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dc1798af
DEMO MANUAL DC1798A
DESCRIPTION
LTC3869IGN-2
Dual, 2-Phase Synchronous
Step-Down DC/DC Controllers
Demonstration circuit 1798A is a Dual Output, Dual
Phase 5A Synchronous Buck Converter featuring the
LTC3869IGN-2. The entire circuit, including the bulk output
capacitors, fit within a 1.04" × 0.94" area on all layers. The
package style for the LTC3869IGN-2 is a 28-lead narrow
plastic SSOP.
The main features of the board include rail tracking, an
internal 5V linear regulator for bias, RUN pins for each
output, a PGOOD signal and a mode selector that allows
the converter to run in CCM, pulse-skipping or Burst
Mode operation. Synchronization to an external clock is
also possible through some minor component changes.
Two versions of the board are available.
PERFORMANCE SUMMARY
DC1798A-A has an on-board sense resistor for current
feedback, while the DC1798A-B is configured with a DCR
sense circuit that allows the converter to use the inductors
DCR as the sense element instead of the on-board sense
resistors to save cost and board space and improves
efficiency.
The input voltage range is 4.5V to 26V. The LTC3869 data-
sheet gives a complete description of the part, operation
and application information. The datasheet must be read
in conjunction with this demo manual for DC1798A.
Design files for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
PARAMETER CONDITIONS VALUE
Minimum Input Voltage 4.5V
Maximum Input Voltage 26V
Output Voltage V
OUT1
V
IN
= 6.5V to 26V, I
OUT1
= 0A to 5A 3.3V±2%
Output Voltage V
OUT2
V
IN
= 6.5V to 26V, I
OUT2
= 0A to 5A 2.5V±2%
Typical Output Ripple V
OUT
V
IN
= 26V, I
OUT1
= 5A (20MHz BW) <30mV
P-P
*
V
IN
= 26V, I
OUT2
= 5A (20MHz BW) <30mV
P-P
*
Nominal Switching Frequency 400kHz
Efficiency
See Figures 3 and 4 for efficiency
curves
DC1798A-A DC1798A-B
V
OUT1
= 3.3V, I
OUT1
= 5A; V
IN
= 16V 90%** Typical 91.0%** Typical
V
OUT2
= 2.5V, I
OUT2
= 5A; V
IN
= 16V 87.5%* Typical 88.8%* Typical
*Measured at bulk output capacitor
**Optional Mosfet (Si4816BDY) will result in up to 0.4% improvement in efficiency at full load
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of Linear Technology Corporation. All other trademarks are the property of their respective
owners.