参数资料
型号: LTC3783IFE#TR
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 1 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封装: 4.40 MM, PLASTIC, TSSOP-16
文件页数: 4/24页
文件大小: 250K
代理商: LTC3783IFE#TR
LTC3783
12
3783fb
OPERATION
a maximum total gate charge of 35nC (the temperature
coefcient of the gate charge is low).
IQ(TOT) = 1.2mA + 35nC 300kHz = 12mA
PIC = 12V 12mA = 144mW
TJ = 70°C + 110°C/W 144mW = 86°C
This demonstrates how signicant the gate charge current
can be when compared to the static quiescent current in
the IC.
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked when
operating in a continuous mode at high VIN. A tradeoff
between the operating frequency and the size of the power
MOSFET may need to be made in order to maintain a reli-
able IC junction temperature. Prior to lowering the operat-
ing frequency, however, be sure to check with the power
MOSFET manufacturers for the latest low QG, low RDS(ON)
devices. Power MOSFET manufacturing technologies are
continually improving, with newer and better-performing
devices being introduced almost monthly.
Output Voltage Programming
In constant voltage mode, in order to regulate the output
voltage, the output voltage is set by a resistor divider ac-
cording to the following formula:
VV
R
OUT
FBP
=+
1
2
1
where 0 ≤ VFBP ≤ 1.23V. The external resistor divider is
connected to the output as shown in Figure 4, allowing
remote voltage sensing. The resistors R1 and R2 are
typically chosen so that the error caused by the 500nA
input bias current owing out of the FBN pin during
normal operation is less than 1%, which translates to
a maximum R1 value of about 25k at VFBP = 1.23V. For
lower FBP voltages, R1 must be reduced accordingly to
maintain accuracy, e.g., R1 < 2k for 1% accuracy when
VFBP = 100mV. More accuracy can be achieved with lower
resistances, at the expense of increased dissipation and
decreased light load efciency.
A similar analysis applies to the VFBP resistive divider, if
one is used:
VV
R
RR
FBP
REF
=
+
3
34
where R3 is subject to a similar 500nA bias current.
LTC3783
R4
R3
RUN
PWMIN
ITH
SS
VREF
FBP
FBN
FREQ
SYNC
VIN
OV/FB
PWMOUT
ILIM
GATE
SENSE
INTVCC
GND
VIN
3V TO 36V
GND
VOUT
R2
R1
3783 F04
Figure 4. LTC3783 Boost Application
Programming Turn-On and Turn-Off Thresholds
with the RUN Pin
The LTC3783 contains an independent, micropower voltage
reference and comparator detection circuit that remains
active even when the device is shut down, as shown in
Figure 5. This allows users to accurately program an input
voltage at which the converter will turn on and off. The
falling threshold on the RUN pin is equal to the internal
reference voltage of 1.248V. The comparator has 100mV
of hysteresis to increase noise immunity.
The turn-on and turn-off input voltage thresholds are
programed using a resistor divider according to the fol-
lowing formulas:
VV
R
VV
IN OFF
IN ON
()
.
=+
=
1 248
1
2
1
1 348
1
2
1
+
R
The resistor R1 is typically chosen to be less than 1M.
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