
7
SS (Pin 17 SOIC; Pin 14 QFN)
Connect this pin to a small ceramic capacitor (no less than 
5nF; 0.1μF recommended). The internal soft-start (SS) 
current source along with the external capacitor creates a 
voltage ramp used to control the ramp-up of the output 
voltages. Pulling this pin low (to GND) with an open-drain 
device shuts down all the outputs as well as forces the 
FAULT pin low. The C
SS
 capacitor is also used to provide a 
controlled voltage slew rate during active-to-sleep transitions 
on the 3.3V
DUAL
/3.3V
SB
 output.
3V3DL (Pin 4 SOIC; Pin 1 QFN)
Connect this pin to the 3.3V dual/stand-by output (V
OUT3
). 
In sleep states, the voltage at this pin is regulated to 3.3V; in 
active states, ATX 3.3V output is delivered to this node 
through a fully-on NFET transistor. During all operating 
states, this pin is monitored for undervoltage events. This pin 
provides all the output current delivered by V
OUT1
.
3V3DLSB (Pin 3 SOIC; Pin 20 QFN)
Connect this pin to the base of a suitable NPN transistor. In 
sleep state, this transistor is used to regulate the voltage at 
the 3V3DL pin to 3.3V.
DLA (Pin 13 SOIC; Pin 10 QFN)
This pin is an open-collector output. Connect a 1k
 resistor 
from this pin to the ATX 12V output. This resistor is used to 
pull the gates of suitable NFETs to 12V, which in active 
state, switch in the ATX 3.3V and 5V outputs into the 
3.3V
DUAL
/3.3V
SB
 and 5V
DUAL
 outputs, respectively.
5VDL (Pin 15 SOIC; Pin 12 QFN)
Connect this pin to the 5V
DUAL
 output (V
OUT4
). In either 
operating state (when on), the voltage at this pin is provided 
through a fully-on MOSFET transistor. This pin is also 
monitored for undervoltage events.
5VDLSB (Pin 14 SOIC; Pin 11 QFN)
Connect this pin to the gate of a suitable PFET or bipolar 
PNP. This transistor is switched on, connecting the ATX 
5V
SB
 output to the 5V
DUAL
 regulator output during S3, and 
if EN5 is open or high, during S5. If EN5 is low (GND), the 
transistor is switched off in S5.
DR1 (Pin 2 SOIC; Pin 19 QFN)
This output pin drives the gate of an external NFET 
transistor to create V
OUT1
, which draws its output current 
from the 3V3DL pin.
FB1 (Pin 1 SOIC; Pin 18 QFN)
This analog input pin looks at the V
OUT1
 external resistor 
divider, and compares it to the internal reference (0.8V 
nominal), in order to regulate the voltage on V
OUT1
. This pin 
is also monitored for undervoltage events.
1V2VID (Pin 5 SOIC; Pin 2 QFN)
This pin is the output of the internal 1.2V voltage identification 
(VID) regulator (V
OUT2
). This internal regulator operates only 
in active states (S0, S1/S2) and is shut off during any sleep 
state. This regulator draws its output current from the 3V3 pin. 
This pin is monitored for undervoltage events.
VID_PG (Pin 18 SOIC; Pin 15 QFN)
This pin is the open collector output of the 1V2VID power 
good comparator. Connect a 10k
 
pull-up resistor from this 
pin to the 1V2VID output. As long as the 1V2VID output is 
below its PG threshold (typically 90% of final value), this pin 
is pulled low. Once the PG threshold is reached, the VID_CT 
pin starts charging its capacitor (setting the delay); when it 
reaches its trip point, then the VID-PG pin releases, and 
goes high (through the external pull-up resistor).
VID_CT (Pin 19 SOIC; Pin 16 QFN)
Connect a small capacitor from this pin to ground. The 
capacitor is used to delay the VID_PG reporting the 1V2VID 
has reached power good limits.
Description
Operation
The ISL6505 controls 4 output voltages (Refer to Figures 1, 
2, and 3). It is designed for microprocessor computer 
applications with 3.3V, 5V, 5V
SB
, and 12V bias input from an 
ATX power supply. The IC is composed of three linear 
controllers/regulators supplying the computer system’s 
V
OUT1
 (1.2V - 1.5V programmable), 3.3V
SB
 and PCI slots’ 
3.3V
AUX
 power (V
OUT3
), the 1.2V VID circuitry power 
(V
OUT2
), a dual switch controller supplying the 5V
DUAL
voltage (V
OUT4
), as well as all the control and monitoring 
functions necessary for complete ACPI implementation.
Initialization and POR
The ISL6505 automatically initializes upon receipt of input 
power. The Power-On Reset (POR) function continually 
monitors the 5V
SB
 input supply voltage, initiating 
3.3V
DUAL
/3.3V
SB
 and 1.5V
SB
 soft-start operation shortly 
after exceeding POR threshold.
Note that while the 5VSB pin has the main POR, both the 
3V3 and 5V pins (12V is not monitored) must rise above 
their own POR levels (typically 90%) in order to transition 
into the S0/S1 active state. If during normal operation either 
one drops below their falling trip points, the IC will go to the 
S5 sleep mode. When both are back above their rising 
thresholds, the IC will again soft-start into active state.
Output Operational Truth Tables
Table 1 describes the truth combinations pertaining to the 
3.3V
DUAL/SB
 and 5V
DUAL 
dual outputs. The last two lines 
highlight the difference between EN5 connected high or low.
Table 2 describes the truth combinations pertaining to the 
V
OUT1
 (typically between 1.2V and 1.5V) and 1V2VID 
outputs. The last two sets of lines highlight the difference 
between the two LAN pin modes (5V/open is the 10/100 LAN 
mode; GND is the Gigabit Ethernet mode).
ISL6505