Small Footprint, High Efficiency Current-Mode Buck Regulator for Portable Electronics


Two important considerations for the power supplies used in portable electronic products are small overall size and high efficiency for longer battery life. The LTC1779, a constant frequency, current-mode step-down DC/DC converter is designed to provide both.

The LTC1779 is offered in a tiny SOT-23 package. External component count is kept to a minimum as both the high-side 250mA PMOS switching element and the current sense resistor are included on the IC. A high constant operating frequency of 550kHz (typical) allows for the use of a small external inductor.

The LTC1779 consumes only 135µA of quiescent current in normal operation and a mere 8µA in shutdown. The device features Burst Mode operation, which reduces switching losses at light load currents, thereby improving efficiency. To further extend battery life, the internal P-channel MOSFET is turned on continuously in dropout (100% duty cycle).

The LTC1779 boasts a ±2.5% output voltage accuracy. The wide input voltage range of 2.4V to 9.8V is suited for single or dual Li-Ion and 9V alkaline applications.

Single Lithium-Ion to 1.8V/250mA Step-Down Converter

Figure 1 shows the LTC1779 in a 1.8V/250mA application powered from a single Li-Ion battery input. Figure 2 shows an oscilloscope photograph of the pin 6 switching node (SW) with VIN = 3.6V and IOUT = 100mA. The switch duty cycle is equal to (VOUT + VD)/(VIN + VD), where VD is the forward voltage drop of the external diode D1 and is approximately 53%. Figure 3 is a plot of efficiency vs load current over the useful life of a single Li-Ion battery (4.2V down to 2.7V). The measured peak efficiency is 87% with VIN = 4.2V and 91% with VIN = 2.7V. For an ideal linear regulator, the corresponding efficiencies would be only 43% and 67%, respectively.

Figure 1. LTC1779 minimum component count, single Li-Ion to 1.8V/250mA step-down converter.

Figure 2. Pin 6 switching node waveform for Figure 1’s circuit.

Figure 3. Efficiency vs load current for Figure 1’s circuit.


A wide input range of 2.4V to 9.8V, low quiescent and shutdown current, high efficiency, low external parts count and small package size make the LTC1779 ideal for portable applications.


Mark Vitunic

Mark Vitunic

Mark Vitunic是ADI公司Power by Linear™部门的设计经理。他于2017年正式加入ADI公司(随ADI收购凌力尔特公司加入),之前他已在凌力尔特公司工作了19年。Mark负责管理美国马萨诸塞州北切姆斯福德和德国慕尼黑的众多项目开发工作,专注于无线功率传输、超低功耗IC、能量收集、主动电池平衡和多通道DC-DC稳压器开发。Mark拥有卡内基梅隆大学电气工程学士学位和加州大学伯克利分校电气工程硕士学位。