OPERATION
Thermal Limiting
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise above
a preset value of approximately 120℃.This feature protects
the SGM4054 from excessive temperature and allows the
user to push the limits of the power handling capability of a
given circuit board without risk of damaging the SGM4054.
The charge current can be set according to typical (not
worst-case) ambient temperature with the assurance that
the charger will automatically reduce the current in
worst-case conditions. ThinSOT power considerations are
discussed further in the Applications Information section.
restarts when the battery voltage falls below 4.05V (which
corresponds to approximately 80% to 90% battery capacity).
This ensures that the battery is kept at or near a fully
charged condition and eliminates the need for periodic
charge cycle initiations.
CHRG
output enters a strong
pulldown state during recharge cycles.
POWER ON
BAT < 2.9V
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
SHUTDOWN MODE
I
CC
DROPS TO < 25µA
CHRG: Hi-Z IN UNLO
WEAK PULL-DOWN
OTHERWISE
CHARGE MODE
FULL CURRENT
CHRG: STRONG
PULL-DOWN
PROG < 100mV
STANDBY MODE
NO CHARGE CURRENT
PROG FLOATED
OR
UVLO CONDITION
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
BAT > 2.9V
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
+
rises above the undervoltage lockout threshold. The UVLO
circuit has a built-in hysteresis of 200mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if V
+
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until V
+
rises 100mV above the battery
voltage.
Manual Shutdown
.
At any point in the charge cycle, the SGM4054 can be put
into shutdown mode by removing R
PROG
thus floating the
PROG pin. This reduces the battery drain current to less
than 2µA and the supply current to less than 50µA. A new
charge cycle can be initiated by reconnecting the program
resistor.
In manual shutdown, the
CHRG
pin is in a weak
pull-down state as long as V
+
is high enough to exceed the
UVLO conditions. The
CHRG
pin is in a high impedance
state if the SGM4054 is in undervoltage lockout mode:
either V
+
is within 100mV of the BAT pin voltage or
insufficient voltage is applied to the V
+
pin.
Figure 1. State Diagram of a Typical Charge Cycle
Automatic Recharge
Once the charge cycle is terminated, the SGM4054
continuously monitors the voltage on the BAT pin using a
comparator with a 2ms filter time (t
RECHARGE
). A charge cycle
8
SGM4054
TOREX [ TOREX SEMICONDUCTOR ]
