IRDC3870
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IRDC3870 EVALUATION BOARD
The IR3870 SupIRBuck
TM
is an easy-to-use,
fully integrated and highly efficient DC/DC
voltage regulator. The onboard constant on
time hysteretic controller and MOSFETs
make IR3870 a space-efficient solution that
delivers up to 10A or precisely controlled
output voltage in 60°C ambient temperature
applications without airflow. It is housed in a
in 20 Lead 5mmx6mm QFN package.
Key features offered by the IR3870 include:
programmable switching frequency, soft
start, and over current protection allows for a
very flexible solution suitable for many
different applications and an ideal choice for
battery powered applications.
Additional features include pre-bias startup,
very precise 0.5V reference, over/under voltage
shut down, power good output, and enable
input with voltage monitoring capability.
This user guide contains the schematic and bill
of materials for the IRDC3870 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed specifications
and application information for IR3870 is
available in the IR3870 data sheet.
BOARD FEATURES
•
V
in
= +12V Typical ( 8-19V input Voltage range. see note below)
• PV
cc
= +5.0V
• Vcc=+3.3V
•
V
out
= +1.1V @ 0- 10A
• F
s
= 500kHz @ 10A
•
L = 0.56uH
•
C
in
= 1x10uF (ceramic 1210) + 1x68uF (electrolytic)
•
C
out
= 2x10uF (ceramic 0805) + 1x150uF(SP Cap)
Note: At low input line an additional 10uF ceramic capacitor is recommended at
input to handle higher ripple current)
1
IRDC3870
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN and PGND. A maximum 10A load should
be connected to VOUT and PGND. The connection diagram is shown in Fig. 1 and inputs and outputs of
the board are listed in Table I.
IRDC3870 has three input connectors, one for biasing (PVcc),one for biasing Vcc and the third one as input
voltage (Vin). Separate supplies should be applied to these inputs. PVcc input should be a well regulated
4.5V-5.5V supply and it would be connected to PVcc and PGND and Vcc input should be a well regulated
3.0V-3.6V supply and it would be connected to Vcc and PGND. An external signal can be provided as
Enable signal to turn on or turn off the converter. The absolute maximum voltage of Enable signal is +3.9V.
A well regulated 0-2V signal source is used in this user guide.
The evaluation board is configured for use with 2x10uF (ceramic 0805) + 1x150uF (SP) capacitors.
However, the design can be modified for an all ceramic output cap configuration by adding the inductor
DCR sensing circuit as show in the schematic on page 8.
Table I. Connections
Connection
VIN (TP53)
PGND (TP55)
PVcc+ (TP61)
Vcc+ (TP59)
PGND (TP62)
PGND (TP60)
VOUT (TB5)
PGND (TB6)
Enable (TP52)
Signal Name
VIN (+12V)
Ground of VIN
PVcc input (+5.0V)
PVcc input (+3.3V)
Ground for PVcc input
Ground for Vcc input
V
out
(+1.1V)
Ground of V
out
Enable input
LAYOUT
The PCB is a 4-layer board. All layers are 2 Oz. copper. The IR3870 and other components are
mounted on the top and bottom side of the board.
Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located
close to IR3870. The feedback resistors are connected to the output voltage at the point of regulation
and are located close to IR3870. To improve efficiency, the circuit board is designed to minimize the
length of the on-board power ground current path.
2
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