4
dc2117af
DEMO MANUAL DC2117A
optional inDuctor Dcr current sensing
low Quiescent current applications anD measurement
Demonstration circuit 2117A provides an optional circuit
for inductor DCR current sensing. Inductor DCR current
sensing uses the DCR of the inductor to sense the inductor
current instead of discrete sense resistors. The advantages
of DCR sensing are lower cost, reduced board space and
higher efficiency, but the disadvantage is a less accurate
current limit. If DCR sensing is used, be sure to select an
inductor current with a sufficiently high saturation current
or use an iron powder type material.
Refer to Table 3 for optional inductor DCR current sensing
setup and to the data sheet for more details.
Table 3. Optional Inductor DCR Current Sensing
CONFIGURATION
RS1
R24
R28
C16
R37
R38
R39
R40
Current Sense
Resistor (Default)
Ref Sch
Ref Sch
Ref Sch
OPEN
OPEN
OPEN
OPEN
OPEN
Inductor DCR Current
Sensing
0Ω Copper
OPEN
OPEN
Calculated Value from Data Sheet
0Ω
0Ω
The typical quiescent current (I
Q
) of the LTC3895 controller
is 40µA in sleep mode as specified in the LTC3895 data
sheet. However, the input current of the DC2117A board
can be higher than this value because of additional circuit
Table 4. Low Input Quiescent Current Configuration
Reference Designator
R1
R2
R23
JP3
JP4
JP5
JP8
Function
OVLO
PGOOD
INTV
CC
Jumper
MODE Selector
100% DUTY
BIAS Supply
Stuffing Option
OPEN
0Ω
OPEN
OPEN
BURST ADJ or
BURST DEFAULT
OFF
OFF
outside of the IC. To reduce the total input current, large
value FB divider resistors should be used. In addition, some
jumpers and resistors should be configured accordingly.
Refer to Table 4 for the low input quiescent current setup.