A µModule Buck Regulator as Thin as a Coin

Latest update time：2020-10-19

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The LTM4691 is a high efficiency, dual output step-down µModule ^® buck regulator capable of delivering 2 A of continuous output current per channel from a 2.25 V to 3.6 V input voltage. This switch mode power supply is available in a small 3 mm × 4 mm × 1.18 mm LGA package. The switching controller, power FETs, inductor, and all supporting components are included in this small package. Each output can be independently set by a resistor with a programmable voltage range of 0.5 V to 2.5 V.

Figure 1. The LTM4691 is placed next to a coin and a 1210-size ceramic capacitor, showing its slim profile.

The LTM4691 can deliver 2 A per output with only a few small capacitors and resistors. The µModule regulator includes internal feedback loop compensation, which reduces the number and size of additional components. The switching frequency defaults to 2 MHz without any external components or inputs, but 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 are needed to complete the internally compensated loop - resulting in ample stability margin and excellent transient response performance. Other features include a PGOOD signal, output overvoltage protection, overtemperature protection, precision operating thresholds, and output short-circuit protection.

Small solution using all-ceramic capacitors

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

Figure 2. The small LTM4691 on the DC2910A demo board. In addition to the two input capacitors shown, the back of the board also holds output voltage setting resistors and several capacitors.

Figure 3. Simplified schematic of the LTM4691 setup with _V = 3.3 V, V = _1.2 V, V ₌ 1.8 V, and f _{=
2 MHz.}

Figure 4. LTM4691 V _IN = 3.3 V, V _OUT1 = 1.2 V, V _OUT2 = 1.8 V, f _SW = 2 MHz, I _OUT1 = 2 A, I _OUT2 = 2 A, and Ta = 23°C, no forced airflow.

Figure 5. LTM4691 efficiency curves for V _IN = 3.3 V, V _OUT1 = 1.2 V, V _OUT2 = 1.8 V, and f _{SW
= 2 MHz.}

Figure 6. Load step with V _IN = 3.3 V, V _OUT = 1.2 V, and f _{SW
= 2 MHz.}

Figure 7. Load step with V _IN = 3.3 V, V _OUT = 1.8 V, and f _{SW
= 2 MHz.}

in conclusion

Arguably just as important for compact designs, the LTM4691’s small size and compact size fit into tight spaces. The LTM4691’s high thermal performance and efficiency minimize the need for bulky thermal mitigation components. Likewise, transient response performance and output stability have not been sacrificed to fit into a tiny package.

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