Linear Technology 868 Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 868
LOW QUIESCENT CURRENT DUAL SYNCHRONOUS BUCK CONVERTER

DESCRIPTION

Demonstration circuit 868 is a dual-output stepdown
power supply. The input voltage is from 4.5V to 32V.
The supply has two outputs: 3.3V/5A
8.5V/3.5A . When the input voltage is close to the
MAX
output voltage, the supply is in dropout mode. The de-
sign features the LTC3827-1, the low quiescent current,
2-phase, dual-output synchronous buck regulator.
Operating the two high side MOSFETs 180 degrees out
of phase significantly reduces peak input ripple current;
thereby reducing input capacitance and EMI noise. Both
controllers have internal current foldback for overload
condition. Current foldback limits MOSFET heat dissipa-
Table 1. Performance Summary
PARAMETER
Input Voltage Range
Outputs
Typical Output Ripple (V
OUT1
Typical Output Ripple (V
OUT2
Typical Operating Frequency
Typical input current@no load
Efficiency for Vout1
Efficiency for Vout2
Demonstration circuit 868 is easy to set up to evaluate
the performance of the LTC3827-1. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
Place RUN1 and RUN2 in OFF position, the FREQ
1.
jumper at the selected
PLLIN/MODE jumper JP2 in desired Mode (Burst or
CCM Mode) position. Table 2 shows the default set-
ting for DC868.
MAX
CONDITION
If the input voltage must exceed 32V, use higher voltage rating input capacitors. The IC
works up to 36V. Minimum of 9V input is needed for 8.5V output regulation at 3A load.
V = 3.3V, 0A to 5A
OUT1
V = 8.5V, 0A to 3.5A, Vin>9V
OUT2
) 20MHz BW, 5A load, V = 32V, frequency = 400kHz
IN
) 20MHz BW, 3.5A load, V
IN
PLLLPF floating (position JP1 to 400Khz)
CH1 on, no load, CH2 off, frequency=400kHz, Vin=16V, Burst Mode
VIN=12V, Vout1=3.3V at 3.5A, frequency =400KHz
VIN=12V, Vout2=8.5V at 2.5A, frequency =400kHz
frequency and
tion during short-circuit conditions. The LTC3827-1 fea-
tures a precision 0.8V reference and a power good out-
and put indicator. The PLLIN/MODE pin selects among Burst
Mode operation, pulse skipping mode, or continuous
inductor current mode at light loads. The controller can
operate at up to 99% duty cycle for very low dropout
capability.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
= 32V, frequency = 400kHz
JP1 JP2
FREQ PLL/MODE
400kHz BURST
Table 2. Default Jumper Settings
the
Connect the desired loads between 3.3V and 8.5V
2.
terminals and their closest PGND terminals on the
board.
LTC3827EG-1
VALUE
4.5V to 32V
3.3V ± 2%
8.5V ± 2%
35mV
P-P
30mV
P-P
400kHz
85uA
94%
98%
JP3 JP4 JP5
RUN1 RUN2 TRACK1
ON ON SS1
JP6
TRACK2
SS2
1