Datasheet

TL5001, TL5001A
PULSE-WIDTH-MODULATION CONTROL CIRCUITS
SLVS084F – APRIL 1994 – REVISED JANUARY 2002
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
short-circuit protection (SCP) (continued)
Q1
12 kΩ
185 kΩ
R
SCP
Q2
SCP
Comparator 2
V
ref
= 1 V
SCP
Comparator 1
1.5 V
From Error
Amp
C
SCP
To Output
Drive Logic
SCP
5
2.5 V
Figure 3. SCP Circuit
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 the following
equation:
V
SCP
(
2.5 0.185
)
1 e
–t
0.185
Where
τ = R
SCP
C
SCP
The end of the time-out period, t
SCP
, occurs when V
SCP
= 1 V. Solving for C
SCP
yields:
C
SCP
12.46 t
SCP
Where
t is in seconds, C 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 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.