DC385 Introduction
Description
Demonstration circuit DC385 is a high density synchronous step-down (buck) regulator
using the LTC1778 No RSENSE™ switching regulator controller. This controller uses a
valley current control architecture to deliver very low duty cycles without requiring a
sense resistor. It provides high efficiency operation at light loads by means of
discontinuous mode operation. Noise and RF interference are reduced by means of a
forced continuous control pin. The circuit uses a dual SyncFET™ and has a very small
footprint. With a wide operating range of VIN from 5V to 28V and a duty cycle of 2% to
90% at 200kHz, the circuit demonstrates that the LTC1778 is ideal for applications such
as notebook and palmtop computers, PDAs, battery chargers and distributed power
systems.
Quick Start Guide
This demonstration board is easily set up to evaluate the performance of the LTC1778.
Please follow the procedure outlined below for proper operation.
1. Connect input power to the VIN and GND terminals. Input voltage is limited to
between 5V to 28V. Refer to Figure 1 for proper measurement equipment setup.
2. Connect the load between the VOUT and GND terminals.
+–
+
–
+
–
+–
+–
VIN GND
GND
VOUT
SGND
IMVPII I/O POWER SUPPLY
DC385A
LTC1778EGN
LOAD
Figure 1. DC385 Test and Measurement Setup
3. Connect the FCB signal to the SGND terminal to force continuous synchronous
operation at low loads; connect the FCB signal to the INTVCC signal to enable
discontinuous mode operation at low loads (see solder pads on bottom side of
assembly).
4. To shut down the circuit, connect the RUN/SS signal to the SGND terminal.
Disconnect the RUN/SS signal from the SGND terminal to enable normal
operation.
5. When measuring input or output ripple, see Figure 2 for proper scope probe
technique.
Vout
GND
Figure 2. Scope Probe Position for Ripple Measurement
SyncFET is a trademark of International Rectifier
