參數(shù)資料
型號: LTC3713EG
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: Low Input Voltage, High Power, No RSENSE Synchronous Buck DC/DC Controller
中文描述: 2 A SWITCHING CONTROLLER, 1900 kHz SWITCHING FREQ-MAX, PDSO24
封裝: PLASTIC, SSOP-24
文件頁數(shù): 10/24頁
文件大?。?/td> 325K
代理商: LTC3713EG
10
LTC3713
3713fa
switch cycle, turning on the switch. When the summation
of a signal representing switch current and a ramp gen-
erator (introduced to avoid subharmonic oscillations at
duty factors greater than 50%) exceeds the V
C
signal,
comparator A2 changes state, resetting the flip-flop and
turn
ing off the switch. More power is delivered to the
output as switch current is increased. The output voltage,
attenuated by external resistor divider R7 and R8, appears
at the V
FB2
pin, closing the overall loop. Frequency com-
pensation is provided internally by R
C
and C
C
. Transient
OPERATIOU
APPLICATIOU
A typical LTC3713 application circuit is shown in
Figure 1. External component selection is primarily de-
termined by the maximum load current and begins with
the selection of the sense resistance and power MOSFET
switches. The LTC3713 uses the on-resistance of the
synchronous power MOSFET for determining the induc-
tor current. The desired amount of ripple current and
operating frequency largely determines the inductor value.
Finally, C
IN
is selected for its ability to handle the large
RMS current into the converter and C
OUT
is chosen with
low enough ESR to meet the output voltage ripple and
transient specification.
Maximum Sense Voltage and V
RNG
Pin
Inductor current is determined by measuring the voltage
across a sense resistance that appears between the
SENSE
+
and SENSE
pins. The maximum sense voltage
is set by the voltage applied to the V
RNG
pin and is equal
to approximately (0.133)V
RNG
. The current mode control
loop will not allow the inductor current valleys to exceed
(0.133)V
RNG
/R
SENSE
. In practice, one should allow some
margin for variations in the LTC3713 and external com-
ponent values and a good guide for selecting the sense
resistance is:
W
U
U
R
V
I
OUT MAX
(
SENSE
RNG
=
10
)
An external resistive divider from INTV
CC
can be used to
set the voltage of the V
RNG
pin between 0.5V and 2V
resulting in nominal sense voltages of 50mV to 200mV.
Additionally, the V
RNG
pin can be tied to SGND or INTV
CC
in which case the nominal sense voltage defaults to 70mV
or 140mV, respectively. The maximum allowed sense
voltage is about 1.33 times this nominal value.
Connecting the SENSE
+
and SENSE
Pins
The LTC3713 can be used with or without a sense resistor.
When using a sense resistor, it is placed between the
source of the bottom MOSFET M2 and ground. Connect
the
SENSE
+
and SENSE
pins as a Kelvin connection to the
sense resistor with SENSE
+
at the source of the bottom
MOSFET and the SENSE
pin to PGND1. Using a sense
resistor provides a well defined current limit, but adds cost
and reduces efficiency. Alternatively, one can eliminate the
sense resistor and use the bottom MOSFET as the current
sense element by simply connecting the SE
NSE
+
pin to the
drain and the SENSE
pin to the source of the bottom
MOSFET. This improves efficiency, but one must carefully
choose the MOSFET on-resistance as discussed in a later
section.
Applications Requiring Symmetric Current Limit
The I
TH
voltage has a range of 0V to 2.4V with 0.8V
corresponding to 0A. In applications in which the output
will only be sourcing current, this allows the output to sink
one third of the maximum source current. For applications
in which the output will be sourcing and sinking current,
it might be desirable to have a symmetrical output current
response can be optimized by the addition of a phase lead
capacitor C
PL
in parallel with R7 in applications where
large value or low ESR output capacitors are used.
As the load current is decreased, the switch turns on for
a shorter period each cycle. If the load current is further
decreased, the boost converter will skip cycles to main-
tain output voltage regulation. If the V
FB2
pin voltage is
increased significantly above 1.23V, the boost converter
will enter a low power state.
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