M62281P Datasheet, PDF (8/13 Pages) Mitsubishi Electric Semiconductor – GENERAL PURPOSE CURRENT MODE PWM CONTROL IC

M62281P/FP
SOFT (Duty Set-Up) Terminal
The voltage of SOFT terminal determines the maximum duty.
Maximum duty can be set by connecting the resistor as in figure 6 because the constant current compensated for
temperature flows out of this terminal.
And by connecting the capacitor between the terminal and GND, soft start function operates. That is, we can get the
gradual increase of maximum duty at start-up.
SOFT
C_SOFT ⁺
V_SOFT
Figure 6 Method to Set Up Duty and SOFT Start Function
Maximum duty is represented as :
Duty (Max.) ≈ (42 • V_SOFT) − 59 (%)
where V_SOFT = I_SOFT • R_SOFT (V), I_SOFT = 43 µA (Typ.)
If the voltage of SOFT terminal is higher than 3.53 V (Typ.) (upper limit voltage of the oscillation waveform),
maximum duty is internally decided to be 90%.
Soft start time (T_SOFT) is represented as :
T_SOFT ≈ C_SOFT • 31 • 10³ (s)
T_SOFT means the time from start-up until the voltage of SOFT terminal goes up to higher than 1.4 V (Typ.) (lower limit
voltage of the oscillation waveform).
Discharging circuit operative before start-up at V_CC is internally equipped so that the soft start never fail to operate at
the restart of voltage supply.
CLM Terminal
This terminal is for pulse-by-pulse current limiting.
Current limiting circuit is almost the same as that of M51995.
CLM terminal is separate from CURRENT SENSE terminal allowing the noise filter to be optimized and the high-
speed over current protection.
The voltage detected by the current detecting resistor can be directly input as shown in figure 7-1, if the detected
voltage is about the threshold voltage (200 mV (Typ.)), but if the voltage is larger than the threshold, the voltage has to
be input divided by resistors as shown in figure 7-2.
CLM OUT
R_NF
C_NF
R_CS
Figure 7-1 Peripheral Circuit of CLM
REJ03D0840-0201 Rev.2.01 Nov 14, 2007
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