LTC2952IF datasheet(13/30 Pages) LINER

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LTC2952

2952fa

OPERATION

The LTC2952 is designed to simplify applications requiring

management of multiple power sources. The three main

features of the part are: pushbutton control, ideal diode

PowerPath controllers and system monitoring. The Block

Diagram on the previous page shows the part divided into

its main functional blocks.

The pushbutton detect block is responsible for debouncing

any pushbutton event on the PB 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 pushbutton 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 pushbutton 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 PowerPath controllers and

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

provides system monitoring function via the VM, WDE,

RST and PFI, PFO pins. The voltage monitoring (VM) and

the watchdog (WDE) input pins determine the state of the

RST output with 200ms reset time and 1.6s watchdog

time. The PFI and PFO pins are the input and output of an

accurate comparator that can be used as an early power

fail monitor.

The KILL, 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 PowerPath controllers and the pushbutton control

behavior. Specifically, the KILL 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 configure the part to have different behaviors in the

PowerPath 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

PowerPath controllers are always enabled which results

in an automatic switchover between the two DC sources.

configuration C is similar to A except for the pushbutton

input which now controls both the EN pin and the ideal

diode PowerPath controllers.

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 PowerPath is disabled. In D, M2 needs to be

above threshold before PB has control over the EN pin

and the ideal diode PowerPath controllers. Furthermore

in D, the rising and falling edges on M2 are interpreted as

turn-on and turn-off commands, respectively.

LTC2952IF Datasheet(PDF) 13 Page - Linear Technology

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