LX1661CD Microsemi Analog Mixed Signal Group, LX1661CD Datasheet - Page 12
LX1661CD
Manufacturer Part Number
LX1661CD
Description
IC PWM MONO SWITCHING REG 16SOIC
Manufacturer
Microsemi Analog Mixed Signal Group
Datasheet
1.LX1660CD.pdf
(15 pages)
Specifications of LX1661CD
Applications
Controller, Intel Pentium®
Voltage - Input
10.8 ~ 13.2 V
Number Of Outputs
1
Voltage - Output
2V
Operating Temperature
0°C ~ 70°C
Mounting Type
Surface Mount
Package / Case
16-SOIC
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LX1661CD
Manufacturer:
LINFINITR
Quantity:
20 000
LX1660/1661
12
CURRENT LIMIT
table:
Loss-Less Current Sensing Using Resistance of Inductor
Any inductor has a parasitic resistance, R
voltage drop when current flows through the inductor. Figure 8
shows a sensor circuit comprising of a surface mount resistor, R
and capacitor, C
current sense resistor.
If the sensor components are selected such that:
flowing through the resistor, i.e.
priate R
voltage at the desired trip current.
Design Example
(Pentium II circuit, with a maximum static current of 14.2A)
The gain of the sensor can be characterized as:
Copper
Weight
2 oz/ft
Recommended sense resistor sizes are given in the following
The current flowing through the inductor is a triangle wave.
The voltage across the capacitor will be equal to the current
Since V
L/R
V
CS
2
TABLE 3 - PCB Sense Resistor Selection Guide
S
L
= I
L/R
= R
CS
and C
Thickness
L
Copper
reflects the inductor current, by selecting the appro-
R
S
68µm
|T(j )|
S
C
R
L
FIGURE 8 — Current Sense Circuit
* C
S
L
Comparator
(continued)
S,
S
, V
S
in parallel with the inductor, eliminating the
FIGURE 9 — Sensor Gain
1/R
Current
CS
Desired Resistor
Sense
can be made to reach the comparator
S
R
C
S
L
S
2.5m
Value
5m
R
L
/L
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
V
CS
R
L
U S I N G T H E L X 1 6 6 0 / 6 1 D E V I C E S
R
C
S2
S
P
2.5 x 22
2.5 x 43
L
A
Dimensions (w x l)
, which causes a DC
mm
R O D U C T I O N
D V A N C E D
0.1 x 0.85
0.1 x 1.7
inches
Load
P W M C
S
,
D
CURRENT LIMIT
The dc/static tripping current I
than the static one. The dynamic tripping current I
General Guidelines for Selecting R
pendency of the inductance. Typical values are: R
9k , C
be lower than the desired short-circuit current limit, a resistor (R
can be put in parallel with C
of components is as follows:
C4 ERROR COMPARATOR INPUT BYPASS CAPACITOR
The LX1660/61 device has a unique topology which results in
extremely fast response to transient disturbances. Actual loop
closure is around a comparator. A capacitor should be placed
between the INV and NINV Error Comparator inputs to eliminate
jitter and noise. This capacitor value should be: C = ½ C
C
tion Information section.
C7 HICCUP CAPACITOR SELECTION
The hiccup capacitor controls two time periods; the ON time
duration of 10% duty cycle mode, and the OFF-time duration
before re-try. The ON:OFF-time ratios will always be 1:10 due to
the current sources which charge (10I) and discharge (I) the
hiccup capacitor. Select C
A T A
T
Select L/R
and C
The above equation has taken into account the current-de-
In cases where R
Again, select (R
is the timing capacitor. Refer to Capacitor C4 in the Applica-
Duration of reduced D operation = 100ms/µF
O N T R O L L E R
I
I
R
C
trip,S
trip,d
S
L
R
S
R
=
= 0.1µF, and L is 2.5µH at 0A current.
L (Required)
=
S
L (Actual)
S
=
=
according to:
R
I
V
trip,S
L (Actual)
H E E T
S
L/(R
trip
C
V
R
S
trip
V
L
(continued)
trip
S
C
S2
=
R
S
L
* (R
)
//R
L
L
is so large that the trip point current would
R
to have higher dynamic tripping current
S2
S
) < 10k .
S2
R
+ R
S2
// R
HICCUP
S
Select: R
C
, as shown in Figure 8. The selection
S
S n
S
)
trip,S
=
by using:
=
satisfies:
R
S
L
L
R
S
, C
n
R
L (Actual)
S
S
L
10 k
, and R
*
L
R
R
L
S
S2
trip,d
= 3m , R
+ R
* R
Copyright © 1998
satisfies:
T
Rev. 1.1a 10/25/2004
S2
S
, where
S
S2
=
)