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TL5001_16 Datasheet, PDF (5/32 Pages) Texas Instruments – PULSE-WIDTH-MODULATION CONTROL CIRCUITS
TL5001, TL5001A
PULSE-WIDTH-MODULATION CONTROL CIRCUITS
short-circuit protection (SCP) (continued)
SLVS084F – APRIL 1994 – REVISED JANUARY 2002
2.5 V
RSCP 185 kΩ
CSCP
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SCP
From Error
Amp
1.5 V
SCP
Comparator 1
Q2
12 kΩ
SCP
Comparator 2
Q1
Vref = 1 V
To Output
Drive Logic
Figure 3. SCP Circuit
The timer operates by charging an external capacitor (CSCP), connected between the SCP terminal and ground,
towards 2.5 V through a 185-kΩ resistor (RSCP). 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 the following
+ * ǒ * ń Ǔ ) equation:
VSCP (2.5 0.185) 1 e–t t
0.185
Where
τ = RSCPCSCP
The end of the time-out period, tSCP, occurs when VSCP = 1 V. Solving for CSCP yields:
+ CSCP 12.46 tSCP
Where
t is in seconds, C in µF.
tSCP 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 TL5001/A 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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