LTC2952
22
2952fb
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 M1 M2 EN ID1 ID2
0 Both Diodes Enabled 0 0 0 1 1
1 Both Diodes Enabled 0 0 1 1 1
2 Primary Diode Off, Secondary
Diode On
01001
3 Primary Diode Off, Secondary
Diode On
01101
4 PowerPath Off, PB Overwrite 1 0 0 0 0
5 Transitional PowerPath Off,
PB Overwrite
10111
6 Pushbutton PowerPath Off 1 1 0 0 0
7 Pushbutton PowerPath On 1 1 1 1 1
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).
