TL5001A-Q1_15 Datasheet, PDF (4/19 Pages) Texas Instruments – PULSE-WIDTH-MODULATION CONTROL CIRCUITS

TL5001A-Q1
SLVS603B – AUGUST 2005 – REVISED FEBRUARY 2009 .............................................................................................................................................. www.ti.com
Soft start can be implemented by paralleling the DTC resistor with a capacitor (C_DT) as shown in Figure 2. During
soft start, the voltage at DTC is derived by the following equation:
ǒ Ǔ VDT [ IDTRDT 1 * e*RDTtCDT
(2)
6 _DTC
TL5001/A
C_DT
R_DT
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 TL5001A 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 TL5001A 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.
2.5 V
R_SCP 185 kΩ
C_SCP
5
SCP
From Error
Amp
1.5 V
SCP
Comparator 1
Q2
12 kΩ
SCP
Comparator 2
Q1
V_ref = 1 V
To Output
Drive Logic
Figure 3. SCP Circuit
4
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