TL5001

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

7 of 13

www.unisonic.com.tw

QW-R103-016.E

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DETAILED DESCRIPTION(Cont.)

DEAD TIME CONTORL (DTC)

DTC provides a means of limiting the output-switch duty cycle to a value less than 100%, which is critical for boost

and flyback converters. A current source generates a reference current (IDT) at DTC that is nominally equal to the

current at the oscillator timing terminal, RT. Connecting a resistor between DTC and GND generates a dead-time

reference voltage (VDT), which the PWM/DTC comparator compares to the oscillator triangle wave as described in

the previous section. Nominally, the maximum duty cycle is 0% when VDT is 0.7V or less and 100% when VDT is

1.3V or greater. Because the triangle wave amplitude is a function of frequency and the source impedance of RT is

relatively high(1250Ω),choosing RDT for a specific maximum duty cycle, D, is accomplished using the following

maximum and minimum oscillator levels):

Where

start, the voltage at DTC is derived by the following equation:

UTC

TL5001

DTC

6

Fig. 2 Soft- Start Circuit

If the dc-to-dc converter must be in regulation within a specified period of time, the time constant, RDTCDT,

should be t0/3 to t0/5.The UTC TL5001 remains off unit VDT≈0.7V, the minimum ramp value. CDT 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 3V at 25℃) for proper operation. A hysteresis voltage of 200mV eliminates

false triggering on noise and chattering.