Introduction and Application Analysis of LTC3622 Dual 1A Synchronous Monolithic Step-Down Regulator

The LTC3622 dual 1A synchronous monolithic buck regulator enables compact, high efficiency power supplies for battery-powered systems and portable devices as well as general point-of-load regulation. The tiny 14-pin, 3mm x 4mm DFN package accepts an input voltage of 2.7V to 17V and can produce two adjustable outputs of ±1% with a 0.6V to VIN input, while providing up to 1A on both channels Output current.

When the two channels are enabled, the LTC3622's quiescent current is as low as 5μA in Burst Mode operation and below 0.1μA in shutdown. The switching frequency is fixed at 1MHz or 2.25MHz and is connected to an external clock. It can have a ±50% synchronization range. Optional burst mode operation produces the highest efficiency, while pulse skip mode minimizes ripple to meet noise sensitive applications.

Dual 3.3V and 5V, 1A output (at 1MHz)

Figure 1 shows a dual output converter that accepts an input voltage range of 5V to 17V and produces a 1A output at 3.3V and 5V.

Figure 1: A dual 1A converter with 3.3V and 5V output, fSW = 1MHz

Both channels can operate in phase or with a 180° phase shift (selected by connecting the PHASE pin to GND or INTVCC). This gives the user the flexibility to separate the switching edges of the channel and try to suppress any noise coupling. The LTC3622 has two peak current limit levels that can be selected from the ILIM pin to 1.8A or 1A. This optional current limit allows the use of smaller inductors in lower current designs, minimizing resolution The size and cost of the solution.

Under heavy load conditions, the regulator operates in a continuous inductor current mode with small output ripple and high efficiency. Two discontinuous conduction modes (DCM) are provided under light load conditions to achieve high efficiency and minimize energy consumption. To further reduce power loss and extend battery life under very light or no-load standby conditions, burst mode operation can be selected by connecting the MODE / SYNC pin to INTVCC. In this case, the LTC3622 IC consumes only 5μA under no-load conditions. Burst mode operation may increase the output voltage ripple. On the other hand, if minimizing VOUT ripple is critical, the pulse skip mode can be selected by grounding the MODE / SYNC pin. This mode produces lower ripple than burst mode operation, but at the cost of a slight decrease in efficiency. In addition, connecting the MODE / SYNC pin to an external clock synchronizes the switch clock to the external clock and places the device in pulse skip mode. Figure 2 shows the conversion efficiency from 12 VIN to 5 VOUT in burst mode and pulse skip mode.

Figure 2: Efficiency of the 5V output of the dual supply shown in Figure 1, VIN = 12V, VOUT2 = 5V, fSW = 1MHz

The LTC3622 is a reliable current mode regulator with fast, cycle-by-cycle overcurrent protection and excellent voltage and load transient response. As the input voltage decreases, the duty cycle increases and slope compensation is required to maintain a stable current feedback loop. The LTC3622 has an internal circuit for accurately maintaining a constant peak current limit and a stable loop, even under high duty cycle conditions.

In applications such as battery-powered systems, the input voltage will have a very wide range. When VIN falls close to VOUT and the converter duty cycle approaches 100%, the LTC3622 enters the differential operation state to maintain VOUT regulation. In the differential pressure state, the device will switch to sleep mode and exit from sleep mode based on the output load current. This significantly reduces the quiescent current while maintaining regulation of VOUT, which extends the runtime of the input battery supply. As shown in Figure 3, the LTC3622 is capable of achieving high efficiency in the range of microamps to full load with a differential pressure condition.

Figure 3: Efficiency vs. Load Current in Differential Pressure State, VIN = 5V, VOUT2 = 5V, fSW = 1MHz

To simplify design and minimize component count, the LTC3622 features internal loop compensation. If desired, a feedforward capacitor in parallel with the upper feedback resistor can be added to further increase the phase margin. Thanks to its current mode control, the LTC3622 power supply is stable with a variety of output capacitors. In the dual supply shown in Figure 1, each channel output requires only a small 1206 package size, 47μF ceramic capacitor. Figure 4 shows the transient response of the 5V output. For a 10% to 100% load step, the peak-to-peak voltage offset is approximately ±330mV. Additional capacitors can be added to further reduce VOUT transients. In this case, the LTpowerCAD design tool and the LTspice simulation tool can be used to optimize the design with the built-in LTC3622 model.

Figure 4: Transient response of the 5V supply shown in Figure 1, VIN = 12V, VOUT2 = 5V, IOUT2 ​​= 100mA – 1A, burst mode operation

in conclusion

The LTC3622 is a dual 1A, high efficiency synchronous monolithic step-down regulator with ultra-low quiescent current. It addresses converter efficiency and space constraints caused by battery-powered systems, point-of-load power supplies, and portable devices.

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