LTC1433 データシートの表示（PDF） - Linear Technology
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LTC1433 Datasheet PDF : 20 Pages
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LTC1433/LTC1434
W
FUNCTIONAL DIAGRA
POR
LBO
SVIN
SHDN
PLL
PLL LPF
COSC
VCO
OSC
LOBAT
LBI
0.6V
VREF
+
FREQ
SHIFT
LIDET
–
PLLIN
50k
ITH
VREF
GM
180k
POR
RUN/SS 30k
6V
+
OVDET
–
VREF + 89mV
SHDN REF
AND
SVIN
VCC
VREF (1.19V)
VCC
PGND
SGND
CK Q
FF1
DQ
SLOPE
COMP
PWRVIN
RSENSE
0.143Ω
BSW
SSW
SB Q
FF2
RB Q
SB Q
FF3
RB Q
SHDN
VSET
IPEAK
DET
ICOMP
12mV
VOLTAGE
SELECT
120k 60k 240k
VPROG
60k
VOSENSE
1433/34 FD
U
OPERATION (Refer to Functional Diagram)
Main Control Loop
The LTC1433/LTC1434 is a constant frequency, pulse-
width modulated current mode switching regulator. Dur-
ing normal operation, the internal P-channel power MOSFET
is turned on each cycle when the oscillator sets the RS
latch FF3, and turned off when the main current compara-
tor ICOMP resets the latch. The peak inductor current at
which the ICOMP resets the RS latch is controlled by the
voltage on the ITH pin , which is the output of error amplifier
GM. Pins VPROG and VOSENSE, described in the Pin Func-
tions section, allow GM to receive an output feedback
voltage VFB from either the internal or external resistive
dividers. When the load current increases, it causes a
slight decrease in VFB relative to the 1.19V reference,
which in turn causes the ITH voltage to increase until the
average inductor current matches the new load current.
The main control loop is shut down by pulling the RUN/SS
pin low. Releasing RUN/SS allows an internal 3µA current
source to charge up the soft start capacitor CSS. When CSS
reaches 1.3V, the main control loop is enabled with the ITH
voltage clamped at approximately 30% of its maximum
value. As CSS continues to charge, ITH is gradually re-
leased allowing normal operation to resume.
Comparator OVDET guards against transient overshoots
> 7.5% by turning off the P-channel power MOSFETs and
keeping them off until the fault is removed.
Low Current Operation
The LTC1433/LTC1434 have two internal P-channel
MOSFETs sized for low and high load current conditions.
At low load current, only the small MOSFET will be turned
on while at high load current both MOSFETs will be on.
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