Using TPS62200 as a dynamic voltage scaler for OMAP1510

It is no doubt that extending the battery life of portable electronic products will help to sell the products. For microprocessors, reducing the internal clock frequency and/or reducing the core voltage can help to reduce its power consumption. Dynamic voltage scaling (DVS) is a technique that is often used to reduce the core voltage to reduce power consumption. This article will explain how to use the TPS62200 buck converter to implement dynamic voltage scaling as a power supply for the OMAP1510 processor.

The following formula will explain how to calculate the power consumption of a microprocessor using the TI-DSP core:

PC~(VC)2×f Where PC represents the core power consumption, VC is the core voltage, and f is the core clock frequency.

Therefore, reducing the internal clock frequency and/or reducing the core voltage can reduce the core power consumption. Dynamic voltage scaling is a technique that is often used to reduce the core voltage to reduce the core power consumption. This article will explain how to use the TPS62200 buck converter to implement dynamic voltage scaling as a power supply for the OMAP1510 processor.

The OMAP1510 processor has two operating modes: AWAKE mode and low-power DEEP-SLEEP mode. In AWAKE mode, the OMAP1510 processor requires an input voltage of 1.5 volts. In DEEP-SLEEP mode, the OMAP1510 processor can operate at an input voltage of 1.1 or 1.5 volts. In DEEP-SLEEP mode, if the input voltage VDDx = 1.1 volts, the power consumption of the OMAP1510 processor will be minimized. Figure 1 shows a circuit diagram of dynamic voltage scaling technology using the TPS62200 adjustable buck converter. The figure also includes an additional feedback resistor RX and a digital control signal called Low Power Mode (LPM), which will turn to a low state when the voltage drops from 1.5 volts to 1.1 volts.

Figure 1: Using TPS62200 as a dynamic voltage scaler for OMAP1510.

The control signal LPM injects current into the feedback network through RX to change the output voltage. Equations 1 and 2 sum the currents at the feedback node VFB. Solving Equations 1 and 2 simultaneously and substituting them back to solve for RB yields Equations 3 and 4. These equations can be used to calculate the injection resistor RX and the bottom feedback resistor RB. In Figure 1, RT = 402kΩ, VO_HI = 1.5V, VO_LO = 1.1V, VLPM_HI = 2.8V, VLPM_LO = 0V, and VFB = 0.5V.

Figure 2 shows the output voltage transient when the load current drops to 300 microamperes. The reason the transient time is too long is because the discharge current used to discharge the 10μF output capacitor from 1.5 volts to 1.1 volts is only 300 microamperes. [page]

Figure 2: Transition between two output voltages.

The TPS62200 is well suited for implementing dynamic voltage scaling techniques. When the OMAP1510 operates in AWAKE mode, the TPS62200 operates in PWM mode to achieve high efficiency and deliver higher load currents. When the OMAP1510 operates in DEEP-SLEEP mode, the TPS62200 operates in PFM mode to more efficiently deliver lower load currents of hundreds of microamperes. For example, when using the TPS62200 and a 3.6V, 1Ah Li-Ion battery as the input power source for the OMAP1510 chip, the following characteristics can be achieved in this architecture:

1) DEEP-SLEEP mode without dynamic voltage scaling (TPS62200 operating in PFM mode): VO = 1.5V, 300μA, efficiency = 93%.

2) DEEP-SLEEP mode with dynamic voltage scaling (TPS62200 in PFM mode): VO = 1.1 volts, 250 μA, efficiency = 93%.

3) AWAKE mode: VO = 1.5 volts, 100 mA, efficiency = 96%. Assuming the microprocessor operates in AWAKE mode 5% of the time and in DEEP-SLEEP mode 95% of the time, the battery will last for nine hours.