LTC2978CUP View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2978CUP' PDF : 64 Pages View PDF
LTC2978
Applications Information
Overview
The LTC2978 is a power management IC that is capable
of sequencing, margining, trimming, supervising output
voltage for OV/UV conditions, providing fault management,
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 the
SHARE_CLK, FAULTB and CONTROL pins. The LTC2978
utilizes a PMBus compliant interface and command set.
Powering the LTC2978
The LTC2978 can be powered two ways. The first method
requires that a voltage between 4.5V and 15V be applied
to the VPWR pin. See Figure 14. An internal linear regula-
4.5V < VPWR < 15V
0.1µF 0.1µF
0.1µF
VPWR
VIN_SNS
VDD33
VDD33
VDD25
LTC2978
GND
*SOME DETAILS
OMITTED FOR CLARITY
2978 F14
Figure 14. Powering LTC2978 Directly from an Intermediate Bus
EXTERNAL 3.3V
0.1µF
0.1µF
VPWR
VDD33
VDD33
VDD25
LTC2978
GND
*SOME DETAILS
OMITTED FOR CLARITY
2978 F15
Figure 15. Powering LTC2978 from External 3.3V Supply
tor converts VPWR down to 3.3V which drives all of the
internal circuitry of the LTC2978.
Alternatively, power from an external 3.3V supply may
be applied directly to the VDD33 pins 16 and 17 using a
voltage between 3.13V and 3.47V. Tie VPWR to VDD33 pins.
See Figure 15. All functionality is available when using
this alternate power method. The higher voltages needed
for the VOUT_EN[0:3] pins and bias for the VSENSE pins are
charge pumped from VDD33.
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
the LTC USB to I2C/SMBus/PMBus controller and software
GUI using intuitive menu driven objects.
Sequence, Servo, Margin and Restart
Operations
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
measured at the VIN_SNS pin (VIN). In all cases, VIN must
exceed VIN_ON in order to enable a start. When VIN drops
below VIN_OFF an immediate OFF of all channels will result.
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. A DC/DC converter may be configured to turn on anytime
VIN exceeds VIN_ON.
2. A DC/DC converter may be configured to turn on only
when it receives an OPERATION command.
3. A DC/DC converter may be configured to turn on only
via the CONTROL pin.
4. A DC/DC converter may be configured to turn on only
when it receives an OPERATION command and the
CONTROL pin is asserted.
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For more information www.linear.com/LTC2978
2978fd
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