LA5754MP

No.A0952-4/5

Td =

=

= 28.2 msec

C

× V

i

1

µ × 0.62

22

µ

Tss =

=

C

× ∆VPWM × PWMduty

i

C

× 0.88 × PWMduty

22

µA

1.5V

0.62V

PWM wave

PWMduty =

= 25%

VOUT + VF

VIN - Vsat + VF

Tss =

= 10msec

1

µ × 0.88V × 0.25

22

µA

Description of Functional Settings

1.Start delay function

The SS pin has the internally-connected 22

µA (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 1

µF

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.

(Note that calculation is made with Vsat = 1V and VF = 0.2V)

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:

For the set conditions of C = 1

µF and PWMduty = 25%: