Linear Technology DC776 Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 776
DESCRIPTION
Demonstration circuit 776 is a 36V-72Vin, forward
converter featuring the LTC3705 and LTC3706. This
circuit was designed specifically to attain a high step-
down ratio power supply in one stage in order to ef-
ficiently power 1.5V loads from a typical telecom in-
put voltage range. Isolation voltage is 1500VDC.
This circuit features secondary-side control of the
Table 1. Performance Summary (T
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
OUT
Maximum Output Current
Typical Output Ripple V
OUT
Output Regulation
Dynamic Response
Nominal Switching Frequency
Efficiency
On/Off Control
Isolation Voltage
OPERATING PRINCIPLES
The LTC3706 controller is used on the secondary and
the LTC3705 driver with self-starting capability is
used on the primary. When an input voltage is ap-
plied, the LTC3705 begins a controlled soft-start of
= 25°C)
A
CONDITION
V = 36V to 72V, I
IN
400LFM
200LFM
V = 48V, I = 30A (20MHz BW)
IN OUT
Line
Load
Peak Deviation
Load Step of 20A to 40A (1A/us min)
Settling Time (to within 15mV of set point)
V = 48V, I = 45A, 400LFM
IN OUT
Logic Low Voltage-Off
Logic High Voltage-On
Basic Insulation
36V-72VIN, FORWARD CONVERTER
LTC3705 and LTC3706
supply without the need of an optocoupler, self-
starting architecture, input undervoltage lockout, and
output overvoltage protection.
Design files for this circuit board are available.
Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
= 0A to 45A, 400LFM
OUT
the output voltage. As this voltage begins to rise, the
LTC3706 secondary controller is quickly powered up
via T1, D3, and Q13. The LTC3706 then assumes
control of the output voltage by sending encoded
VALUE
36V
72V
1.5V ± 1%
45A
40A
30mV
P–P
±0.01%
±0.18%
65mV
50us
215kHz
84.75% Typical
1V MAX
2.5V MIN
1500VDC
1