in standby mode. If this voltage drops below the4.05V
recharge threshold (V
RECHRG
), another charge cycle
begins and current is once again
supplied to the
battery. To manually restart a charge cycle when in
standby mode, the input voltage must be removed
and reapplied, or the charger must be shut down and
restarted using the PROG pin. Figure 1 shows the
state diagram of a typical charge cycle.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the
input voltage and keeps the charger in shutdown
mode until VCC 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 VCC falls to
within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until VCC rises 100mV above the
battery voltage.
Charge Status Indicator (CHRG)
The charge status output has three different states:
strong pull-down (~10mA), weak pull-down (~20μA)
and high impedance. The strong pull-down state
indicates that the SE9017 is in a charge cycle. Once
the charge cycle has terminated, the pin state is
determined by undervoltage lockout conditions. A
weak pull-down indicates that V
CC
meets the UVLO
conditions and the SE9017 is ready to charge. High
impedance
indicates
that
the
SE9017
is
in
undervoltage lockout mode: either V
CC
is less than
100mV above the BAT pin voltage or insufficient
voltage is applied to the V
CC
pin.
Power On
V
BAT
<2.8V
PROG Reconnected
Or
UVLO Connection Stops
Trickle Charge Mode
1/10
TH
of Full Current
Chrg LED: Strong Pull-Dn
V
BAT
>2.8V
Shutdown Mode
I
CC
Drops to < 20μA
CC/CV Charge Mode
Full Current
Chrg LED: Strong Pull-Dn
V
BAT
>2.8V
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
SE9017
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
SE9017.
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.
Chrg: Hi-Z In UVLO
WeakPull-Dn
Otherwise
V
PROG
<100mV
Standby Mode
No Charge Current
PROG Floated
Or
UVLO Connection
Chrg LED: Weak Pull-Dn
4.05V>V
BAT
>2.8V
Figure1.
State Diagram of a Typical Charge Cycle
Revision 4/16/2009
Preliminary and all contents are subject to change without prior notice
© Seaward Electronics Inc., 2007. • www.seawardinc.com.cn • Page 7
SEAWARD [ Seaward Electronics Inc. ]
