LTC2978
APPLICATIONS INFORMATION
OVERVIEW
tor converts V
down to 3.3V which drives all of the
PWR
internal circuitry of the LTC2978.
The LTC2978 is a power management IC that is capable
of sequencing, margining, trimming, supervising output
voltage for OV/UV conditions, providing fault manage-
ment, and voltage read back for eight DC/DC converters.
Input voltage and LTC2978 junction temperature read
back are also available. Odd numbered channels can be
configured to read back sense resistor voltages. Multiple
LTC2978s can be synchronized to operate in unison using
theSHARE_CLK,FAULTBandCONTROLpins.TheLTC2978
utilizes a PMBus compliant interface and command set.
Alternatively, power from an external 3.3V supply may be
applied directly to the V
age between 3.13V and 3.47V. Tie V
pins 16 and 17 using a volt-
DD33
to V
pins.
PWR
DD33
See Figure 1ꢀ. All functionality is available when using
this alternate power method. The higher voltages needed
for the V
pins and bias for the V
pins are
OUT_EN[±:3]
SENSE
charge pumped from V
.
DD33
SETTING COMMAND REGISTER VALUES
The command register settings described herein are for
the purpose of understanding and software development
in a host processor. In actual practice, the LTC2978 can
be completely configured for standalone operation with
POWERING THE LTC2978
The LTC2978 can be powered two ways. The first method
requires that a voltage between 4.ꢀV and 1ꢀV be applied
2
to the V
pin. See Figure 14. An internal linear regula-
theLTCUSBtoI C/SMBus/PMBuscontrollerandsoftware
PWR
GUI using intuitive menu driven objects.
4.5V < V
< 15V
PWR
V
V
IN_SNS
SEQUENCE, SERVO, MARGIN AND RESTART
OPERATIONS
PWR
0.1µF
0.1µF
0.1µF
V
V
V
DD33
DD33
DD25
LTC2978
GND
Command Units On or Off
Three control parameters determine how a particular
channel is turned on and off. The CONTROL pins, the
OPERATION command and the value of the input voltage
*SOME DETAILS
OMITTED FOR CLARITY
2978 F14
measured at the V
pin (V ). In all cases, V must
IN_SNS
IN IN
Figure 14. Powering LT2978 Directly from an Intermediate Bus
exceed VIN_ON in order to enable a start. When V drops
IN
belowVIN_OFFanimmediateOFFofallchannelswillresult.
Refer to the OPERATION section in the data sheet for a
detailed description of the ON_OFF_CONFIG command.
Some examples of typical ON/OFF configurations are:
1. ADC/DCconvertermaybeconfiguredtoturnonanytime
EXTERNAL 3.3V
0.1µF
V
PWR
V
V
V
DD33
DD33
DD25
LTC2978
GND
V exceeds VIN_ON.
IN
2. A DC/DC converter may be configured to turn on only
when it receives an OPERATION command.
0.1µF
*SOME DETAILS
OMITTED FOR CLARITY
2978 F15
3. A DC/DC converter may be configured to turn on only
via the CONTROL pin.
Figure 15. Powering LTC2978 from External 3.3V Supply
4. A DC/DC converter may be configured to turn on only
when it receives an OPERATION command and the
CONTROL pin is asserted.
2978fc
62
Linear Systems [ Linear Systems ]
