MC33253 查看數據表（PDF） - Motorola => Freescale
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MC33253 Datasheet PDF : 15 Pages
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MC33253
The smaller Ccp value is, the smaller Vcp_out value is. Moreover, for a same Ccp value, when the switching frequency
increases, the average Vcp_out level decreases. For most of the applications a typical value of 33nF is recommended.
Ccp_out
As shown in figure 11, at high side MOSFET turn on, Vcp_out voltage decreases. This decrease can be calculated according to
Ccp_out value as following :
Qg : Power MosFET Gate Charge
∆VCcp _ out
=
Qg
Ccp _ out
The following figure is the simplified Ccp_out current and voltage waveforms.
fpwm : working switching frequency
Figure 11. Simplified Ccp_out Current and Voltage Waveforms
VCp_out
average VCp_out
Oscillator
in high
state Oscillator
in low
state
High Side
turn on
∆VCcp _ out
ICp_out
f=330kHz
fPWM
Peak
Current
CLR_OUT
CLR_OUT provides peak current needed by the low side MOSFET turn on. VLR_OUT decreasing is as follow:
∆VLR _ out
=
Qg
CLR _ out
Capacitors typical values
In most working cases the following typical values are advised for a good charge pump performing:
Ccp=33nF, Ccp_out=470nF and CLR_OUT=470nF.
These values give a typical 100mV voltage ripple on Vcp_out and VLR_OUT with Qg=50nC.
OP-Amp
The built-in A.O.P. available in the MC33253 allows to get a voltage image of the H-bridge current. This voltage can be
provided by a shunt resistor, as shown in figure 13.
Typically shunt resistivity is dimensioned as low as possible (25mOhm/10A). The maximum A.O.P output voltage is 5V.
Therefore a gain of 10 sets the maximum drop voltage on the sensing resistance at 500mV.
MC33253
MOTOROLA
rev3.0 - 11/15
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