DC786A Linear Technology, DC786A Datasheet - Page 2

• Manufacturer Part Number: DC786A
• Description: LTC4260CGN 200W Positive 48V Hot Swap Controller With Current And Voltage Monitoring (req DC590)
• Manufacturer: Linear Technology
• Series: -r

Specifications of DC786A

• Main Purpose: Power Management, Hot Swap Controller
• Embedded: No
• Utilized Ic / Part: LTC4260
• Primary Attributes: 200W, 36 ~ 72 V
• Secondary Attributes: I²C Interface
• Kit Application Type: Power Management
• Application Sub Type: Hot-Swap Controller
• Kit Contents: Quick Eval Software
• Lead Free Status / Rohs Status: Not applicable / Not applicable

The board is designed with two ground planes, on lay-
ers 2 and 3. Layer 2 is a small signal ground plane
which picks up ground for dividers, PROBE GND, the
small GND turrets, C3 and the timing capacitor, CT, as
well as all I2C and configuration jumper related
grounding.
grounding, including CIN, COUT, 3 large GND turrets,
input and output LEDs, and the input clamp and snub-
ber. These two ground planes join at PROBE GND. The
large GND turrets are provided to accommodate multi-
ple ground connections of meters, power supplies,
loads, etc., and there is no need for load current to be
routed through the circuit board.
A clear line of demarcation separates +48V copper
from ground, passing under R9, CIN, Z1, CSNUB, R27,
R1, U1, R7, C1 COUT, and R10. 55-60 mils spacing on
unpassivated surfaces is generally recommended for
48V circuits. This rule is bent in the vicinity of the
LTC4260CGN's pins 2, 3 and 4, where the spacing
necks down to about 30 mils. In practice this area
could be passivated with conformal coating, or one of
the other package options could be used (see the
LTC4260 data sheet).
CIRCUIT NOTES
DC786A uses an 8mΩ, 5% sense resistor (R5). Cou-
pled with the LTC4260's minimum current limit sense
voltage threshold of 40mV, this guarantees a minimum
current of 4.76A before the onset of current limiting or
circuit breaker action. Thus 200W is available down to
approximately 42V, dropping to ≅170W at 36V. Using a
less common sense resistor value of 7mΩ increases
the power at 36V to 195W.
The UV and OV trip points are set by separate dividers
to facilitate modification. The trip points are as follows:
UV turning on = 43V
UV turning off = 38.5V
OV turning off = 71V
OV turning on = 69.2V
A/D CONVERTER INPUT OPTIONS
2
Layer 3 is reserved for large signal
The A/D external monitor input (pin 13, ADIN) is con-
nected to a jumper, JP8, ADIN SELECT. As shipped this
jumper connects ADIN to a divider (R11, R12) which
in turn connects to the +48V input, and gives a full
scale of approximately 100V. Moving the jumper to
EXT connects R14 and R17. The board is stuffed with
R14=10kΩ and R17 is omitted; in this condition the
ADIN turret connected to the LTC4260's ADIN pin
through 10kΩ and as shown, gives a 2.56V full scale
sensitivity. R11, R12, R14, and R17 may be changed
to accommodate different scaling factors. The ADIN
pin full scale is 2.56V, ±2%.
The R11-R12 divider is built with 1% resistors, which
add up to 2% measurement error. Up to 4% total
measurement error is possible, or 2V error out of a
50V input.
MORE CURRENT
Space is provided for up to three 2010 surface mount
sense resistors, and a TO-247 (TO-3P) MOSFET. This
allows modification of the board for higher current ap-
plications. There is more copper between +48V INPUT
and +48V/5A OUTPUT than the turrets and a TO-247
can handle. The limitation is at the source of Q1, where
the trace narrows to about 200 mils X 4 layers, all 1
ounce. This is good for about 40A continuous. There is
an equivalent of about 1 to 1.5 squares of 1-ounce
copper between the input and output turret terminals.
Kelvin sensing is located under the center R5 position.
If using 1 resistor, put it in the middle; if using 2 resis-
tors (ideally equal value) put them in the outside posi-
tions; if using a high value resistor to "trim" a low value
unit, put the low value component in the middle and
the high value component on the outside.
Q1 is best removed with two large, hot soldering irons,
such as a Weller WTCPS controlled temperature iron
with a PTE8 tip. First cut the leads (or desolder and
lift), then apply the heat along Q1's tab shear line, and
pluck the part from the board using a pliers and a third
hand, immediately removing the soldering irons. Tab
removal should take only a few seconds.