3.6 V Input, Dual Output µModule Buck Regulator Produces 2 A per Channel in a 3 mm × 4 mm Footprint

Brian Lin, Applications Engineer, Analog Devices



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Figure 1. The small profile of the LTM4691 can be seen when placed next to a thin coin and a 1210-sized ceramic capacitor

­The LTM4691 is a high efficiency, dual output step-down µModule buck regulator capable of 2A continuous output current for each channel from input voltages between 2.25 V and 3.6 V. This switch-mode power supply comes in a tiny 3 mm × 4 mm × 1.18 mm LGA package. This small footprint comprises the switching controller, power FETs, inductors, and all supporting components. Each output is independently resistor programmable from 0.5 V to 2.5 V.

The LTM4691 can deliver 2A per output with just a few small capacitors and resistors. The µModule regulator includes internal feedback loop compensation, reducing the number and size of additional components. The switching frequency defaults to 2 MHz without any external component or input, but it can be synchronized to a 1 MHz to 3 MHz external clock. To maximize the performance of the feedback loop, only a few small external capacitors need be added to complete the internally compensated loop — yielding sufficient stability margins and good transient performance. Other features include a PGOOD signal, output overvoltage protection, overtemperature protection, precision run thresholds, and output short-circuit protection.

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Figure 2. The small LTM4691 on the DC2910A demo board. Other than the two input capacitors shown, output voltage setting resistors and a couple capacitors populate the back of the board


Small Solution Using All-Ceramic Capacitors

Figure 3 shows the scheme for a compact, all-ceramic capacitor solution, which takes maximum advantage of the internal circuitry of the LTM4691. Figure 2 shows a photo of the tiny solution. Figure 4, Figure 5, Figure 6, and Figure 7 show the thermal performance, efficiency, and load step performance for a DC2910A demo board.

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Figure 3. A simplified schematic for the LTM4691 setup for VIN = 3.3 V, VOUT1 =1.2 V, VOUT2=1.8V, and fSW = 2MHz


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Figure 4. LTM4691 VIN=3.3V, VOUT1 = 1.2 V, VOUT2 =1.8V, fSW = 2MHz, IOUT1 = 2A, IOUT2 = 2A, and Ta=23°C, with no forced airflow


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Figure 5. LTM4691 VIN = 3.3 V, VOUT1 = 1.2 V, VOUT2 = 1.8 V, and fSW = 2 MHz efficiency curves


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Figure 6. Loadstep at VIN =3.3 V, VOUT=1.2V, and fSW = 2MHz


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Figure 7. Loadstep at VIN=3.3V, VOUT=1.8V, and fSW = 2MHz



The LTM4691’s compact footprint and low profile enable it to fit tight spaces. Arguably just as important for compact designs: the LTM4691’s thermal performance and efficiency are high, minimizing the need for bulky thermal mitigation components. Likewise, transient performance and output stability are not sacrificed to fit the tiny package.

Analog Devices