TL5001

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 13

www.unisonic.com.tw

QW-R103-016,B

DETAILED DESCRIPTION

VOLTAGE REFERENCE

A 2.5-V regulator operating from Vcc 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 Figure 1), using the following expression.

+

-

FB

COMP

GND

R1

R2

To PWM

Comparator

Compensation

Network

3

4

8

Figure 1.Error-Amplifier Gain Setting

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 (fosc) 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 Figure 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.