LTC2952 Linear Technology, LTC2952 Datasheet - Page 16

• Manufacturer Part Number: LTC2952
• Description: Pushbutton PowerPath Controller
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2952
pin of a DC/DC converter. The PB input achieves PowerPath
control by toggling this EN pin.
Note that in this application both of the ideal diodes are
enabled all the time, therefore either Q1 or Q2 can be
replaced by Schottky diodes as long as the voltage drop
across the Schottky diodes and their reverse leakage cur-
rents are acceptable.
Configuration B:
Pushbutton Controller with Preferential WALL Adapter
Operation and Automatic Switchover to Battery
In this configuration (Figure 4) the M1 pin is connected
to ground and the M2 pin is used as a monitor on the
wall adapter input to alter the behavior of the ideal diode
drivers. When the wall adapter voltage is below the trip
threshold, both of the ideal diodes are enabled.
When the wall adapter voltage is above the trip threshold,
the primary ideal diode driver is disabled (shutting off Q1
and Q3) and the secondary ideal diode driver is enabled
(turning on Q2). This means the load current will be sup-
plied from the wall adapter (V2) regardless of the voltage
level at the battery (V1).
If the wall adapter voltage trip threshold is set lower than
the battery input voltage level and the wall adapter input
can go high impedance, the capacitance on V2 needs to
be minimized. This is to ensure proper operation when the
wall adapter goes high impedance and Q1, Q3 is instantly
turned on.
16
WALL ADAPTER
BATTERY
R9
R10
Figure 4. PowerPath Configuration B
Q2
S1
Q1
G2
V1
V2
M1
M2
PB
G1
LTC2952
Q3
VS
2952 F04
EN
DC/DC
SHDN
WALL CAN BE LESS
THAN BATTERY
TO SYSTEM
Noting the possible current path through the PFET body
diode, a back-to-back PFET configuration must be used
for Q1, Q3 to make sure that no current will flow from the
battery (V1) to the VS pin even if the wall adapter (V2)
voltage is less than the battery (V1) voltage.
Configuration C:
Pushbutton Control of Ideal Diode Drivers
In this configuration the M2 pin is tied to the M1 pin.
Since the M1 pin has a 3μA internal pull-up current, this
current causes both M1 and M2 to pull high. This allows
the PB pin to have complete control of both the ideal diode
drivers and the EN pin.
The first valid pushbutton input turns on both of the ideal
diode drivers causing the VS pin to be driven to the higher
of either the wall adapter or the battery input – providing
power to the system directly. Conversely, a valid pushbut-
ton off input turns off the ideal diodes after the shutdown
sequence involving an interrupt to the system.
Configuration D:
Battery Backup with Pushbutton PowerPath Controller
In this configuration shown in Figure 6, the M1 pin is left
floating allowing its own 3μA internal pull-up to pull itself
above threshold. With M1 high, the device operates such
that rising and falling edges on the M2 pin are interpreted
as digital on and off commands respectively.
In Figure 6, the M2 pin monitors the wall adapter voltage.
When power is first applied to the wall adapter so that the
voltage at the M2 pin rises above its rising trip threshold
WALL ADAPTER
BATTERY
Figure 5. PowerPath Configuration C
Q2
S1
Q1
Q4
G2
V1
V2
M1
M2
PB
G1
LTC2952
Q3
VS
2952 F05
EN
TO SYSTEM
2952fa