QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 412
LOW INPUT VOLTAGE, HIGH CURRENT BUCK CONTROLLER
LTC3713
DESCRIPTION
Demonstration Circuit 412 is a synchronous step-down
regulator using the LTC3713 No R
SENSE
TM
switching
regulator controller. It can operate at low input voltage
down to 1.7V and supply up to 10A of output current.
Higher current can be obtained by changing external
components. DC412 provides a low input buck regulator
to supply lower voltages for microprocessors, DSPs,
and bus termination applications. An onboard boost
converter generates the gate-drive voltage for the exter-
nal power MOSFETs and allows the use of standard 5V
logic-level N-Channel MOSFETs.
Design files for this
circuit board are available. Call the LTC factory.
JP1 sets the operation mode. The lower position selects
Forced Continuous synchronous operation, which mini-
mizes noise and RF interference, and also allows the
output to sink current for applications like bus termina-
tors. RSNS1, RSNS2, R7, R8 and D1 help in modifiying
the design for symmetric current limit. Please refer to
the “Applications Requiring Symmetric Current Limit”
section in the LTC3713 data sheet for details.
Table 1.
Performance Summary
PARAMETER CONDITION VALUE
Input Voltage Range 1.7V to 6V
Maximum Output
Current
V
IN
= 1.7V to 6V 10A
Outputs* 0 to 10A 1.25V
±
3%
Typical Output Ripple 10MHz BW; 10A Load; V
IN
= 3.3V 15mV
P-P
Typical Load Regulation I
OUT
= 0A to 10A; V
IN
= 3.3V -10mV
Efficiency V
IN
= 3.3V, V
OUT
= 1.25V,
I
OUT
= 10A
83%
*Higher output current can be achieved by using higher current rating
inductor and adding parallel MOSFETs (M3, M4).
QUICK START PROCEDURE
Refer to Figure 1 for proper measurement equipment
setup and follow the procedure below:
1.
Connect the input power supply to the VIN and GND
terminals.
NOTE:
Do not increase V
IN
over 6V (If higher input
voltage is desired, use higher voltage rating input
capacitors. If the input voltage is always higher than
4V, you probably want to consider using demo circuit
DC378, which features the LTC1778.)
2.
Connect the desired load between the VOUT and GND
terminals. Soldered wires should be used to achieve
optimum performance.
3.
Shunt JP2 and JP4 for operation. V
OUT
goes to 0V
with either JP2 or JP4 open. If JP3 is connected,
overcurrent latchoff is disabled. Refer to the “Applica-
tions Information” section in the LTC3713 data sheet
for details.
4.
Set the FCB Jumper JP1 to the lower position to force
continuous synchronous operation at light loads; or
to the upper position to enable discontinuous mode
operation at light loads.
5.
When measuring the output ripple, see Figure 2 for
the proper technique using the scope probe.
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 412
LOW INPUT VOLTAGE, HIGH CURRENT BUCK CONTROLLER
+
–
+
–
+–
LOAD
+
–
+– +–
DISCONTINUOUS
OVERCURRENT
LATCHOFF
DISABLE
CONTINUOUS
ENABLE
ENABLE VIN2
Figure 1.
Proper Measurement Equipment Setup
VIN
GND
Figure 2.
Scope Probe Placement for Measuring Output Ripple
2
