LTC2952CF datasheet(13/28 Pages) LINER

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LTC2952

2952f

OPERATION

The LTC2952 is designed to simplify applications requiring

management of multiple power sources. The three main

features of the part are: push-button control, ideal diode

power paths and system monitoring. The block diagram

on the previous page shows the part divided into its main

functional blocks.

The push-button detect block is responsible for debounc-

ing any push-button event on the

⎯P⎯B pin. Note that the ON

and OFF debounce times can be conﬁgured independently

by using two separate capacitors on the ONT and OFFT

pins respectively. A valid push-button on event will set

the EN pin high impedance and a valid off event will drive

the EN pin low.

In a typical application the EN pin is tied to the shutdown

pin of a DC/DC converter. Therefore by toggling the EN pin,

the push-button pin has a direct control over the enabling/

disabling of an external DC/DC converter. This control of

system turn-on/off is done in a graceful manner which

ensures proper system power up and power down.

The ideal diode drivers regulate two external P-channel

MOSFETs to achieve low loss switchover between two DC

sources. Each driver regulates the gate of the PFET such

that the voltage drop across its source and drain is 20mV.

When the load current is larger than the PFET ability to

deliver such current with a 20mV drop across its source

and drain, the voltage at the gate clamps at VG(ON) and

the PFET behaves like a ﬁxed value resistor.

Besides providing ideal-diode power paths and control

of system power turn-on/off, the LTC2952 also provides

system monitoring function via the VM, WDE,

⎯R⎯S⎯TandPFI,

⎯P⎯F⎯O pins. The voltage monitoring (VM) and the watchdog

(WDE) input pins determine the state of the

⎯R⎯S⎯Toutputwith

200ms reset time and 1.6s watchdog time. The PFI and

⎯P⎯F⎯O

pins are the input and output of an accurate comparator

that can be used as an early power fail monitor.

The

⎯K⎯I⎯L⎯L, M1 and M2 pins are the inputs to accurate

comparators with 0.5V threshold. The outputs of these

comparators interact with the logic block to alter the ideal-

diode power paths and the push-button control behavior.

Speciﬁcally, the

⎯K⎯I⎯L⎯L input provides the system with a

capability to turn off system power at any point during

operation. The M1 and M2 pins are mode pins that con-

ﬁgure the part to have different behaviors in the power

path switchover of the two DC sources.

Figure 1 shows the four different typical conﬁgurations

of the LTC2952. In Conﬁguration A, both of the ideal-

diode power paths are always enabled which results in

an automatic switchover between the two DC sources.

Conﬁguration C is similar to A except for the push-button

input which now controls both the EN pin and the ideal

diode power paths.

In Conﬁgurations B and D, M2 is used as a voltage monitor.

In B, when the M2 input is above its threshold the primary

ideal diode power path is disabled. In D, M2 needs to be

above threshold before

⎯P⎯B has control over the EN pin

and the ideal diode power paths. Furthermore in D, the

rising and falling edges on M2 are interpreted as turn-on

and turn-off commands respectively.

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