参数资料
型号: LT1506CR-SYNC#PBF
厂商: Linear Technology
文件页数: 21/24页
文件大小: 0K
描述: IC REG BUCK ADJ 4.5A D2PAK
标准包装: 50
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 可调
输入电压: 4 V ~ 15 V
PWM 型: 电流模式
频率 - 开关: 500kHz
电流 - 输出: 4.5A
同步整流器:
工作温度: 0°C ~ 125°C
安装类型: 表面贴装
封装/外壳: TO-263-8,D²Pak(7 引线+接片),TO-263CA
包装: 管件
供应商设备封装: D2PAK-7
LT1506
APPLICATIO N S I N FOR M ATIO N
RIPPLE FILTER
SWITCHING
REGULATOR
+
100 μ F TO
1000 μ F
470 ?
3300pF
4.7k
330pF
TO X1
OSCILLOSCOPE
PROBE
ADJUSTABLE
INPUT SUPPLY
ADJUSTABLE
DC LOAD
50 ?
TO
OSCILLOSCOPE
SYNC
100Hz TO 1kHz
100mV TO 1V P-P
1506 F13
Figure 13. Loop Stability Test Circuit
Keep in mind that this procedure does not take initial
V OUT AT I OUT =
500mA
BEFORE FILTER
V OUT AT I OUT =
component tolerance into account. You should see fairly
clean response under all load and line conditions to ensure
that component variations will not cause problems. One
10mV/DIV
5A/DIV
0.2ms/DIV
1375/76 F14
500mA
AFTER FILTER
V OUT AT I OUT = 50mA
AFTER FILTER
LOAD PULSE
THROUGH 50 ?
f ≈ 780Hz
note here: according to Murphy, the component most
likely to be changed in production is the output capacitor,
because that is the component most likely to have manu-
facturer variations (in ESR) large enough to cause prob-
lems. It would be a wise move to lock down the sources of
the output capacitor in production.
Figure 14. Loop Stability Check
The output of the regulator contains both the desired low
frequency transient information and a reasonable amount
of high frequency (500kHz) ripple. The ripple makes it
difficult to observe the small transient, so a two-pole,
100kHz filter has been added. This filter is not particularly
critical; even if it attenuated the transient signal slightly,
this wouldn’t matter because amplitude is not critical.
After verifying that the setup is working correctly, I start
varying load current and input voltage to see if I can find
any combination that makes the transient response look
suspiciously “ringy.” This procedure may lead to an
adjustment for best loop stability or faster loop transient
response. Nearly always you will find that loop response
looks better if you add in several k ? for R C . Do this only
if necessary, because as explained before, R C above 1k
may require the addition of C F to control V C pin ripple. If
everything looks OK, I use a heat gun and cold spray on the
circuit (especially the output capacitor) to bring out any
temperature-dependent characteristics.
A possible exception to the “clean response” rule is at very
light loads, as evidenced in Figure 14 with I LOAD = 50mA.
Switching regulators tend to have dramatic shifts in loop
response at very light loads, mostly because the inductor
current becomes discontinuous. One common result is very
slow but stable characteristics. A second possibility is low
phase margin, as evidenced by ringing at the output with
transients. The good news is that the low phase margin at
light loads is not particularly sensitive to component varia-
tion, so if it looks reasonable under a transient test, it will
probably not be a problem in production. Note that fre-
quency of the light load ringing may vary with component
tolerance but phase margin generally hangs in there.
CURRENT SHARING MULTIPHASE SUPPLY
The circuit in Figure 15 uses multiple LT1506s to produce
a 5V, 12A power supply. There are several advantages to
using a multiple switcher approach compared to a single
larger switcher. The inductor size is considerably reduced.
Three 4A inductors store less energy (LI 2 /2) than one 12A
coil so are far smaller. In addition, synchronizing three
21
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