Linear Technology LTC2977 Demo Board: Octal Power Supply Manager [Requires DC1613] DC2028A DC2028A Data Sheet
Product codes
DC2028A
LTC2977
76
2977fa
For more information
applicaTions inForMaTion
OVERVIEW
The LTC2977 is a power management IC that is capable
The LTC2977 is a power management IC that is capable
of sequencing, margining, trimming, supervising output
voltage for OV/UV conditions, providing fault management,
and voltage readback for eight DC/DC converters. Input
voltage and LTC2977 junction temperature readback 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 LTC2977 utilizes a PMBus compliant
interface and command set.
POWERING THE LTC2977
The LTC2977 can be powered two ways. The first method
The LTC2977 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 15. An internal linear regula-
tor converts V
PWR
down to 3.3V which drives all of the
internal circuitry of the LTC2977.
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 16. 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-
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 LTC2977 can be completely configured
for standalone operation with the LTC USB to I
2
C/SMBus/
PMBus controller (DC1613) and software GUI using intui-
tive menu driven objects.
SEqUENCE, SERVO, MARGIN AND RESTART
OPERATIONS
Command Units On or Off
Three control parameters determine how a particular
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 or
sequence off after TOFF_DELAY of all channels will result
(See Mfr_config_chan_mode). 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
Some examples of typical ON/OFF configurations are:
1. A DC/DC converter may be configured to turn on anytime
V
IN
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.
Figure 15. Powering LT2977 Directly from an Intermediate Bus
Figure 16. Powering LTC2977 from External 3.3V Supply
V
PWR
V
DD33
V
DD33
V
DD25
V
IN_SNS
LTC2977*
0.1µF
0.1µF
4.5V < V
PWR
< 15V
GND
0.1µF
*SOME DETAILS
OMITTED FOR CLARITY
2977 F15
V
DD33
V
DD33
V
DD25
V
PWR
LTC2977*
0.1µF
0.1µF
GND
*SOME DETAILS
OMITTED FOR CLARITY
2977 F16
EXTERNAL 3.3V