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LA5751 View Datasheet(PDF) - SANYO -> Panasonic

Part Name
Description
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LA5751 Datasheet PDF : 5 Pages
1 2 3 4 5
LA5751
Description of Functional Settings
1.Start delay function
The SS pin has the internally-connected 22µA (typ) constant-current supply. When the voltage of SS pin exceeds the
threshold voltage, the regulator starts operation. As the threshold is 0.62V(typ), the start delay time can be calculated
as follows:
ex. For setting at 1µF
Td
=
C
×
i
V
=
1µ
× 0.62
22µ
=
28.2
msec
2.Soft start function
The internal PWM waveform has the voltage value as shown in the right.
If down-conversion from the voltage of VIN = 15V to 3.3V output to be made,
for example, the PWM-ON duty has the value as shown below.
PWMduty
=
VOUT +
VIN - Vsat
VF
+ VF
= 25%
(Note that calculation is made with Vsat = 1V and VF = 0.2V)
1.5V
0.62V
PWM wave
The output voltage of error amplifier, which is 3.3V, is the value with PWM = 25%, as calculated in the above
equation, so that this voltage is determined as follows:
Ver = (VPWM) × PWMduty + VPWML = 0.88V × 0.25 + 0.62V = 0.84V
(VPWM is the PWM amplitude value or 0.88V(typ) while VPWML is the lower limit voltage of PWM
waveform or 0.62V(typ))
SS pin and error amplifier output voltages are designed to prefer the lower voltages, so that VOUT will reach the
designed regulation voltage in timing when the SS pin voltage exceeds the error amplifier output. Therefore, the soft
strt time is calculated as follows:
Tss
=C
×
VPWM ×
i
PWMduty
=
C
×
0.88 × PWMduty
22µA
For the set conditions of C = 1µF and PWMduty = 25%:
Tss
=
1µ
×
0.88V ×
22µA
0.25
=
10msec
No.A0945-4/5
 

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