Pass-through mode is on! Efficiency increased to 99.9%!

A common DC-DC converter problem is generating a regulated voltage when the input voltage may be higher, lower or equal to the output, that is, the converter must perform step-up and step-down operations. Powering automotive electronics from a nominal 12 V battery is a typical scenario, from an engine cold start (as low as 3 V) to a load dump (up to 100 V), or reverse battery voltage (voltage variation due to operator error) fairly broad).

A common DC-DC converter problem is generating a regulated voltage when the input voltage may be higher, lower or equal to the output, that is, the converter must perform step-up and step-down operations. Powering automotive electronics from a nominal 12 V battery is a typical scenario, from an engine cold start (as low as 3 V) to a load dump (up to 100 V), or reverse battery voltage (voltage variation due to operator error) fairly broad).

From SEPIC to 4-switch topologies, there are several DC-DC converter topologies that can perform step-up and step-down operations, but none of these solutions can directly input the input voltage to the output with active switch activation, It is still so.

The LT8210 is a synchronous buck-boost controller that can operate in Pass-Thru™ mode to help eliminate EMI and switching losses and maximize efficiency (up to 99.9%). The pass-through function passes the input directly to the output when the input voltage is within a user-programmable window. The LT8210’s input voltage range is between 2.8 V and 100 V, so it is regulated from the lowest input voltage during cold cranking, all the way to the peak amplitude of uninhibited load dump. The LT8210 can operate as a conventional buck-boost controller, supporting pin-selectable Continuous Conduction Mode (CCM), Pulse Skipping or Burst Mode® operation, or in pass-through mode, the output voltage can be adjusted according to the programming window. When the input voltage in this window is delivered directly to the output without actively switching the FET, the runtime IQ Very low and no switching noise.

pass-through mode of operation

Figure 1 shows a simplified schematic of the LT8210 configured for pass-through operation with an output regulation range of 8 V to 16 V. The top and bottom voltages of the pass-through window are set by the FB2 and FB1 resistor dividers, respectively.

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 1. LT8210 8 V to 16 V pass-through regulator circuit

Figure 2 shows the input/output transfer characteristics of this circuit. When the input voltage is above the pass-through window, the LT8210 steps it down to a regulated 16 V output. If the input voltage falls below the pass-through window, the LT8210 increases this voltage and keeps the output at 8 V. When the input voltage is within the pass-through window, top switches A and D remain on, allowing the output to track the input and the part to enter a low power state, VIN and VINP Typical quiescent currents on the pins are 4 µA and 18 µA, respectively. In this non-switching state, there is neither EMI nor switching losses, so the efficiency can reach over 99.9%.

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 2. In the pass-through input voltage window, pass-through operation efficiency can reach 99.9%

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 3. In pass-through mode, the LT8210 responds quickly to an 80 V uninhibited load dump pulse, limiting the output to a programmable 16 V maximum.

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 4. In pass-through mode, the LT8210 responds to a cold crank pulse by boosting to a programmable minimum output voltage of 8 V (

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 5. The efficiency of the pass-through region reaches nearly 100% (compared to the efficiency in continuous conduction mode).

Pass-through mode is on! Efficiency increased to 99.9%!
Figure 6. The LT8210 has ultra-low quiescent current in the shoot-through region.

in conclusion

Automotive batteries and similar wide-voltage range power supplies are complex issues for DC-DC converter designers, requiring protection and efficient buck and boost conversion. The LT8210 synchronous buck-boost controller combines protection features with a wide input range buck-boost converter and a unique pass-through option to eliminate this complexity. Its operating voltage range is between 2.8 V and 100 V with built-in reverse voltage protection. Pass-through mode helps eliminate switching losses and noise while achieving ultra-low quiescent current. In pass-through mode, the output voltage is not regulated in the traditional way, but is limited by a programmable voltage window.

LT8210

・Pin selectable pass-through or fixed output CCM, DCM, Burst Operating Mode®
・ Programmable non-switching pass-through window
・18μA pass-through mode IQ with 99.9% efficiency
・VIN range: 2.8V to 100V (4.5V at startup)
・VOUT range: 1V to 100V
・ Reverse input protection up to C40V
・ ±1.25% output voltage accuracy (C40°C to 125°C)
・ ±3% accurate current monitoring
・ ±5% accurate current regulation
・ 10V Quad N-Channel MOSFET Gate Driver
・ EXTVCC LDO powers driver from VOUT/external rail
・ ±20% cycle-by-cycle Inductor current limit
・No top MOSFET refresh noise in buck or boost mode
・Fixed/lockable frequency: 80kHz to 400kHz
・ Spread Spectrum (SSFM) for low EMI
・ Power Good Output Voltage/Overcurrent Monitor
・Available in 38-pin TSSOP and 40-pin (6mm × 6mm) QFN packages

The Links:   LM201W01-SLA1 LM150X04-A3

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