ADP3155 Analog Devices, ADP3155 Datasheet - Page 7

• Manufacturer Part Number: ADP3155
• Description: 5-Bit Programmable Triple Power Supply Controller for Pentium III Processors
• Manufacturer: Analog Devices

Power Good
The ADP3155 has an internal monitor that senses the output
voltage and drives the PWRGD pin of the device. This pin is an
open drain output whose high level (when connected to a pull-
up resistor) indicates that the output voltage has been within a
The PWRGD pin will go low if the output is outside the regula-
tion band for more than 500 s.
Output Crowbar
An added feature of using an N-channel MOSFET as the syn-
chronous switch is the ability to crowbar the output with the
same MOSFET. If the output voltage is 15% greater than the
targeted value, the ADP3155 will turn on the lower MOSFET,
which will current-limit the source power supply or blow its
fuse, pull down the output voltage, and thus save the micropro-
cessor from destruction. The crowbar function releases at ap-
proximately 50% of the nominal output voltage. For example, if
the output is programmed to 2.0 V, but is pulled up to 2.3 V or
above, the crowbar will turn on the lower MOSFET. If in this
case the output is pulled down to less than 1.0 V, the crowbar
will release, allowing the output voltage to recover to 2.0 V if
the fault condition has been removed.
Shutdown
The ADP3155 has a shutdown (SD) pin that is pulled down by
an internal resistor. In this condition the device functions nor-
mally. This pin should be pulled high to disable the output drives.
APPLICATION INFORMATION
A number of power conversion requirements must be consid-
ered when designing an ACPI compliant system. In normal
operating mode, 12 V, 5 V and 3.3 V are available from the
main supply. These voltages need to be converted into the
appropriate supply voltages for the Northbridge core, the
Southbridge core and RAMBUS memory, as well as supplies for
GTL and I/O drivers, CMOS memory and clock and graphics
(AGP) circuits.
REV. A
5% regulation band of the targeted value for more than 500 s.
(OR NLX)
SUPPLY
POWER
ATX_SHUTDOWN
ATX
ATX_PGOOD
5V_ALWAYS
VDDQ FOR AGP
TYPEDET# FOR
GND
3.3V
AGP SELECT
12V
1.5V OR 3.3V
5V
MEM, ETC
SB CORE,
1.8V FOR
FOR GTL
1.5V VTT
12V
5V
3.3V
5V_PM
ATX_POWERGOOD
ATX_SHUTDOWN
OUT
OUT
VDDQ
SELECT
OUTPUT
SUPPLY
DUAL
POWER ROUTING
Figure 14. ACPI-Compliant Pentium III System Block Diagram
SWITCHER
POWER MANAGEMENT
LINEAR
ATX_POWER GOOD
STATE COMMAND
3.3V_IN
1.5V_IN
CTRLS
CTRLS
IN
IN
5V_PM
CTRLS
MAIN_
12V
V
CC
ADP3156
5V
3.3V
ATXPG
PMSC
5V_PM
CTRLS
LIN_
–7–
MANAGEMENT
FUNCTIONS
CTRLS
During the standby operating state, the 12 V, 5 V and 3.3 V
power supply outputs are disabled, and only a low power 5 V
rail (5VSB) is available. The circuits that must remain active in
standby must be able to run from 5VSB. To accomplish this,
power routing is required to allow switching between normal
and standby supplies. Lack of a 12 V rail in standby makes control
of linear outputs difficult, and with up to 8 A demand from the
1.5 V and 1.8 V rails, an all-linear solution is inefficient.
Figure 14 shows a typical ACPI-compliant Pentium III/chipset
power management system using the ADP3155 and ADP3156.
The ADP3155 provides VID switched output and two linear
regulators for standby operation. A charge-pump-doubled 5VSB is
ORed into the supply rail to supply the linear regulators during
standby operation. The VID output collapses when the main
5 V rail collapses, but the N-channel MOSFET linear regu-
lators can continue to supply current from the ~9 V supply.
The ADP3156 provides 1.8 V via its main switching regulator,
and allows efficient linear regulation of 1.5 V rail by using the
1.8 V output as its source.
Specifications for a Design Example
The design parameters for a typical 300 MHz Pentium II appli-
cation (Figure 2) are as follows:
Maximum Output Current:
Minimum Output Current:
Static tolerance of the supply voltage for the processor core:
LIN#2_
POWER
Input Voltage: V
Auxiliary Input: V
Output Voltage: V
I
I
OMAX
OMIN
V
V
5V_PM
5V_PM
ADP3155
OST+
OST–
5V
= 0.8 A dc
= 14.2 A dc
= –60 mV
LIN#1_
CTRLS
= 100 mV
V
CC
12V
V
IN
VID_4:0
CC
CC
O
CTRLS
MAIN_
= 5 V
= 2.8 V
= 12 V
IN
CTRLS
CTRLS
CTRLS
IN
IN
SWITCHER
LINEAR#1
LINEAR#2
VID
OUTPUT
SUPPLY
TRIPLE
OUT
OUT
OUT
ADP3155
CPU
V
3.3V_PM
FOR POWER
MANAGEMENT
2.5V_PM
FOR CMOS,
CLOCK, MEMORY
CORE
@ VID