Datasheet

LTC2952
15
2952fb
LTC2952
DC/DC
SHDN
G1
G2
V1
V2
M1
M2
S1
PB
EN
VS
2952 F03
Q1
ADAPTER
TO SYSTEM
*Q1 AND/OR Q2 PFET CAN
BE REPLACED BY A SCHOTTKY
DIODE WITH G1 AND/OR G2 FLOATING
**EXTERNAL PULL-UP REQUIRED
Q2
BATTERY
*
**
G1/G2
V1/V2
G1STAT
GATE
STAT (ONLY IN
PRIMARY DRIVER)
ANALOG
CONTROLLER
INTERNAL
ENABLE
ON/OFF
VS
V
IN
VS
2952 F02
INPUT
SUPPLY
+
–
OUTPUT
TO LOAD
+
–
+
–
LINEAR GATE
DRIVER AND
VOLTAGE CLAMP
PRIMARY/SECONDARY
IDEAL DIODE DRIVER
A1
APPLICATIONS INFORMATION
Figure 3. PowerPath Configuration A
Figure 2. Detailed Ideal Diode Driver Functional Block Diagram
The LTC2952 is a versatile power management IC with
pushbutton on/off control and system supervisory fea-
tures. The power management function features ideal
diode PowerPath control that provides low loss switcho-
ver between two DC sources. This PowerPath control
behavior is configurable to satisfy various application
requirements.
The LTC2952’s pushbutton input has independently adjust-
able ON and OFF debounce times that control the toggling
of a low leakage open-drain enable output and in some
configurations, the ideal diode PowerPath operation. A
simple interface allows for digital on/off control and proper
system housekeeping prior to power-down.
The LTC2952 also features robust and accurate system
supervisory functions that fit high reliability system ap-
plications. These supervisory functions include power-fail,
voltage monitoring and watchdog reset functions which
can be used to monitor power status and ensure system
integrity.
The Ideal Diode Drivers
In a typical application, each of the ideal diode drivers
is connected to drive an external P-channel MOSFET as
shown in the Block Diagram and Figure 2. When power
is available at V
IN
and the ideal diode driver is enabled,
the ideal diode driver regulates the voltage at the GATE
to maintain a 20mV difference between V
IN
and VS. As
the load current varies, the GATE voltage is controlled to
maintain the 20mV difference.
If the load current exceeds the external PFET’s ability to
deliver the current with a 20mV V
DS
, then the voltage at
the GATE clamps and the PFET behaves as a fixed resistor
causing the forward voltage to increase slightly as the load
current increases. When the VS pin is externally pulled up
above the voltage level at V
IN
, the ideal diode driver shuts
the external PFET off to prevent reverse conduction. Thus
when both the primary and secondary ideal diode drivers are
enabled, the two ideal diode drivers work together to bring
VS to within 20mV of the higher of either V1 or V2.
The G1STAT pin indicates the status of the primary
ideal diode driver. If the external PFET connected to the
primary driver is providing power to VS, the G1STAT
pin is in a high impedance state and when the PFET con-
nected to the primary driver is shut-off, the G1STAT pin
pulls low.
PowerPath CONFIGURATIONS
Configuration A:
Pushbutton Controller with Automatic Switchover
Between WALL Adapter and Battery
In this particular configuration both of the M1 and M2
pins are connected to ground. These connections set
up the LTC2952 to operate with both of the ideal diodes
enabled all the time.
In this application, power from the VS node to the system
is controlled through the EN pin connected to a shutdown