DC/DC converter, both step-up and step-down must be performed
ADI LT8210 controller operating in pass-through mode
Eliminates EMI and switching losses, with efficiency up to 99.9%


A DC/DC converter must generally produce a regulated voltage when the input voltage is higher, lower, or equal to the output. That is, the converter must perform both step-up and step-down functions.

These situations are common when powering automotive electronics from a nominal 12V battery, and can range from engine cold crank which can drop to as low as 3V, to load dumps that can reach 100V, or even reverse battery voltage due to operator error.

There are several DC/DC converter topologies that can perform both step-up and step-down operations, from SEPIC to 4-switch topologies, but none of these solutions to date can directly transfer the input to the output without active switching.

The LT8210 is a synchronous buck-boost controller that can operate in Pass-Thru™ mode, eliminating EMI and switching losses while maximizing efficiency up to 99.9%. Pass-through operation passes the input directly to the output when the input voltage is within a user-programmable range.

The LT8210 operates over an input voltage range of 2.8V to 100V, allowing it to regulate from minimum input voltage during cold crank to the peak amplitude of an unsuppressed load dump.

It can operate as a conventional buck-boost controller in pin-selectable continuous conduction mode (CCM), pulse-skipping, or Burst Mode® operation, or in a novel pass-through mode where the output voltage is regulated over a programmed range.

When the input voltage is in this range, the input voltage is directly transferred to the output without actively switching the FET, enabling low I _Q operation and no switching noise.


Pass-through operation mode

Figure 1 is a simplified schematic of the LT8210 configured for pass-through operation with the output regulated between 8 V and 16 V. The highest and lowest voltages in the pass-through range are set by the FB2 and FB1 resistor dividers, respectively.

Figure 2 shows the input/output transfer characteristics of this circuit. When the input voltage is above the pass-through range, the LT8210 steps the input voltage down to a regulated 16V output.

If the input voltage falls below this range, the LT8210 boosts to maintain the output at 8V.

When the input voltage is within the pass-through range, the top switches A and D turn on sequentially, causing the output to track the input and the part to enter a low power state.

Typical quiescent currents at the V _IN and V _INP pins in low power states are 4 µA and 18 µA, respectively.

In this state of no switching, there is no EMI or switching loss, so efficiency of over 99.9% can be achieved.

Automotive batteries and similar wide-voltage power sources present a complex problem for DC-DC converter designers, requiring high-efficiency buck and boost conversion along with protection features.

The LT8210 synchronous buck-boost controller eliminates complexity by combining protection features with a wide input range buck-boost converter and a unique pass-through option.

The LT8210 operates over a 2.8V to 100V operating range and includes reverse voltage protection. The device's pass-through mode achieves very low quiescent current while eliminating switching losses and noise.

In pass-through mode, the output voltage is not regulated in the traditional sense, but is instead regulated over a programmable voltage range.



This article is a summary of the article titled “4 Switch Buck-Boost Controller with Pass-Thru Capability Eliminates Switching Noise” by David Megaw, Senior Design Engineer, and Bruce Haug, Product Marketing Engineer, Analog Devices.