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HT7991 Datasheet(PDF) 9 Page - Holtek Semiconductor Inc

Part # HT7991
Description  Asynchronous Step-up PWM Converter
PDF  13 Pages
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Manufacturer  HOLTEK [Holtek Semiconductor Inc]
Direct Link  http://www.holtek.com
Logo HOLTEK - Holtek Semiconductor Inc

HT7991 Datasheet(HTML) 9 Page - Holtek Semiconductor Inc

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Rev. 1.20
9
June 01, 2017
HT7991
Component Selection Guide
Inductor
The selected inductor should have a saturation
currentthatmeetsthemaximumpeakcurrentofthe
converter.Anotherimportantinductorparameteris
thedcresistance.Thelowerthedcresistancegains
thehighertheefficiencyoftheconverter.Formost
applications,theinductorvaluecanbecalculated
fromthefollowingequation:
L=()×
Vin 2 (Vout−Vin)
Iripple×fsw
Vout
Thehighervalueofripplecurrentreducesinductance,
buttheconductanceloss,coreloss,andcurrentstress
oftheinductorandswitchingdevicesincrease.It’s
suggestedthatchoosingtheinductorripplecurrentto
be30%ofthemaximumloadcurrent.
Diode
Thebreakdownvoltageratingofthediodeispreferred
tobehigherthanthemaximuminputvoltage.The
currentratingforthediodeshouldbeequaltothe
maximumoutputcurrentforbestreliabilityinmost
applications.Inthiscase,itispossibletouseadiode
withaloweraveragecurrent.Howeverthepeak
currentshouldbehigherthanthemaximumload
current.
Input Capacitor
AlowESRceramiccapacitorisneededbetweenthe
VINpinandGNDpin.Useceramiccapacitorswith
X5RorX7RdielectricsforitslowESRandsmall
temperaturecoefficients.Formostapplications,the
capacitanceintherangeof2.2μFto10μFcapacitoris
sufficient.
Output Capacitor
Theselectionofoutputcapacitorisdrivenbythe
maximumallowableoutputvoltageripple.Using
ceramiccapacitorswithX5RorX7Rdielectricsforits
lowESRcharacteristicissuggested.Thecapacitance
intherangeof10μFto100μFissufficient.
Recommended Component Values
VOUT
R3
L1
D1
C1
47µF
C2
0.1µF
OFF
ON
VIN
R1
R2
VIN
EN
OC
LX
FB
GND
5
4
6
1
3
2
HT7991
C3
47µF
C4
0.1µF
VOUT (V)
R1 (kΩ)
R2 (kΩ)
C3 (μF)
C4 (μF)
L1 (μH)
5.1
75 (1%)
10 (1%)
47
0.1
3.3
12.0
190 (1%)
10 (1%)
47
0.1
6.8



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