LX1671
I N T E G R A T E D
P R O D U C T S
Multiple Output LoadSHARE™ PWM
P
RODUCTION
D
ATA
S
HEET
FUNCTIONAL PIN DESCRIPTION
N
AME
FB1
EOX
FB3
D
ESCRIPTION
Bi-Phase Operation:
Phase 1 and 2 Voltage Feedback
Single Phase Operation:
Phase 1 Voltage Feedback , connect to the output through a resistor network to set
desired output voltage of Phase 1
Error Amplifier Output – Sets external compensation for the corresponding phase denoted by “X”.
Phase 3 Voltage Feedback , connect to the output through a resistor network to set desired output voltage of
Phase 3.
Bi-Phase Operation:
Load Sharing Voltage Sense Feedback – Connect filtered phase 2 switching output (pre-
inductor) to FB2 to ensure proper current sharing between phase 1 and phase 2.
Single Phase Operation:
Phase 2 Voltage Feedback, connect to the output through a resistor network to set
desired output voltage of Phase 2.
B-Phase Operation:
Load Sharing Voltage Sense Feedback Reference – Sets reference for current sharing
control loop. Connecting filtered phase 1 switching output (pre-inductor) to REF
2
forces average current in
phase 2 to be equal to phase 1.
Single Phase Operation:
Phase 2 Voltage Reference – connected to SS2 pin as a reference.
IC supply voltage (nominal 5V).
Low Dropout Regulator Voltage Feedback – Sets output voltage of external MOSFET via resistor network.
Over-Current Limit Set – Connecting a resistor between CS pin and the source of the high-side MOSFET sets the
current-limit threshold for the corresponding phase denoted by “X”. Exceeding the current-limit threshold forces
the corresponding phase into hiccup mode protection. A minimum of 1KΩ must be in series with this input.
Enable & Soft-start/Hiccup Capacitor Pin – During start-up, the voltage on this pin controls the output voltage of
its respective regulator. An internal 20kΩ resistor and the external capacitor set the time constant for soft-start
function. The Soft-start function does not initialize until the supply voltage exceeds the UVLO threshold. When
an over-current condition occurs, this capacitor is used for the timing of hiccup mode protection. Pulling the SS
pin below 0.3V disables the corresponding phase denoted by “X”.
Analog ground reference.
Digital ground reference.
Low Dropout Regulator Gate Drive – Connects to gate of external N-Channel MOSFET for linear regulator
function.
Driver Power Ground. Connects to the source of the bottom N-channel MOSFETS of phase 1& 2 where X=1,
and phase 3 where X=3.
High Side MOSFET Gate Driver – “X” denotes corresponding phase.
Low Side MOSFET Gate Driver – “X” denotes corresponding phase.
WWW .
Microsemi
.C
OM
FB2
RF2
VCC
LDFB
CSX
SSX
AGND
DGND
LDGD
PGX
HOX
LOX
VCX
LDDIS
VCCL
VSX
RSVD
P
ACKAGE
D
ATA
P
ACKAGE
D
ATA
Phase High-Side MOSFET Gate Driver Supply – Connect to separate supply or boot strap supply to ensure
proper high-side gate driver supply voltage. “X” denotes corresponding phase. If the phase is not used connect to
VCC
Active High disables LDO output.
Power Supply pin for all Low side drivers.
Voltage reference for Current sense. This pin is also the supply pin for the Current Sense Comparator.
“X” denotes corresponding phase. This pin cannot be left floating, if a phase is not used connect to VCC.
Do not make any connection to this pin
Copyright
©
2000
Rev. 1.0a, 2004-06-14
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
MICROSEMI [ MICROSEMI CORPORATION ]
