參數(shù)資料
型號: LTC1708EG-PG
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: Dual Adjustable 5-Bit VID High Efficiency, 2-Phase Current Mode Synchronous Buck Regulator Controller
中文描述: 3 A DUAL SWITCHING CONTROLLER, 310 kHz SWITCHING FREQ-MAX, PDSO36
封裝: 0.209 INCH, PLASTIC, SSOP-36
文件頁數(shù): 25/32頁
文件大?。?/td> 358K
代理商: LTC1708EG-PG
25
LTC1708-PG
give a sense of the overall loop stability without breaking
the feedback loop. The initial output voltage step resulting
from the step change in output current may not be within
the bandwidth of the feedback loop, so this signal cannot
be used to determine phase margin. This is why it is better
to look at the I
TH
pin signal which is in the feedback loop
and is the filtered and compensated control loop re-
sponse. The gain of the loop will be increased by increas-
ing R
C
and the bandwidth of the loop will be increased by
decreasing C
C
. If R
C
is increased by the same factor that
C
C
is decreased, the zero frequency will be kept the same,
thereby keeping the phase the same in the most critical
frequency range of the feedback loop. The output voltage
settling behavior is related to the stability of the closed-
loop system and will demonstrate the actual overall supply
performance.
A second, more severe transient is caused by switching in
loads with large (>1
μ
F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C
OUT
, causing a rapid drop in V
OUT
. No regulator can
alter its delivery of current quickly enough to prevent this
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
C
LOAD
to C
OUT
is greater than1:50, the switch rise time
should be controlled so that the load rise time is limited to
approximately 25 C
LOAD
. Thus a 10
μ
F capacitor would
require a 250
μ
s rise time, limiting the charging current to
about 200mA.
APPLICATIU
W
U
U
Figure 9. Automotive Application Protection
Automotive Considerations: Plugging into the
Cigarette Lighter
As battery-powered devices go mobile, there is a natural
interest in plugging into the cigarette lighter in order to
conserve or even recharge battery packs during opera-
tion. But before you connect, be advised: you are plug-
ging into the supply from hell. The main power line in an
automobile is the source of a number of nasty potential
transients, including load-dump, reverse-battery and
double-battery.
Load-dump is the result of a loose battery cable. When the
cable breaks connection, the field collapse in the alternator
can cause a positive spike as high as 60V which takes
several hundred milliseconds to decay. Reverse-battery is
just what it says, while double-battery is a consequence of
tow-truck operators finding that a 24V jump start cranks
cold engines faster than 12V.
The network shown in Figure 9 is the most straight forward
approach to protect a DC/DC converter from the ravages
of an automotive power line. The series diode prevents
current from flowing during reverse-battery, while the
transient suppressor clamps the input voltage during
load-dump. Note that the transient suppressor should not
conduct during double-battery operation, but must still
clamp the input voltage below breakdown of the converter.
Although the LTC1708 has a maximum input voltage of
36V, most applications will be limited to 30V by the
MOSFET BVDSS.
V
IN
LTC1708-PG
T VOLTAGE
OR
NSTRUMENT
A I
PK
RATING
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