MAX8743(2004) 데이터 시트보기 (PDF) - Maxim Integrated
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MAX8743
(Rev.:2004)
(Rev.:2004)
Maxim Integrated
MAX8743 Datasheet PDF : 27 Pages
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Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
VDD
5V INPUT
VDD
V+
VDD
PGND*
BST1
DH1
LX1
CS1
VDD
DL1
V+ 2V TO 28V
ILIM1
V+
ILIM2
VCC - 1V
0.5V
VCC - 1V
0.5V
MAX8743
PWM
CONTROLLER
(FIGURE 3)
PWM
CONTROLLER
(FIGURE 3)
VDD
V+
BST2
DH2
LX2
CS2
VDD
DL2
OUT1
FB1
UVP
OVP
TON
SKIP
PGOOD
ON1
ON2
Figure 2. Functional Diagram
FAULT1
OUT 2
FB2
VCC
2V REF
REF
AGND*
FAULT2
* IN THE MAX8743EEI, AGND AND PGND ARE INTERNALLY CONNECTED AND CALLED GND.
VDD
20Ω
For example, in the standard application circuit with
VOUT1 = 2.5V, VIN = 15V, and K = 2.96µs (Table 4),
switchover to pulse-skipping operation occurs at ILOAD
= 0.7A or about 1/6 full load. The crossover point
occurs at an even lower value if a swinging (soft-satu-
ration) inductor is used.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency are made by varying the
inductor value. Generally, low inductor values produce
a broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the
coil resistance remains fixed) and less output voltage
ripple. Penalties for using higher inductor values
include larger physical size and degraded load-tran-
sient response (especially at low input-voltage levels).
DC output accuracy specifications refer to the threshold
of the error comparator. When the inductor is in continu-
ous conduction, the output voltage has a DC regulation
higher than the trip level by 50% of the ripple. In discon-
tinuous conduction (SKIP = GND, light-load), the output
______________________________________________________________________________________ 13
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