參數(shù)資料
型號: LX1663CDT
元件分類: 穩(wěn)壓器
英文描述: 1.5 A SWITCHING CONTROLLER, 200 kHz SWITCHING FREQ-MAX, PDSO16
封裝: PLASTIC, SOIC-16
文件頁數(shù): 5/15頁
文件大?。?/td> 308K
代理商: LX1663CDT
SINGLE-CHIP PROGRAMMABLE PWM CONTROLLERS WITH 5-BIT DAC
LX1662/62A, LX1663/63A
PRODUCT DA T ABOOK 1996/1997
13
Copyright 1999
Rev. 1.1 11/99
P RODUCTION D ATA S HEET
USING THE LX1662/63 DEVICES
CURRENT LIMIT (continued)
PCB Sense Resistor
A PCB sense resistor should be constructed as shown in Figure
10. By attaching directly to the large pads for the capacitor and
inductor, heat is dissipated efficiently by the larger copper masses.
Connect the current sense lines as shown to avoid any errors.
Copper
Desired Resistor
Dimensions (w x l)
Weight Thickness
Value
mm
inches
2 oz/ft2
68m
2.5m
2.5 x 22
0.1 x 0.85
5m
2.5 x 43
0.1 x 1.7
TABLE 3 - PCB Sense Resistor Selection Guide
Recommended sense resistor sizes are given in the following
table:
CURRENT LIMIT (continued)
The current flowing through the inductor is a triangle wave. If the
sensor components are selected such that:
L/R
L = RS * CS
The voltage across the capacitor will be equal to the current
flowing through the resistor, i.e.
V
CS = ILRL
Since V
CS
reflects the inductor current, by selecting the
appropriate R
S and CS, VCS can be made to reach the comparator
voltage (60mV for LX166xA or 100mV for the LX166x) 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:
Loss-Less Current Sensing Using Resistance of Inductor
Any inductor has a parasitic resistance, R
L, which causes a DC
voltage drop when current flows through the inductor. Figure 11
shows a sensor circuit comprising of a surface mount resistor, R
S,
and capacitor, C
S, in parallel with the inductor, eliminating the
current sense resistor.
2.5m
9 Sense Resistor
100mil Wide, 850mil Long
2.5mm x 22mm (2 oz/ft2 copper)
Output
Capacitor Pad
Inductor
Sense Lines
FIGURE 10 — Sense Resistor Construction Diagram
R
L
L/R
SCS
|T(
j M )|
M
1/R
SCS
R
L/L
FIGURE 12 — Sensor Gain
FIGURE 11 — Current Sense Circuit
R
L
R
S
C
S
V
CS
Current
Sense
Comparator
Load
R
S2
The dc/static tripping current I
trip,S satisfies:
I
trip,S =
Select L/R
SCS ≤ RL to have higher dynamic tripping current
than the static one. The dynamic tripping current I
trip,d satisfies:
I
trip,d =
General Guidelines for Selecting R
S , CS , and RL
R
L =
Select: R
S ≤ 10 k
and C
S according to:
C
Sn =
The above equation has taken into account the current-de-
pendency of the inductance.
The test circuit (Figure 6) used the following parameters:
R
L = 3m, RS = 9k, CS = 0.1F, and L is 2.5H at 0A current.
V
trip
L/(R
SCS)
V
trip
R
L
V
trip
I
trip,S
L
n
R
L RS
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