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TPS65136RTE Datasheet(PDF) 10 Page - Texas Instruments |
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TPS65136RTE Datasheet(HTML) 10 Page - Texas Instruments |
10 / 21 page Advanced Power-Save Mode for Light-Load Efficiency Buck-Boost Mode Operation Inherent Excellent Line-Transient Regulation I p t clock A A pos neg V V L + in V L M0116-01 o outp outn V = V + V o in o V D = V V h + g TPS65136 SLVS831A – APRIL 2008 – REVISED JULY 2008 ............................................................................................................................................................. www.ti.com In order to maintain high efficiency over the entire load-current range, the converter reduces its switching frequency as the load current decreases. The advanced power-save mode controls the switching frequency using a voltage-controlled oscillator (VCO). The VCO frequency is proportional to the inductor peak current, with a lower frequency limit of 20 kHz. This avoids disturbance of the audio band and minimizes audible noise coming from the ceramic input and output capacitors. By maintaining a controlled switching frequency, possible EMI is minimized. This is especially important when using the device in mobile phones. See Figure 8 for typical switching frequency versus load current. Buck-boost mode operation allows the input voltage to be higher than the output voltage. This mode allows the use of batteries and supply voltages that are above the fixed 4.6-V output voltage of OUTP. The SIMO regulator achieves inherent superior line-transient regulation when operating in discontinuous conduction mode, shown in Figure 5 and Figure 6. In discontinuous conduction mode, the current delivered to the output is given by the inductor peak current and falling slope of the inductor current. This is shown in Figure 14, where the output current, given by the area A, is the same for different input voltages. Because the converter uses peak-current-mode control, the peak current is fixed as long as the load current is fixed. The falling slope of the inductor current is given by the sum of the output voltage and inductor value. This is also a fixed value and independent of the input voltage. Because of this, any change in input voltage changes the converter duty cycle but does not change the inductor peak current or the falling slope of the inductor current. Therefore, the output current, given by the area A (Figure 14), remains constant over any input voltage variation. Because the area A is constant, the converter has an inherently perfect line regulation when operating in discontinuous conduction mode. Entering continuous conduction mode (CCM) linearly decreases the line-transient performance. However, the line-transient response in CCM is still as good as for any standard current-mode-controlled switching converter. The following formulas detail the relations of the TPS65136 converter topology operating in CCM. Figure 14. Inherently Perfect Line-Transient Regulation The converter always sees the sum of the negative and positive output voltage, which is calculated as: The converter duty cycle is calculated using the efficiency estimation from the data sheet curves or from real application measurements. A 70% efficiency value is a good value to go through the calculations. The output current for entering continuous conduction mode can be calculated. The switching frequency can be obtained from the data sheet graphs. A frequency of 1.5 MHz is usually sufficient for these types of calculations. 10 Submit Documentation Feedback Copyright © 2008, Texas Instruments Incorporated Product Folder Link(s): TPS65136 |
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