FEATURES
 | Optimized IC & MOSFETs for best electrical and thermal performance |
| DC Bus primary side controllers |
| +/- 1A gate drive current |
| Optimized for IR’s low charge MOSFETs |
| Adjustable dead-time (50nsec to 200nsec) |
| High & low pulse-width matching to within +/-25nsec |
| Programmable switching frequency up to 500kHz |
| Integrated soft-start |
| Vcc supply under-voltage lock-out |
| Current limit |
 | IR2085S |
| - Self-oscillating, 50% duty cycle design with 100V offset half-bridge driver in a single 8 pin SOIC package |
| IR2086S |
| - Self-oscillating, 50% duty cycle design with 100V offset full-bridge driver in a single 16 pin SOIC package |
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HALF-BRIDGE DC BUS CONVERTER SCHEMATIC
FULL-BRIDGE DC BUS CONVERTER SCHEMATIC
The DC Bus chip sets are designed for the isolated front-end of two-stage distributed power
architectures (DPA) with an intermediate bus voltage feeding non-isolated point-of-load
(POL) converters. Two-stage DPA schemes do not require a tightly regulated intermediate
bus voltage, since the POL will typically accept a relatively wide input voltage,
and the POL provides the needed regulation to the load. In addition, multiple DC Bus
Converter Chip Sets can be placed in parallel for higher power requirements.
The chip sets consist of either a primary side half-bridge or full-bridge controller combined with
optimized primary side & secondary side DirectFET MOSFETs see selector table below. In addition, the
IRF7380 can be used for deriving primary side bias, and the IRF6621 can be used for the secondary
side gate clamp. SO-8 packaged MOSFETs can be used on the primary side and secondary side for lower power
applications.
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The half-bridge IR2085S and full-bridge IR2086S control ICs are at the heart of the DC Bus converter
architecture, based around a 50% fixed duty cycle, self-oscillating control scheme. The IR2085S replaces
two SO-8 packaged devices, and the IR2086S replaces three, and are optimized for DPA applications. Features
include an integrated soft-start capacitor that gradually increases duty cycle from zero to 50% over 2000
cycles to limit in-rush current during start-up, and maintains equal pulse-widths for the high- and low-side
MOSFETs throughout the start-up sequence.
The low-side and high-side pulses for the half- and full-bridge are matched to within ±25nsec to prevent
transformer imbalances during operation. Other features include ±1A gate drive current optimized to work
with IR’s next generation low charge primary side MOSFETs, and includes adjustable dead-time from 50nsec
to 200nsec to protect against shoot-through current. The deadtime can also be adjusted to limit the amount
of body diode conduction on the secondary side, therefore maximizing efficiency.
The IR2085S and IR2086S both have programmable switching frequency up to 500kHz for design flexibility.
Higher switching frequency decreases output voltage ripple and allows use of smaller, lower loss magnetic
components. Circuit designers can control switching frequency and deadtime independently with just two
external components to customize circuits for their particular application.
A floating channel designed for bootstrap operation up to +100V DC and VCC supply under-voltage lockout
is included. The IR2085S and IR2086S both use a new high voltage, high frequency level shift technology with high dv/dt
immunity. The immunity is in the range of 50V/nsec to prevent unwanted turn-on of the lower MOSFET in the
half- or full-bridge, and enables faster switching speed.
On the primary side, either 80V or 100V MOSFETs can be selected depending on required voltage derating in
the application. IR’s new 80V & 100V DirectFET MOSFETs provide optimized performance for both the half- and
full-bridge topologies bringing benchmark on-state resistance and gate charge specifications as well
as allowing improved thermal performance versus competing solutions.
On the secondary side, either 30V or 40V MOSFETs can be selected depending on required voltage
derating in the application. IR’s new 30V & 40V DirectFETs provide optimized performance in the
self-driven synchronous rectification topology bringing benchmark on-state resistance as the
primary key figure of merit as well as allowing improved thermal performance versus competing
solutions.
IR’s new architecture uses two biasing components. The IRF9956 or IRF6621 can be used to provide
a gate clamp for the secondary side synchronous rectification MOSFETs, clamping the drive voltage
to 7.5V.
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Single isolated 48V Bus Converter to generate unregulated low output voltage in 8V range, ideal for powering Point of Load (POL) Converters
Click here for more efficiency curves.
Thermal Image at 35A, 48VIN, 330W, 400LFM
Optimised IC and MOSFETs for best electrical and thermal performance
The DC Bus Converter Chip Set simplifies and improves on-board power management for networking and communications systems.
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