TL5001_15 Datasheet, PDF (6/13 Pages) Unisonic Technologies – PULSE-WIDTH-MODULATION CONTROL CIRCUIT

TL5001
LINEAR INTEGRATED CIRCUIT
 DETAILED DESCRIPTION
VOLTAGE REFERENCE
A 2.5-V regulator operating from V_CC is used to power the internal circuitry of the TL5001 and as a reference for
the error amplifier and SCP circuit. A resistive divider provides a 1-V reference for the error amplifier non-inverting
input which typically is within 2% of nominal over the operating temperature range.
ERROR AMPLIFIER
The error amplifier compares a sample of the dc-to-dc converter output voltage to the 1-V reference and generates
an error signal for the PWM comparator. The dc-to-dc converter output voltage is set by selecting the error –amplifier
gain (see Fig. 1), using the following expression.
V_OUT = (1+R1/R2) (1V)
The error-amplifier output is brought out as COMP for use in compensating the dc-to-dc converter control loop for
stability. Because the amplifier can only source 45µA, the total dc load resistance should be 100kΩ or more.
OSCILLATOR/PWM
The oscillator frequency (f_OSC) can be set between 20kHz and 500kHz by connecting a resistor between RT and
GND .Acceptable resistor values range from 15 kΩ to 250 kΩ. The oscillator frequency can be determined by using
the graph shown in Fig. 5.
The oscillator output is a triangular wave with a minimum value of approximately 0.7V and a maximum value of
approximately 1.3V. The PWM comparator compares the error-amplifier output voltage and the DTC input voltage to
the triangular wave and turns the output transistor off whenever the triangular wave is greater than the lesser of the
two inputs.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R103-016.E