TL5001A-Q1_15 Datasheet, PDF (5/19 Pages) Texas Instruments – PULSE-WIDTH-MODULATION CONTROL CIRCUITS

TL5001A-Q1
www.ti.com .............................................................................................................................................. SLVS603B – AUGUST 2005 – REVISED FEBRUARY 2009
The timer operates by charging an external capacitor (C_SCP) connected between the SCP terminal and ground,
towards 2.5 V through a 185-kΩ resistor (R_SCP). The circuit begins charging from an initial voltage of
approximately 185 mV and times out when the capacitor voltage reaches 1 V. The output of SCP comparator 2
then goes high, turns on Q2, and latches the timer circuit. The expression for setting the SCP time period is
derived from Equation 3:
V_SCP = (2.5 – 0.185) (1 – e^–t/τ) + 0.185
(3)
Where
τ = R_SCPC_SCP
The end of the time-out period (t_SCP) occurs when V_SCP = 1 V. Solving for C_SCP yields Equation 4:
C_SCP = 12.46 × t_SCP
(4)
Where
t is in seconds, C is in µF
t_SCP must be much longer (generally 10 to 15 times) than the converter start-up period, or the converter will not
start.
OUTPUT TRANSISTOR
The output of the TL5001A is an open-collector transistor with a maximum collector current rating of 21 mA and a
voltage rating of 51 V. The output is turned on under the following conditions: the oscillator triangle wave is lower
than both the DTC voltage and the error-amplifier output voltage, the UVLO circuit is inactive, and the
short-circuit protection circuit is inactive.
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