MAX649 Maxim, MAX649 Datasheet - Page 9

• Manufacturer Part Number: MAX649
• Description: 5V/3.3V/3V or Adjustable / High-Efficiency /
• Manufacturer: Maxim

inductor, and the control circuit adjusts the switch duty
cycle to maintain regulation without exceeding the
switch current capability (Figure 3a). This provides
excellent load-transient response and high efficiency.
In discontinuous-conduction mode (DCM), current
through the inductor starts at zero, rises to a peak
value, then ramps down to zero. Although efficiency is
still excellent, the output ripple increases slightly, and
the switch waveforms exhibit ringing (the self-resonant
frequency of the inductor). This ringing is to be expect-
ed and poses no operational problems.
The MAX649/MAX651/MAX652 are said to be in
dropout when the input voltage (V+) is low enough
that the output drops below the minimum output
voltage specification (see Electrical Characteristics ).
The dropout voltage is the difference between the
input and output voltage when dropout occurs.
See the Typical Operating Characteristics for the
Dropout Voltage vs. Load Current and Dropout Voltage
vs. Temperature graphs.
Figure 3a. MAX649 Continuous-Conduction Mode, Heavy
Load-Current Waveform (500mA/div)
V+ = 10V, I
CIRCUIT OF FIGURE 1, R1 = 150m
5V/3.3V/3V or Adjustable, High-Efficiency,
LOAD
_______________________________________________________________________________________
= 1.3A
Low I
2 s/div
Q
, Step-Down DC-DC Controllers
Dropout
0A
1.5A
1A
Figure 3b. MAX649 Light/Medium Load-Current Waveform
(500mA/div)
Figure 4. Adjustable-Output Operation
V
IN
V
REF
R2 = R3
V+ = 10V, I
CIRCUIT OF FIGURE 1, R1 = 100m
C3
0.1 F
3
4
= 1.5V
SHDN
REF
(
V
V
OUT
LOAD
REF
MAX649
MAX651
MAX652
GND
– 1
= 1.4A
)
8
OUT
EXT
CS
V+
FB
5 s/div
5
6
7
1
2
1N5820
0.1
R1
D1
P1
Si9430
0.1 F
C4
22 H
L1
330 F
R2
R3
150k
C2
100 F
C1
OUTPUT
2.5A
2.0A
1.5A
1.0A
0.5A
0A
@ 1.5A
9