QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 868
LOW QUIESCENT CURRENT DUAL SYNCHRONOUS BUCK CONVERTER
1
LTC3827EG-1
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
MAX
and
8.5V/3.5A
MAX
. When the input voltage is close to the
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-
tion during short-circuit conditions. The LTC3827-1 fea-
tures a precision 0.8V reference and a power good out-
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.
Table 1.
Performance Summary
PARAMETER
CONDITION
VALUE
Input Voltage Range
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.
4.5V to 32V
Outputs
V
OUT1
= 3.3V, 0A to 5A
3.3V
±
2%
V
OUT2
= 8.5V, 0A to 3.5A, Vin>9V
8.5V
±
2%
Typical Output Ripple (V
OUT1
)
20MHz BW, 5A load, V
IN
= 32V, frequency = 400kHz
35mV
P-P
Typical Output Ripple (V
OUT2
)
20MHz BW, 3.5A load, V
IN
= 32V, frequency = 400kHz
30mV
P-P
Typical Operating Frequency
PLLLPF floating (position JP1 to 400Khz)
400kHz
Typical input current@no load
CH1 on, no load, CH2 off, frequency=400kHz, Vin=16V, Burst Mode
85uA
Efficiency for Vout1
Efficiency for Vout2
VIN=12V, Vout1=3.3V at 3.5A, frequency =400KHz
VIN=12V, Vout2=8.5V at 2.5A, frequency =400kHz
94%
98%
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:
1.
Place RUN1 and RUN2 in OFF position, the FREQ
jumper at the selected frequency and the
PLLIN/MODE jumper JP2 in desired Mode (Burst or
CCM Mode) position. Table 2 shows the default set-
ting for DC868.
JP1
FREQ
JP2
PLL/MODE
JP3
RUN1
JP4
RUN2
JP5
TRACK1
JP6
TRACK2
400kHz
BURST
ON
ON
SS1
SS2
Table 2. Default Jumper Settings
2.
Connect the desired loads between 3.3V and 8.5V
terminals and their closest PGND terminals on the
board.