Summary of Linear applies switched-capacitor step-down topology for inductor-less DC/DC
Summary: The LTC7820 is a high-power fixed-ratio charge-pump DC/DC controller that replaces inductors with switched-capacitor energy storage, enabling non-isolated intermediate-bus converters with up to 50% smaller circuit size and up to 4000 W/in³ power density. It operates from 6V to 72V (80V abs max), can deliver hundreds of watts (example: 500W at 72V), achieves efficiencies up to 99%, supports 2:1, 1:2 and 1:1 ratios (and cascaded 4:1), and can implement higher ratios like 6:1 using Dickson topology.
Parts used in the LTC7820 project:
- LTC7820 charge-pump DC/DC controller IC
- External MOSFETs (FETs) for switching
- Capacitors for switched-capacitor energy storage
- PCB and connectors for non-isolated intermediate bus converter
- Optional second LTC7820 IC for cascading (4:1 step-down)
LTC7820 is, a high power fixed ratio charge pump DC/DC controller that eliminates the power inductor in a non-isolated intermediate bus converter, allowing up to a 50% reduction in circuit size and up to 4000 W/in³ power density. The 72V fixed-ratio DC/DC controller can deliver 500W.
Non-isolated regulators and voltage level converters that employ energy storage in capacitors rather than inductors are well-known, but the majority of DC/DC designs in recent times have used magnetics. Indeed, a feature of various companies’ presentation of devices that use ever-higher switching speeds is the ability to reduce the size of the inductor. Now, Linear Technology (now part of Analog Devices) has eliminated the inductor and introduced the LTC7820, that employs energy storage on capacitors and that drives external MOSFETs in voltage divider, doubler or inverter configurations with an efficiency of up to 99%. As the energy storage is not in an inductance, there cannot be a transformer so the topologies available – which include the ‘Dickson converter’ – are necessarily non-isolated. The IC’s open loop fixed duty is suitable for non-isolated intermediate bus applications in power distribution, datacom, telecom, high-end computing and industrial systems.
The LTC7820 charge-pump controller operates over a 6V to 72V (80V abs max) input voltage range and can produce output currents in multiple-tens of Amps, depending on the topology and choice of external components (FETs/capacitors). It can be configured for a 2:1 step-down ratio from an input voltage up to 72V. Two of the LTC7820 ICs can be cascaded for a 4:1 step-down ratio. For even higher step-down ratios, such as a 6:1, the Dickson converter topology is recommended and is suitable for 54V input to a 9V outputs, requiring only a single LTC7820. The LTC7820 can also be configured for a 1:2 step-up ratio or a 1:1 inverter ratio from an input voltage as high as 36V.
Read more: Linear applies switched-capacitor step-down topology for inductor-less DC/DC
- What is the input voltage range of the LTC7820?
It operates over a 6V to 72V input voltage range with 80V absolute maximum. - Can the LTC7820 deliver high output power?
Yes; it can produce output currents in multiple-tens of Amps and can deliver up to 500W in examples given. - Does the LTC7820 use an inductor for energy storage?
No; it uses switched-capacitor energy storage instead of inductors. - What conversion ratios can the LTC7820 implement?
It can be configured for 2:1 step-down, 1:2 step-up, and 1:1 inverter ratios; two ICs can be cascaded for 4:1 step-down. - How can higher step-down ratios like 6:1 be achieved?
Higher ratios such as 6:1 are recommended using the Dickson converter topology with a single LTC7820. - Is the LTC7820 suitable for isolated converter designs?
No; because energy storage is on capacitors there is no transformer, so topologies are necessarily non-isolated. - What efficiency can the LTC7820 reach?
The LTC7820 can achieve efficiencies of up to 99%. - Where is the LTC7820 intended to be used?
It is suitable for non-isolated intermediate bus applications in power distribution, datacom, telecom, high-end computing and industrial systems.
