LTC3788 Linear Technology, LTC3788 Datasheet - Page 16

• Manufacturer Part Number: LTC3788
• Description: Dual Output Synchronous Boost Controller
• Manufacturer: Linear Technology

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LTC3788
APPLICATIONS INFORMATION
The Typical Application on the fi rst page is a basic
LTC3788 application circuit. LTC3788 can be confi gured
to use either inductor DCR (DC resistance) sensing or a
discrete sense resistor (R
choice between the two current sensing schemes is largely
a design trade-off between cost, power consumption and
accuracy. DCR sensing is becoming popular because it
does not require current sensing resistors and is more
power-effi cient, especially in high current applications.
However, current sensing resistors provide the most
accurate current limits for the controller. Other external
component selection is driven by the load requirement,
and begins with the selection of R
and inductor value. Next, the power MOSFETs are selected.
Finally, input and output capacitors are selected.
SENSE
The SENSE
rent comparators. The common mode input voltage range
of the current comparators is 2.5V to 38V. The current
sense resistor is normally placed at the input of the boost
controller in series with the inductor.
16
3788 F02a
+
and SENSE
LTC3788
+
(2a) Using a Resistor to Sense Current
and SENSE
SENSE
SENSE
INTV
BOOST
VBIAS
SGND
SW
BG
TG
CC
+
–
–
Pins
–
(OPTIONAL)
SENSE
pins are the inputs to the cur-
) for current sensing. The
SENSE
Figure 2. Two Different Methods of Sensing Current
(if R
SENSE
is used)
V
V
IN
OUT
The SENSE
tor. It draws ~200μA during normal operation. There is a small
base current of less than 1μA that fl ows into the SENSE
The high impedance SENSE
parators allow accurate DCR sensing.
Filter components mutual to the sense lines should be
placed close to the LTC3788, and the sense lines should
run close together to a Kelvin connection underneath the
current sense element (shown in Figure 1). Sensing cur-
rent elsewhere can effectively add parasitic inductance
and capacitance to the current sense element, degrading
the information at the sense terminals and making the
programmed current limit unpredictable. If DCR sensing
is used (Figure 2b), sense resistor R1 should be placed
close to the switching node, to prevent noise from coupling
into sensitive small-signal nodes.
PLACE C1 NEAR SENSE PINS
3788 F02b
LTC3788
(2b) Using the Inductor DCR to Sense Current
+
Figure 1. Sense Lines Placement with
Inductor or Sense Resistor
SENSE
SENSE
INTV
pin also provides power to the current compara-
BOOST
VBIAS
V
SGND
IN
SW
TG
BG
CC
+
–
NEXT TO THE CONTROLLER
INDUCTOR OR R
TO SENSE FILTER,
C1
(R1 || R2) • C1 =
R2
–
SENSE
input to the current com-
DCR
R1
L
R
DCR
L
SENSE(EQ)
3788 F01
INDUCTOR
= DCR •
V
V
IN
OUT
R1 + R2
R2
–
pin.
3788f