www.德州仪器.com
APPLICATIONINFORMATION
adjustingtheoutputvoltageoftheptn78000awide-outputadjustpowermodules
一般
R = 54.9 k
设置
1
.
2
5
V
| |
V - 3 v
O
- 5.62 k
InputVoltageConsiderations
地
V
O
PTN78000A
1
5
2
Adj
地
V
O
V
I
V
I
地
4
+
+
C1
C2
R
S
E
T
0.05 w
1%
C3
PTN78000A
SLTS246A–APRIL2005–REVISEDMAY2005
Aresistormustbeconnecteddirectlybetweenthe
V
O
调整
控制(pin4)andtheoutput
电压
(pin7)toset
theoutputvoltagelowerthan–3v.theadjustmentrangeisfrom–15vto–3v.ifpin4isleftopen,theoutput
voltagedefaultstothehighestvalue,–3v.
Table1givesthestandardresistorvalueforanumberofcommonvoltages,andwiththeactualoutputvoltage
thatthevalueproduces.forotheroutputvoltages,theresistorvaluecaneitherbecalculatedusingthefollowing
formula,orsimplyselectedfromtherangeofvaluesgiveninTable2.Figure17showstheplacementofthe
requiredresistor.
theptn78000aisabuck-boostswitchingregulator.inorderthattheoutputremainsinregulation,theinput
voltagemustnotexceedtheoutputbyamaximumdifferentialvoltage.
forsatisfactoryperformance,themaximumoperatinginputvoltageis(32-|v
O
|)伏特.
asanexample,Table1givestheoperatinginputvoltagerangeforthecommonoutputbusvoltages.inaddition,
theelectricalcharacteristicsdefinetheavailableoutputvoltageadjustrangeforvariousinputvoltages.
table1.standardvaluesofr
设置
forCommonOutput
电压
V
O
R
设置
V
O
运行
(必需的)(standardvalue)(真实的)v
I
范围
–15V100
Ω
–14.997v9vto17v
–12V2k
Ω
–12.006v9vto20v
–5v28.7k
Ω
–5.000v9vto27v
–3.3v221k
Ω
–3.303v9vto28.7v
(1)a0.05-wratedresistormaybeused.thetoleranceshouldbe1%,withatemperaturestabilityof100ppm/°c(或者
更好的).placetheresistorasclosetotheregulatoraspossible.connecttheresistordirectlybetweenpins4and1
usingdedicatedpcbtraces.
(2)neverconnectcapacitorsfrom
V
O
调整
toeither
地
或者
V
O
.anycapacitanceaddedtothe
V
O
调整
pinaffectsthe
stabilityoftheregulator.
figure17.v
O
AdjustResistorPlacement
8
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