L5988D View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L5988D
STMicroelectronics
'L5988D' PDF : 52 Pages View PDF
Application information
L5988D
have to be chosen in order to sustain load transient and to have a fast response to the
transient.
In Table 13 some capacitor series are listed.
Manufacturer
MURATA
PANASONIC
SANYO
TDK
Table 13. Output capacitors
Series
Cap value (F) Rated voltage (V)
GRM32
22 to 100
6.3 to 25
GRM31
10 to 47
6.3 to 25
ECJ
10 to 22
6.3
EEFCD
10 to 68
6.3
TPA/B/C
100 to 470
4 to 16
C3225
22 to 100
6.3
ESR (m)
<5
<5
<5
15 to 55
40 to 80
<5
6.4
Compensation network
The compensation network has to assure stability and good dynamic performance. The loop
of the L5988D is based on the voltage mode control. The error amplifier is a voltage
operational amplifier with high bandwidth. So selecting the compensation network the E/A
will be considered as ideal, that is, its bandwidth is much larger than the system one.
The transfer functions of PWM modulator and the output LC filter are studied. The transfer
function PWM modulator, from the error amplifier output (COMP pin) to the OUT pin, results:
Equation 20
GPW0fSW0 = -V-V---I-sN-- HfSW0
where VS is the sawtooth amplitude and H represent its reliance on the switching frequency.
As seen in Section 5.2 on page 15, the voltage feed forward generates a sawtooth
amplitude directly proportional to the input voltage, that is:
Equation 21
VSfSW0 = K VIN HfSW0
The internal saw tooth is designed in order to have the maximum amplitude at the natural
switching frequency of the device.
At fSW0 = 400 kHz the PWM modulator can be written as:
Equation 22
GPW0400 kHz = K-1-- = -V----S------4--V-0---0-I-N----k---H----z---- = 9
The synchronization of the device with an external clock fed into the SYNCH pin and the
adjustment of the switching frequency through the FSW pin modify the gain of the internal
saw tooth (see Section 5.2 on page 15).
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