Datasheet

LTC2974
80
2974fc
For more information www.linear.com/LTC2974
V
PWR
V
DD33
V
DD33
V
DD25
V
DD25
V
IN_SNS
LTC2974*
0.1µF
0.1µF
4.5V < V
PWR
< 15V
GND
0.1µF
*SOME DETAILS
OMITTED FOR CLARITY
2978 F23
applicaTions inForMaTion
OVERVIEW
The LTC2974 is a power management IC that is capable
of sequencing, margining, trimming, supervising output
voltage for OV/UV conditions, supervising output current
for OC/UC conditions, fault management, and voltage/
current/temperature readback for four DC/DC converter
channels. Input voltage and LTC2974 junction temperature
readback are also available. Linear Technology Power
System Managers can coordinate operation among mul
-
tiple devices using common SHARE_CLK, FAULTB, and
CONTROL pins. The LTC2974 utilizes a PMBus compliant
interface and command set.
POWERING THE LTC2974
The LTC2974 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 23. An internal linear regula-
tor converts V
PWR
down to 3.3V which drives all of the
internal circuitry of the LTC2974.
Alternatively, power from an external 3.3V supply may be
applied directly to the V
DD33
pins 11 and 12 using a voltage
between 3.13V and 3.47V. See Figure 24. Tie V
PWR
to the
Figure 23. Powering LTC2974 Directly from an Intermediate Bus
V
DD33
pins. All functionality is available when using this
alternate power method. The higher voltages needed for
the V
OUT_EN
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 LTC2974 can be completely configured
for stand-alone operation with the LTC USB to I
2
C/SMBus/
PMBus controller (DC1613) and software GUI using intui-
tive menu driven objects.
S
EQUENCE, SERVO, MARGIN AND RESTART
OPERATIONS
Command Units On or Off
Three control parameters determine how a particular chan
-
nel 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, VIN must exceed VIN_ON in
order to enable the device to respond to the CONTROL pins
or OPERATION commands. When V
IN
drops below VIN_OFF
an immediate OFF or sequence off after TOFF_DELAY of all
channels will result (See Mfr_config_track_enn). 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 any
time 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.
On Sequencing
The TON_DELAY command sets the amount of time that
V
DD33
V
DD33
V
DD25
V
DD25
V
PWR
LTC2974*
0.1µF
0.1µF
GND
*SOME DETAILS
OMITTED FOR CLARITY
2978 F24
EXTERNAL 3.3V
Figure 24. Powering LTC2974 from External 3.3V Supply