Linear Technology DC2435A-A Demo Manual page 4

DEMO MANUAL DC2435A-A/
DC2435A-B/DC2435A-C
freQuency synchronization anD moDe selection
DC2435A's mode selector allows the converter to run in
forced continuous operation, pulse skip operation, Burst
Mode or be synchronizing to an external clock by changing
the position of JP3.
rail tracking
DC2435A is configured for an on board soft start circuit.
The soft start ramp rate can be adjusted by changing the
value of C47. DC2435A can also be modified to track an
external reference. Refer to Table 3 for tracking options
and to the data sheet for more details.
optional inDuctor Dcr current sensing
DC2435A 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
Table 4. Optional Inductor DCR Current Sensing
CONFIGURATION
Current Sense Resistor (Default)
Inductor DCR Current Sensing
low Quiescent current applications anD measurement
The typical quiescent current (I
is 29µA in sleep mode as specified in the LTC7813 data
sheet. However, the input current of the DC2435A board
can be higher than this value because of additional circuit
outside of the IC. To reduce the total input current, large
value FB divider resistors should be used. In addition, some
of the optional pull-up resistors should be removed from
4
CHANNEL 1 RS1
CHANNEL 2 RS2
Ref. Sch.
0Ω Copper
) of the LTC7813 controller
Q
Table 2. Mode Selection and Synchronized Operation Options
CONFIGURATION
Forced Continuous Operation
Pulse-Skipping Operation
Synchronized to External Clock Applied to CLKIN Pin
Burst Mode Operation
Table 3. V Tracking Options
OUT1
CONFIGURATION
Soft-Start Without
Tracking (Default)
V Tracking Scaled
OUT1
External Reference
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 4 for Optional Inductor DCR Current Sensing
setup and to the data sheet for more details.
R39 R40 C15
R80 R81 C56
Ref. Sch. Ref. Sch. Ref. Sch.
OPEN OPEN Calculated Value from Data Sheet
the board. Refer to Table 5 for the low input quiescent
current setup.
Table 5. Low Input Quiescent Current Configuration
Reference Designator
Function
Stuffing Option
R34 R37 C47
OPEN OPEN 0.1µF
Resistor Divider OPEN
R51 R53
R89 R90
OPEN OPEN
PGOOD1
OPEN
JP3
FCM
PS/Sync
PS/Sync
Burst
TRK/SS1
TURRET
OPEN
External
Reference
R62
R91
OPEN
0Ω
R46
dc2435af