Datasheet

V
DT
[ I
DT
R
DT
ǒ
1 * e
*
t
R
DT
C
DT
Ǔ
(2)
TL5001/A
DTC
C
DT
R
DT
6
UNDERVOLTAGE-LOCKOUT (UVLO) PROTECTION
SHORT-CIRCUIT PROTECTION (SCP)
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
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:
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
DT
C
DT
) should
be t
0
/3 to t
0
/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.
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.
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.
Figure 3. SCP Circuit
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Product Folder Link(s): TL5001A-Q1