MAX608 Maxim, MAX608 Datasheet - Page 7

• Manufacturer Part Number: MAX608
• Description: 5V or Adjustable / Low-Voltage / Step-Up DC-DC Controller
• Manufacturer: Maxim

Figure 2a. 5V Preset Output
The MAX608 is a BiCMOS, step-up, switch-mode pow-
er-supply controller that provides a preset 5V output, in
addition to adjustable-output operation. Its unique con-
trol scheme combines the advantages of pulse-frequen-
cy modulation (low supply current) and pulse-width
modulation (high efficiency with heavy loads), providing
high efficiency over a wide output current range, as well
as increased output current capability over previous
PFM devices. In addition, the external sense resistor
and power transistor allow the user to tailor the output
current capability for each application. Figure 1 shows
the MAX608 functional diagram. The device has a shut-
down mode that reduces the supply current to 5µA
max.
Figure 2 shows the standard application circuits. The
IC is powered from the output, and the input voltage
range is 1.8V to V
known as bootstrap operation). The voltage applied to
the gate of the external power transistor is switched
from V
The MAX608’s output voltage can be set to 5V by con-
necting FB to ground; it can also be adjusted from 3V
to 16.5V using external resistors. Use 1% external feed-
back resistors when operating in adjustable-output
mode (Figures 2b, 2c) to achieve an overall output volt-
age accuracy of ±5%.
0.1 F
_______________Detailed Description
C3
OUT
5
4
3
6
C2
0.1 F
REF
SHDN
FB
AGND
to ground.
MAX608
GND
OUT
2
7
_______________________________________________________________________________________
OUT
EXT
CS
(this configuration is commonly
1
8
22 H
V
L1
IN
= 2V
MMFT3055EL
N
R
50m
1N5817
SENSE
D1
150 F
C1
5V or Adjustable, Low-Voltage,
C4
200 F
V
OUT
@ 0.5A
= 5V
Step-Up DC-DC Controller
The MAX608 uses a proprietary current-limited PFM con-
trol scheme to provide high efficiency over a wide range
of load currents. This control scheme combines the ultra-
low supply current of PFM converters (or pulse skippers)
with the high full-load efficiency of PWM converters.
Figure 2b. 12V Output
Figure 2c. 3.3V Output
0.1 F
0.1 F
R2 = (R1)
V
R2 = (R1)
V
REF
REF
C3
C3
= 1.5V
= 1.5V
(
(
5
4
6
5
4
6
C2
0.1 F
C2
0.1 F
V
V
V
V
OUT
OUT
REF
REF
REF
SHDN
AGND
REF
SHDN
AGND
-1
-1
)
)
MAX608
MAX608
OUT
GND
OUT
GND
2
2
7
7
EXT
EXT
CS
CS
FB
FB
1
8
3
1
8
3
22 H
22 H
V
V
PFM Control Scheme
IN
L1
IN
L1
= 2V
= 2V
MMFT3055EL
58k
50k
SI6426
N
N
R
50m
R
50m
R1
R1
SENSE
SENSE
1N5817
1N5817
D1
D1
150 F
150 F
C1
C1
47pF
402k
60k
C5
R2
R2
C4
200 F
C4
200 F
V
V
OUT
OUT
@ 0.3A
@ 0.6A
= 12V
= 3.3V
7