LTC2952CF datasheet(22/30 Pages) LINER

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LTC2952

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APPLICATIONS INFORMATION

Setting Up Different Configurations

The various configurations discussed previously are sum-

marized in Table 2, including the ideal diode PowerPath

state (ID1-primary, ID2-secondary). Note that an input

above 0.515V (typical rising threshold) on the M1 and

M2 pins is indicated with a 1 and an input below 0.500V

(typical falling threshold) is represented by a 0. Also,

an enabled ideal diode driver is indicated with a 1 and a

disabled driver is indicated with a 0.

Table 2. Mode Table

MODE DESCRIPTION

ID1

ID2

Both Diodes Enabled

Primary Diode Off, Secondary

Diode On

01001

Primary Diode Off, Secondary

Diode On

01101

PowerPath Off, PB Overwrite

Transitional PowerPath Off,

PB Overwrite

10111

Pushbutton PowerPath Off

Pushbutton PowerPath On

In addition to the mode table, the mode transition diagram

in Figure 14 shows all possible interactions between the

events on the pins (PB, M1 and M2) and the different

modes of the LTC2952 PowerPath behavior. Using Table 2

and Figure 14, it is possible to configure the LTC2952 in

many different ways beyond the four discussed in the

Operation and Applications Information sections.

In modes 0 and 1, both of the ideal diode drivers are enabled

all the time. A valid pushbutton toggles the mode between

0 and 1 (changing the state of the EN pin) without ever

turning off of the ideal diodes. These modes are used in

configuration A and B (Figures 3 and 4).

In modes 2 and 3, only V2 provides power to the load

connected at VS because the primary ideal diode driver is

disabled and only the secondary ideal diode driver is en-

abled. These modes are used in configuration B (Figure 4).

In modes 4 and 5 both of the ideal diodes are disabled

and the input to the PB pin is ignored. Note that mode 5

is a transitional mode. If there is no change at the M1 and

M2 pin while in mode 5, the mode eventually transitions

into mode 4 after a proper shutdown sequence.

A rising edge at M1 in mode 1 or a falling edge at M2 in

mode 7 is recognized as a digital off command, which

causes a transition to mode 5. When a digital off com-

mand is received, the EN pin is driven low and the ideal

diodes are disabled after a proper shutdown sequence

involving the interrupt alert to the μP (INT pin driven

low)—refer to the earlier sections for details on the

shutdown sequence.

Note that since the PB input is ignored in both mode 4 and

5, the only way to turn on the PowerPath from these two

modes is a transition from 0 to 1 at the M2 pin. A transition

from 0 to 1 at the M2 pin in modes 4 or 5 is interpreted as

a digital on command. This digital on command causes

the mode to transition from mode 4 or 5 to mode 7. In

mode 7, both of the ideal diodes are enabled and the EN

pin goes high impedance. Modes 4, 5 and 7 are used in

configuration D (Figure 6).

Notice that in mode 7, both the M2 pin and the PB pin

have direct control over the EN pin. A transition from 1

to 0 at the M2 pin in mode 7 is recognized as a digital off

command. This digital off command causes a transition to

mode 4 after a proper shutdown sequence. On the other

hand, a valid pushbutton off mode 7 transitions the part to

mode 6 after a proper shutdown sequence. In both mode 4

and mode 6 the EN pin is driven low. Modes 6 and 7 are

used in configuration C (Figure 5).

In mode 4 the ideal diode driver circuitry is disabled, the

EN pin is driven low, and the PB input is ignored. On the

other hand, in mode 6, although both of the primary and

secondary ideal diodes are disabled and the EN pin is set

low, the PB input is not ignored. A valid pushbutton tran-

sitions the part from mode 6 to mode 7, turning on both

the ideal diodes and setting the EN pin high impedance

(turning on the DC/DC converter).

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