LTC2952CFPBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2952CFPBF' PDF : 30 Pages View PDF
LTC2952
APPLICATIONS INFORMATION
WALL ADAPTER
Q2
BATTERY
R9
C2
R10
S1
Q1
G2 G1
VS
V1
V2
M1 LTC2952 EN
M2
PB
DC/DC
SHDN
TO SYSTEM
2952 F06
Figure 6. PowerPath Configuration D
(0.515V), both of the ideal diode drivers and the DC/DC
converter are enabled. Thus, power is delivered to the
system.
As soon as the wall adapter voltage falls below its trip
threshold, a shutdown sequence is immediately started. At
the end of the shutdown sequence, the ideal diode drivers
and the DC/DC converter are disabled. Thus, power is cut
off from the load and the system is in shutdown.
Note that once power is delivered to the system, the PB pin
can be used to turn off the power. If PB is used to turn off
the power in this configuration, there are two methods to
turn the power back on: a valid pushbutton on event at the
PB pin or a recycling of the wall adapter voltage (bringing
the voltage level at the M2 pin down below and then back
up above its threshold – a digital on command).
Also note that in this application, the voltage threshold of
the wall adapter input (being monitored at the M2 pin) is
usually set higher than the battery input voltage. Therefore,
the only time when power is drawn from the battery (V1
pin) to the load is during the shutdown sequence when
the voltage at the wall adapter input (V2 pin) has collapsed
below the battery input voltage level.
Reverse Battery Protection
To protect the LTC2952 from a reverse battery connection,
place a 1k resistor in series with the respective supply pin
intended for battery connection (V1 and/or V2) and remove
any capacitance on the protected pin. Figure 7 shows a
configuration with a reverse battery protection on the V1
pin. This resistor will limit the amount of current that flows
out of the V1 pin when a battery is connected in reverse
and protect the part.
Note however, this reverse battery protection resistor
should not be too large in value since the V1 and V2 pins
are also used as the anode sense pins of the ideal diode
drivers. When the ideal diode driver is on, the VS pin
supplies most of the quiescent current of the part (60μA
typ) and the supply pin supplies the remaining quiescent
current (20μA typ). Therefore, the recommended 1k reverse
battery protection resistor amounts to an additional 20mV
(1k • 20μA) drop across the P-channel MOSFET.
In Figure 7, when the battery voltage is larger than the wall
adapter voltage, the battery supplies the load current to
the DC/DC converter. The ideal diode driver regulates G1
to maintain a fixed voltage drop from V1 to VS of 20mV
(typ). Since there is a 20mV drop across the reverse battery
protection resistor (R1) then the regulated voltage drop
from the battery to the VS pin is 40mV (typ).
WALL ADAPTER
BATTERY
Q2
Q1
R12
1k
G2 G1
* V1
DC/DC
SHDN
VS
EN
V2
M1 LTC2952
M2
PB
S1
*MINIMIZE CAPACITANCE ON V1
2952 F07
Figure 7. Reverse Battery Protection on V1
Pushbutton Input and Circuitry
The PB pin is a high impedance input to an accurate com-
parator with a 10μA pull-up to an LDO regulated internal
supply of 4V. The PB input comparator has a 0.775V falling
trip threshold with 25mV hysteresis. Protection circuitry
allows the PB pin to operate over wide range from –6V
to 28V with an ESD HBM rating of ±8kV.
The pushbutton circuitry debounces the input into the PB
pin that sets an internal ON/OFF signal. This signal initiates
a turn ON/OFF power sequence.
2952fa
17
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