LTC2952CF datasheet(16/30 Pages) LINER

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LTC2952

2952fa

APPLICATIONS INFORMATION

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.

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.

Figure 4. PowerPath Configuration B

LTC2952

DC/DC

SHDN

R10

2952 F04

WALL ADAPTER

TO SYSTEM

WALL CAN BE LESS

THAN BATTERY

BATTERY

Figure 5. PowerPath Configuration C

LTC2952

2952 F05

WALL ADAPTER

TO SYSTEM

BATTERY

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

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