Datasheet
V
TT
LP2998
PV
IN
V
DDQ
V
REF
AV
IN
V
REF
=
1.25V
V
SENSE
GND
+
+
+
V
DDQ
=
2.5V
AV
IN
= 3.3V or 5V
V
TT
=
1.25V
SD
SD
PV
IN
= 3.3V
C
IN
C
OUT
C
REF
V
TT
LP2998
PV
IN
V
DDQ
V
REF
AV
IN
V
REF
=
1.25V
V
SENSE
GND
+
+
+
V
DDQ
=
2.5V
AV
IN
= 2.2V to 5.5V
V
TT
=
1.25V
SD
SD
PV
IN
= 1.8V
C
IN
C
OUT
C
REF
V
TT
LP2998
PV
IN
V
DDQ
V
REF
AV
IN
V
REF
=
1.25V
V
SENSE
GND
+
+
+
V
DDQ
=
2.5V
V
DD
=
2.5V
V
TT
=
1.25V
SD
SD
C
IN
C
OUT
C
REF
LP2998/LP2998-Q1
www.ti.com
SNVS521J –DECEMBER 2007–REVISED DECEMBER 2013
Figure 19. Recommended SSTL-2 Implementation
If power dissipation or efficiency is a major concern then the LP2998 has the ability to operate on split power
rails (see Figure 20). The output stage (PVIN) can be operated on a lower rail such as 1.8V and the analog
circuitry (AVIN) can be connected to a higher rail such as 2.5V, 3.3V or 5V. This allows the internal power
dissipation to be lowered when sourcing current from V
TT
. The disadvantage of this circuit is that the maximum
continuous current is reduced because of the lower rail voltage, although it is adequate for all motherboard
SSTL-2 applications. Increasing the output capacitance can also help if periods of large load transients will be
encountered.
Figure 20. Lower Power Dissipation SSTL-2 Implementation
The third option for SSTL-2 applications in the situation that a 1.8V rail is not available and it is not desirable to
use 2.5V, is to connect the LP2998 power rail to 3.3V (see Figure 21). In this situation AVIN will be limited to
operation on the 3.3V or 5V rail as PVIN can never exceed AVIN. This configuration has the ability to provide the
maximum continuous output current at the downside of higher thermal dissipation. Care should be taken to
prevent the LP2998 from experiencing large current levels which cause the device to exceed the maximum
operating junction temperature. Because of this risk it is not recommended to supply the output stage with a
voltage higher than a nominal 3.3V rail.
Figure 21. SSTL-2 Implementation With Higher Voltage Rails
Copyright © 2007–2013, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LP2998/LP2998-Q1