TL5001 Datasheet, PDF (4/23 Pages) Texas Instruments – PULSE-WIDTH-MODULATION CONTROL CIRCUITS

TL5001, TL5001A
PULSE-WIDTH-MODULATION CONTROL CIRCUITS
SLVS084E – APRIL 1994 – REVISED OCTOBER 1999
dead-time control (DTC) (continued)
+ ^ǒ ) ^{Ǔ ƪ ǒ Ǔ} ) ^ƫ RDT Rt 1250 D Voscmax – Voscmin Voscmin
Where
R_DT and R_t are in ohms, D in decimal
[ ǒ ^{ǒ ń Ǔ}Ǔ ^{Soft start can be implemented by paralleling the DTC resistor with a capacitor (CDT) as shown in Figure 2. During}
soft start, the voltage at DTC is derived by the following equation:
VDT IDTRDT 1– e ^{– t RDTCDT}
CDT
6 _DTC
TL5001/A
RDT
Figure 2. Soft-Start Circuit
If the dc-to-dc converter must be in regulation within a specified period of time, the time constant, R_DTC_DT,
should be t₀/3 to t₀/5. The TL5001/A remains off until V_DT ≈ 0.7 V, the minimum ramp value. C_DT is discharged
every time UVLO or SCP becomes active.
undervoltage-lockout (UVLO) protection
The undervoltage-lockout circuit turns the output transistor off and resets the SCP latch whenever the supply
voltage drops too low (approximately 3 V at 25°C) for proper operation. A hysteresis voltage of 200 mV
eliminates false triggering on noise and chattering.
short-circuit protection (SCP)
The TL5001/A includes short-circuit protection (see Figure 3), which turns the power switch off to prevent
damage when the converter output is shorted. When activated, the SCP prevents the switch from being turned
on until the internal latching circuit is reset. The circuit is reset by reducing the input voltage until UVLO becomes
active or until the SCP terminal is pulled to ground externally.
When a short circuit occurs, the error-amplifier output at COMP rises to increase the power-switch duty cycle
in an attempt to maintain the output voltage. SCP comparator 1 starts an RC timing circuit when COMP exceeds
1.5 V. If the short is removed and the error-amplifier output drops below 1.5 V before time out, normal converter
operation continues. If the fault is still present at the end of the time-out period, the timer sets the latching circuit
and turns off the TL5001/A output transistor.
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