LX1671CLQ Microsemi Analog Mixed Signal Group, LX1671CLQ Datasheet - Page 17

• Manufacturer Part Number: LX1671CLQ
• Description: IC CTRLR PS QUAD OUTPUT 38MLPQ
• Manufacturer: Microsemi Analog Mixed Signal Group
• Series: LoadSHARE™r

Specifications of LX1671CLQ

• Pwm Type: Voltage Mode
• Number Of Outputs: 4
• Frequency - Max: 345kHz
• Duty Cycle: 85%
• Voltage - Supply: 4.5 V ~ 5.5 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 38-MLPQ
• Frequency-max: 345kHz
• For Use With: LX1671 EVA KIT - KIT EVAL FOR SWITCHING REGULATOR
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Copyright © 2000
Rev. 1.2b, 2006-02-13
Where RSS and C
The current required to charge the output capacitor during the soft
Taking the derivative with respect to time results in
and at t=0
the pulsating current generated by the buck converter to reduce
interference to other circuits connected to the same 5V rail. In
addition, the input capacitor provides local de-coupling for the
buck converter. The capacitor should be rated to handle the RMS
current requirements. The RMS current is:
maximum value occurs when d = 50% then I
input and output in the range of 2 to 3V, the required RMS
current is very close to 0.5I
output voltage rises and how large the inductor current is required
to charge the output capacitor. The output voltage will follow the
voltage at the SS pin if the required inductor current does not
exceed the maximum allowable current for the inductor. The SS
pin voltage can be expressed as:
start interval is.
The required inductor current for the output capacitor to follow
the soft start voltage equals the required capacitor current plus the
load current.
provide the desired power on sequencing and insure that the
overall inductor current does not exceed its maximum allowable
rating.
I
S
NPUT
OFT
The input capacitor and the input inductor, if used, are to filter
Where I
The value of the soft-start capacitor determines how fast the
-S
C
TART
TM
APACITOR
L
is the inductor current and d is the duty cycle. The
C
APACITOR
The soft-start capacitor should be selected to
SS
V
Iout
SS
are the soft-start resistor and capacitor.
I
=
Im
=
RMS
Iout =
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
V
VrefCout
ax
L
RssCss
ref
=
.
=
I
Cout
L
(
1
VrefCout
RssCss
−
d(1
e
dVss
e
−
−
dt
−
t/R
t/R
d)
SS
A P P L I C A T I O N N O T E
SS
C
C
SS
SS
RMS
)
Integrated Products, Power Management
=0.5I
L
. For 5V
®
Microsemi
not allow startup since I
saturation of the output inductor unless very large output capacitors
are used.
O
detected by the current sense comparator is greater than the current
sense comparator threshold, V
R
wide the 350nS delay for current limit enable may result in current
pulses exceeding the desired current limit set point. If the upper
MOSFET on time is less than 350nS and a short circuit condition
occurs the duty cycle will increase, since Vout will be low. The
current limit circuit will be enabled when the upper gate drive
exceeds 350nS although the actual peak current limit value will be
higher than calculated with the above equation.
even though the magnitude of the current pulses will be higher than
the calculated value.
leave them floating.
If OCP is not desired connect both VSX and VCX to VCC. Do not
DS(ON)
VER
Note: Maximum R
At low duty cycles where the upper gate drive is less than 350nS
Short circuit protection still exists due to the narrow pulse width
Values of Css equal to .1uf or greater are unlikely to result in
Current limiting occurs at current level I
So,
Example:
For 10A current limit, using FDS6670A MOSFET (10mΩ
Multiple Output LoadSHARE™ PWM
( C O N T I N U E D )
-C
R
):
URRENT
SET
=
R
P
V
SET
TRIP
RODUCTION
P
I
CL
ROTECTION
=
−
×
SET
0.
I
R
I
CL
CL
SET
3
DS(ON)
50
is 6KΩ. Any resistor 6KΩ or greater will
×
−
will equal zero (50uA x 6KΩ=300mV).
R
10
×
DS(ON)
10
+
×
TRIP
I
0.0
−
D
SET
6
(300mV).
ATA
10
×
=
R
3
=
00
SET
S
. 4
mV
HEET
=
02
V
kΩ
−
50
CL
TRIP
I
µA
CL
when the voltage
1
×
%
R
DS(ON)
LX1671
Page 17