LTC3788-1_1 LINER [Linear Technology], LTC3788-1_1 Datasheet - Page 14

• Manufacturer Part Number: LTC3788-1_1
• Description: 2-Phase, Dual Output Synchronous Boost Controller
• Manufacturer: LINER [Linear Technology]

LTC3788-1
APPLICATIONS INFORMATION
The Typical Application on the fi rst page is a basic
LTC3788-1 application circuit. LTC3788-1 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.
14
37881 F02a
LTC3788-1
Figure 1. Sense Lines Placement with
Inductor or Sense Resistor
V
(2a) Using a Resistor to Sense Current
IN
SENSE
SENSE
INTV
BOOST
VBIAS
SGND
SW
BG
TG
CC
NEXT TO THE CONTROLLER
+
–
INDUCTOR OR R
TO SENSE FILTER,
(OPTIONAL)
SENSE
SENSE
) for current sensing. The
SENSE
Figure 2. Two Different Methods of Sensing Current
(if R
37881 F01
SENSE
is used)
V
V
IN
OUT
PLACE C1 NEAR SENSE PINS
37881 F02b
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.
The SENSE
parator. It draws ~200μA during normal operation. There
is a small base current of less than 1μA that fl ows into
the SENSE
current comparators allow accurate DCR sensing.
Filter components mutual to the sense lines should be
placed close to the LTC3788-1, 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.
LTC3788-1
+
(2b) Using the Inductor DCR to Sense Current
and SENSE
SENSE
SENSE
INTV
BOOST
VBIAS
–
SGND
+
+
pin. The high impedance SENSE
SW
BG
TG
pin also provides power to the current com-
CC
and SENSE
+
–
–
C1
Pins
(R1 || R2) • C1 =
–
R2
pins are the inputs to the cur-
DCR
R1
L
DCR
R
L
SENSE(EQ)
INDUCTOR
–
= DCR •
input to the
V
V
IN
OUT
R1 + R2
37881fa
R2