Direct-through function is on! This controller with an efficiency of 99.9% is worth having~

Latest update time：2020-03-04

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A common DC-DC converter problem is to generate a regulated voltage when the input voltage may be above, below, or equal to the output, that is, the converter must perform both step-up and step-down operations. Powering automotive electronics from a nominal 12 V battery is a typical scenario, ranging from engine cold crank (as low as 3 V) to load dump (up to 100 V) or reverse battery voltage due to operator error (voltages vary quite widely).

From SEPIC to 4-switch topologies, there are several DC-DC converter topologies that can perform both step-up and step-down operations, but none of these solutions can directly pass the input voltage to the output with the switches actively activated, and this is still the case.

The LT8210 is a synchronous buck-boost controller that can operate in Pass-Thru™ mode, helping to eliminate EMI and switching losses and maximize efficiency (up to 99.9%). The pass-through feature passes the input directly to the output when the input voltage is within a user-programmable window. The LT8210 operates over an input voltage range of 2.8 V to 100 V, so it regulates from the lowest input voltage during cold crank to the peak amplitude of an unrestrained load dump. The LT8210 can operate as a traditional buck-boost controller with pin-selectable continuous conduction mode (CCM), pulse skipping, or Burst Mode® ^operation , or in Pass-Thru mode where the output voltage is regulated according to a programmed window. When the input voltage in this window is passed directly to the output without actively switching the FETs, operation is performed with very low I _Q and no switching noise.

Direct operation mode

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.

Figure 1. LT8210 8 V to 16 V pass-through regulator circuit

Figure 2 shows the input/output transfer characteristic 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 is below the pass-through window, the LT8210 steps it up and keeps the output at 8 V. When the input voltage is within the pass-through window, the top switches A and D remain on, allowing the output to track the input, and the part can enter a low power state with typical quiescent currents of 4 µA and 18 µA on the V _IN and V _INP pins, respectively. In this non-switching state, there is neither EMI nor switching losses, so efficiencies of more than 99.9% can be achieved.

Figure 2. In the pass-through input voltage window, pass-through operation efficiency can reach 99.9%.

Figure 3. In pass-through mode, the LT8210 quickly responds to an 80 V unsuppressed load dump pulse, limiting the output to a programmable 16 V maximum.

Figure 4. In pass-through mode, the LT8210 responds to a cold-crank pulse (<4 V) by boosting to a programmable 8 V minimum output voltage.

Figure 5. Efficiency in the pass-through region reaches nearly 100% (compared to efficiency in continuous conduction mode).

Figure 6. The LT8210 features ultralow quiescent current in the pass-through region.

in conclusion

Automotive batteries and similar wide voltage range power sources are complex issues for DC-DC converter designers, requiring protection and the ability to efficiently perform step-down and step-up conversions. 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. It operates between 2.8 V and 100 V and provides built-in reverse voltage protection. The 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 Mode® operation
Programmable non-switching pass-through window
18μA Pass-through Mode I Q , 99.9% Efficiency
V IN Range: 2.8V to 100V (4.5V at Startup)
VOUT range : 1V to 100V
Reverse input protection up to –40V
±1.25% Output Voltage Accuracy (–40°C to 125°C)
±3% Accurate Current Monitoring
±5% Accurate Current Regulation
10V Quad N-Channel MOSFET Gate Driver
EXTV CC LDO powers the driver from V OUT /external power rail
±20% Cycle-by-Cycle Inductor Current Limit
No top MOSFET refresh noise in buck or boost mode
Fixed/Phase-lockable frequency: 80kHz to 400kHz
Spread spectrum frequency modulation (SSFM) for low EMI
Power Good Output Voltage/Overcurrent Monitor
Available in 38-lead TSSOP and 40-lead (6mm × 6mm) QFN packages

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