Analog Devices 2787A Manual

DESCRIPTION
Demonstration circuit 2787A is a high efficiency, 4 phase,
hybrid converter. It can deliver 12V/100A with the input
voltage from 40V to 60V. The demo board features the
LTC 7821, which uses an architecture that merges a soft-
®
switching switched-capacitor topology with a traditional
step-down converter to provide superior efficiency com-
pared to the traditional switching architectures. It offers
a high efficiency/high density and cost effective solution
for nonisolated intermediate bus applications in power
distribution, datacom and telecom as well as emerging
48V automotive systems.
External MOSFETs switch at a 400kHz fixed frequency for
this demo board and can be programmed from 200kHz to
1.5MHz. The LTC7821's powerful 1Ω N-channel MOSFET
gate drivers maximize efficiency and can drive multiple
MOSFETs in parallel for higher power applications. Due to
its current mode control architecture, multiple LTC7821
devices can be operated in a parallel, multiphase con-
figuration with excellent current sharing and low output
PERFORMANCE SUMMARY
PARAMETER
Input Voltage Range
Output Voltage, V
OUT
Maximum Output Current, I
OUT
Typical Efficiency
Peak Efficiency
Switching Frequency
High Efficiency, Polyphase Hybrid
Specifications are at T
CONDITIONS
V = 40-60V, I = 0A to 100A
IN OUT
V = 40-60V, V = 12V
IN OUT
V = 48V, V = 12V, I = 100A
IN OUT OUT
V = 48V, V = 12V
IN OUT
DEMO MANUAL DC2787A
Step Down Converter
voltage ripple to enable much higher power applications.
Other benefits include low EMI emissions due to a soft-
switched front end and reduced MOSFET stress.
The LTC7821 design eliminates the inrush current typically
associated with switched capacitor circuits by prebalancing
the capacitors on start-up. The LTC7821 also monitors sys-
tem voltage, current and temperature for faults, and uses a
sense resistor for overcurrent protection. It stops switch-
ing and pulls the FAULT pin low when a fault condition
occurs. An onboard timer can be set for appropriate restart/
retry times. Additional features include ±1% output voltage
accuracy over temperature, a clock output for multiphase
operation, a power good output signal, short-circuit protec-
tion, monotonic output voltage start-up, optional external
reference, undervoltage lockout and internal charge bal-
ance circuitry. The LTC7821 data sheet must be used in
conjunction with this demo board manual.
Design files for this circuit board are
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= 25°C
A
LTC7821
available.
MIN TYP MAX UNITS
40 60
12
100
97.6
98
400
V
V
A
%
%
kHz
Rev. 0
1