HV9150 Ver la hoja de datos (PDF) - Supertex Inc
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HV9150 Datasheet PDF : 15 Pages
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Design Procedure
There are several parameters that a user will decide for
the DC/DC converter design. The input voltage, output
voltage and output power requirement are usually defined
at the beginning. The few parameters that the user needs
to decide on include: operating frequency, inductor value,
duty cycle and the ON-resistance of the MOSFET. There
is some degree of flexibility in deciding the values of these
parameters. The following provides the user a general
approach to this subject.
Step 1
Since this DC/DC controller device is operating in a
discontinuous conduction mode, the following equations
are used to determine the inductance and the switching
frequency.
Given:
D = duty cycle
R = load resistance of the high voltage output
Vi = minimum input voltage
VO = output voltage
Unknown:
L = inductance
fGATE = driver switching frequency
where:
( VO =
Vi •
2
1+
4D2
1+
K
K
=
2
•
L•
R
fGATE
The maximum duty cycle can be determined by the following
equation:
DMAX
=
1
-
Vi
Vo
Then, the user can choose any duty cycle less than DMAX. It
is recommended that the largest possible setting be chosen.
To compensate for the limited efficiency, the user can add
the efficiency factor into the load resistance R. With the
above equation, the product of L and fGATE is determined.
The design will be limited by the product of L and fGATE.
HV9150
switching frequency can be computed. The required RFREQ
resistance can be found in the fGATE vs RFREQ table. Next,
the peak current of the inductor is checked by the following
equation. The saturation current of the inductor must be
larger than IPEAK.
IPEAK =
Vi • D
L • fGATE
Step 3
The most important factors to determine the MOSFET are
the breakdown voltage, the current capability, the ON-
resistance, the minimum VGS threshold voltage and the input
capacitance.
The HV9150 gate driver is designed to drive a maximum of
300pF capacitive load. So, the maximum input capacitance
of the external MOSFET should be less than 300pF. The
minimum breakdown voltage must be larger than the
required DC/DC converter output voltage. If the breakdown
voltage is too low, the output will never reach the required
voltage output. A MOSFET with high ON-resistance will limit
the peak current charging the inductor. The user can use
a simple RL charging circuit equation to determine its final
charging current.
( V
IL
=
i
RON
1 - exp
-
D
•
fGATE
RON
L
It is recommended that the calculated value of IL is within
95% of the IPEAK calculated in step 2. An ON-resistance of
less than 1Ω is usually a good starting point.
If the final circuit is short on the output current capability,
there are a few ways to boost the output. The user can do
any or all of the following to improve the output:
(1) increase the duty cycle
(2) decrease the fGATE
(3) use a MOSFET with lower ON-resistance.
Step 2
The standard inductor is usually sold in an incremental
inductance value, for example, 10, 22, 33 or 47µH. The user
can choose the inductance based on the size of the inductor,
the peak current, the maximum operating frequency and the
DC resistance. After the value of L is decided, the gate driver
Doc.# DSFP-HV9150
NR031914
Supertex inc.
8
www.supertex.com
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