Datasheet
www.ti.com
DETAILED DESCRIPTION
Battery Freshness Seal (TPS3619)
Power-Fail Comparator (PFI and PFO)
Backup-Battery Switchover
TPS3619-33 , , TPS3619-50
TPS3620-33 , TPS3620-50
SLVS387H – APRIL 2001 – REVISED DECEMBER 2007
The battery freshness seal of the TPS3619 family disconnects the backup-battery from internal circuitry until it is
needed. This function prevents the backup-battery from being discharged unitl the final product is put to use. The
following steps explain how to enable the freshness seal mode.
1. Connect V
BAT
(V
BAT
> V
BAT
min)
2. Ground PFO
3. Connect PFI to V
DD
(PFI = V
DD
)
4. Connect V
DD
to power supply (V
DD
> V
IT
) and keep connected for 5 ms < t < 35 ms
The battery freshness seal mode is automatically removed by the positive-going edge of RESET when V
DD
is
applied.
An additional comparator is provided to monitor voltages other than the nominal supply voltage. The
power-fail-input (PFI) is compared with an internal voltage reference of 1.15 V. If the input voltage falls below the
power-fail threshold V
IT(PFI)
of typical 1.15 V, the power-fail output ( PFO) goes low. If V
IT(PFI)
goes above V
(PFI)
,
plus about 12-mV hysteresis, the output returns to high. By connecting two external resistors, it is possible to
supervise any voltages above V
(PFI)
. The sum of both resistors should be about 1 M Ω , to minimize power
consumption and also to assure that the current in the PFI pin can be ignored compared with the current through
the resistor network. The tolerance of the external resistors should be not more than 1% to ensure minimal
variation of sensed voltage. If the power-fail comparator is unused, PFI should be connected to ground and PFO
left unconnected.
In case of a brownout or power failure, it may be necessary to preserve the contents of RAM. If a backup battery
is installed at V
BAT
, the device automatically switches the connected RAM to backup power when V
DD
fails. In
order to allow the backup battery (e.g., a 3.6-V lithium cell) to have a higher voltage than V
DD
, these supervisors
do not connect V
BAT
to V
OUT
when V
BAT
is greater than V
DD
. V
BAT
only connects to V
OUT
(through a 15- Ω switch)
when V
DD
falls below V
IT
and V
BAT
is greater than V
DD
. When V
DD
recovers, switchover is deferred either until
V
DD
crosses V
BAT
, or until V
DD
rises above the reset threshold V
IT
. V
OUT
connects to V
DD
through a 1- Ω (max)
PMOS switch when V
DD
crosses the reset threshold.
FUNCTION TABLE
V
DD
> V
BAT
V
DD
> V
IT
V
OUT
1 1 V
DD
1 0 V
DD
0 1 V
DD
0 0 V
BAT
10 Submit Documentation Feedback Copyright © 2001 – 2007, Texas Instruments Incorporated
Product Folder Link(s): TPS3619-33 TPS3619-50 TPS3620-33 TPS3620-50