Datasheet

LTC2978A
63
2978afa
For more information www.linear.com/LTC2978A
APPLICATIONS INFORMATION
OVERVIEW
The LTC2978A 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 LTC2978A junction temperature read back are
also available. Odd numbered channels can be configured
to read back sense resistor voltages to provide current
measurements for those channels. Linear Technology
Power System Managers can coordinate operation among
multiple devices using common SHARE_CLK, FAULTB and
CONTROL pins. The LTC2978A utilizes a PMBus compliant
interface and command set.
POWERING THE LTC2978A
The LTC2978A can be powered two ways. The first method
requires that a voltage between 4.5V and 15V be applied
to the V
PWR
pin. See Figure 14. An internal linear regula-
tor converts V
PWR
down to 3.3V which drives all of the
internal circuitry of the LTC2978A.
Alternatively, power from an external 3.3V supply may
be applied directly to the V
DD33
pins 16 and 17 using a
voltage between 3.13V and 3.47V. Tie V
PWR
to V
DD33
pins.
See Figure 15. All functionality is available when using
this alternate power method. The higher voltages needed
for the V
OUT_EN[3:0]
pins and bias for the V
SENSE
pins are
charge-pumped from V
DD33
.
SETTING COMMAND REGISTER VALUES
The command register settings described herein are in
-
tended as a reference and for the purpose of understanding
the registers in a software development environment. In
actual practice, the LTC2978A can be completely config
-
ured for standalone operation with the LTC USB to I
2
C/
SMBus/PMBus controller (DC1613) 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 V
IN_SNS
pin (V
IN
). In all cases, V
IN
must
exceed VIN_ON in order to enable the device to respond
to the CONTROL pin or OPERATION command. When V
IN
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.
Figure 14. Powering LTC2978A Directly from an Intermediate Bus
Figure 15. Powering LTC2978A from External 3.3V Supply
V
PWR
V
DD33
V
DD33
V
DD25
V
IN_SNS
LTC2978A
0.1µF
0.1µF
4.5V < V
PWR
< 15V
GND
0.1µF
*SOME DETAILS
OMITTED FOR CLARITY
2978a F14
V
DD33
V
DD33
V
DD25
V
PWR
LTC2978A
0.1µF
0.1µF
GND
*SOME DETAILS
OMITTED FOR CLARITY
2978a F15
EXTERNAL 3.3V