. This signal is low, if charger
input is in working range. The 'Inverted VDCIN' configuration
details are in the GPIO chapter of the datasheet.
SYSTEM SUPPLY FUNCTION
system supply regulator starts to regulate voltage on VDD pin.
The voltage is selectable with VDD control bits. System volt-
age regulator will work as long as charger input is in working
range. The only exception is the case, where PMU is in stand-
by mode and system supply is configured off in standby.
Because system and battery are supplied from separate
branches, the VDD and BATT voltage levels can be different.
This means, that the selected voltage can be supplied to VDD
and the PMU can fully operate, while the battery is deeply
discharged and the charger is in pre-charge mode. In that
case the system should not use modes, which will require
more current, than the input can provide.
System supply is with higher priority than battery charging.
This means that if the sum of system and battery currents
starts to go over the input limit, then battery charging current
will be reduced to stay within the input loading limit.
If the system supply reaches the selected input current limit,
then the power routing switch will be turned ON. This will con-
nect the battery to the system, which will provide the extra
power needed. Also, the system supply current limit will
change from input current limit (IDCIN bits) to battery current
limit (I_BATT bits). This ensures, that if the system load drops,
then the battery will not be charged with too large current.
In some systems it may be practical to disable the input cur-
rent limit, so the system can draw more than 1.2A without
turning the switch ON. The SYSTEM SUPPLY CURLIM OFF
bit can be used for this purpose. Warning: continuous high
current draw from the input may cause the PMU to shut down
because of high temperature. There is a configuration option
for the system supply during PMU's standby mode. The se-
lection for a specific product is shown in Datasheet Adden-
dum document.
This option has following behavior:
a) supply on during PMU standby: VDD is supplied from
BATT via switch (if charger is not working) or from system
supply branch (if charger is working).
b) supply off during PMU standby: VDD is isolated from
BATT pin during PMU standby and system supply branch is
disabled.
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