TL1454CPW Datasheet, PDF (5/25 Pages) Texas Instruments – DUAL-CHANNEL PULSE-WIDTH-MODULATION (PWM) CONTROL CIRCUIT

TL1454, TL1454Y
DUAL-CHANNEL PULSE-WIDTH-MODULATION (PWM)
CONTROL CIRCUIT
SLVS086B – APRIL 1995 – REVISED NOVEMBER 1997
error amplifier
R1 and R2 should be tight-tolerance (±1% or better) devices with low and/or matched temperature coefficients
to minimize output voltage errors. A device with a ±5% tolerance is suitable for R3.
R2
R1
Converter
Output
VO
Compensation
Network
R3
REF
COMP
IN – _{_}
IN + ₊
To PWM
Figure 2. Sense Divider/Error Amplifier Configuration for Converters with Negative Outputs
Figure 2 shows the divider network and error-amplifier configuration for negative output voltages. In general,
the comments for positive output voltages also apply for negative outputs. The output voltage is given by:
+ * VO
R1Vref
R2
The design procedure for choosing the resistor value is to select a convenient value for R2 (instead of R3 in
the procedure for positive outputs) and calculate R1 and R3 using:
+ * R1
R2VO
Vref
+ ₎ R3
R1R2
R1 R2
Values in the 10-kΩ to 20-kΩ range work well for R2. R3 can be omitted and the noninverting amplifier connected
to ground in applications where the output voltage tolerance is not critical.
oscillator
The oscillator frequency can be set between 50 kHz and 2 MHz with a resistor connected between RT and GND
and a capacitor between CT and GND (see Figure 3). Figure 6 is used to determine R_T and C_T for the desired
operating frequency. Both components should be tight-tolerance, temperature-stable devices to minimize
frequency deviation. A 1% metal-film resistor is recommended for R_T, and a 10%, or better, NPO ceramic
capacitor is recommended for C_T.
TL1454
RT
CT
2
RT
1
CT
Figure 3. Oscillator Timing
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