IRU3018
5
Rev. 1.6
07/16/02
www.irf.com
This pin has dual function. It acts as an output of the OVP circuitry or it can be used to
program the frequency using an external resistor. When used as a fault detector, if the
switcher output exceeds the OVP trip point, the Fault pin switches to 12V and the soft-
start cap is discharged. If the Fault pin is to be connected to any external circuitry, it
needs to be buffered as shown in the application circuit.
This pin provides the feedback for the internal LDO regulator which its output is VOUT4.
This pin is the input that provides power for the internal LDO regulator. It is also monitored
for the under-voltage and over-voltage conditions.
This pin is the output of the internal LDO regulator.
This pin serves as the ground pin and must be connected directly to the ground plane.
This pin controls the gate of an external transistor for the 1.5V GTL+ linear regulator.
This pin provides the feedback for the linear regulator which its output drive is Gate3.
This pin is a TTL compatible Enable pin. When this pin is left open or pulled high, the
device is enabled and when it is pulled low, it will disable the switcher and the LDO
controller (VOUT3) leaving the internal 200mA regulator operational. When signal is given to
enable the device, both switcher and VOUT3 will go through soft-start, the same as during
start-up.
This pin provides the feedback for the synchronous switching regulator. Typically this pin
can be connected directly to the output of the switching regulator. However, a resistor
divider is recommended to be connected from this pin to VOUT1 and Gnd to adjust the
output voltage for any drop in the output voltage that is caused by the trace resistance.
The value of the resistor connected from VOUT1 to Fb1 must be less than 100V.
This pin is internally connected to the under-voltage and over-voltage comparators sens-
ing the Vcore status. It must be connected directly to the Vcore supply.
This pin is connected to the Drain of the power MOSFET of the Core supply and it provides
the positive sensing for the internal current sensing circuitry. An external resistor pro-
grams the CS threshold depending on the RDS of the power MOSFET. An external capaci-
tor is placed in parallel with the programming resistor to provide high frequency noise
filtering.
This pin serves as the Power ground pin and must be connected directly to the ground
plane close to the source of the synchronous MOSFET. A high frequency capacitor (typi-
cally 1mF) must be connected from V12 pin to this pin for noise free operation.
Output driver for the synchronous power MOSFET for the Core supply.
This pin is connected to the Source of the power MOSFET for the Core supply and it
provides the negative sensing for the internal current sensing circuitry.
Output driver for the high side power MOSFET for the Core supply.
PIN# PIN SYMBOL PIN DESCRIPTION
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Fault / Rt
Fb2
VIN2
VOUT2
Gnd
Gate3
Fb3
En
Fb1
VSEN1
OCSet1
PGnd
LGate1
Phase1
UGate1
