TL5001 Datasheet, PDF (5/23 Pages) Texas Instruments – PULSE-WIDTH-MODULATION CONTROL CIRCUITS

TL5001, TL5001A
PULSE-WIDTH-MODULATION CONTROL CIRCUITS
short-circuit protection (SCP) (continued)
SLVS084E – APRIL 1994 – REVISED OCTOBER 1999
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 (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
+ * ǒ * ń Ǔ ) derived from the following equation:
VSCP (2.5 0.185) 1 e–t ^t
0.185
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:
+ 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.
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