MAX1674EUA+T Maxim Integrated Products, MAX1674EUA+T Datasheet - Page 7

• Manufacturer Part Number: MAX1674EUA+T
• Description: IC DC-DC CONV HI EFF 8-UMAX
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1674EUA+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V, Adj
• Current - Output: 420mA
• Frequency - Switching: 500kHz
• Voltage - Input: 0.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Power - Output: 330mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX1674/MAX1675/MAX1676 compact, step-up
DC-DC converters start up with voltages as low as 0.9V
and operate with an input voltage down to 0.7V.
Consuming only 16µA of quiescent current, these
devices offer a built-in synchronous rectifier that
reduces cost by eliminating the need for an external
diode and improves overall efficiency by minimizing
losses in the circuit (see Synchronous Rectification sec-
tion for details). The internal MOSFET resistance is typi-
cally 0.3Ω, which minimizes losses. The current limit of
the MAX1674 and MAX1675 are 1A and 0.5A, respec-
tively. The MAX1675’s lower current limit allows the use
of a physically smaller inductor in space-sensitive
applications. The MAX1676 features a circuit that elimi-
nates noise due to inductor ringing. In addition, the
MAX1676 offers a selectable current limit (0.5A or 1A)
for design flexibility.
A unique minimum-off-time, current-limited, pulse-fre-
quency-modulation (PFM) control scheme is a key fea-
ture of the MAX1674/MAX1675/MAX1676. This scheme
Figure 1. Simplified Functional Diagram
R4
R3
V
IN
(MAX1676)
100k
R2
CLSEL
SHDN
V
OUT
LBO
LBI
ONE-SHOT
MINIMUM
OFF-TIME
MAXIMUM
ON-TIME
ONE-SHOT
_______________________________________________________________________________________
TRIG
ONE-SHOT
Detailed Description
Q
Compact, Step-Up DC-DC Converters
Q
S
ONE-SHOT
High-Efficiency, Low-Supply-Current,
PFM Control Scheme
F/F
R
TRIG
Q
ERROR
AMPLIFIER
LOW-BATTERY
COMPARATOR
CURRENT-LIMIT
AMPLIFIER
combines the high output power and efficiency of a
pulse-width-modulation (PWM) device with the ultra-low
quiescent current of a traditional PFM
is no oscillator; a constant-peak-current limit in the
switch allows the inductor current to vary between this
peak limit and some lesser value. At light loads, the
switching frequency is governed by a pair of one-shots
that set a typical minimum off-time (1µs) and a typical
maximum on-time (4µs). The switching frequency
depends upon the load and the input voltage, and can
range up to 500kHz. The peak current of the internal N-
channel MOSFET power switch is fixed at 1A
(MAX1674), at 0.5A (MAX1675), or is selectable
(MAX1676). Unlike conventional pulse-skipping DC-DC
converters (where ripple amplitude varies with input
voltage), ripple in these devices does not exceed the
product of the switch current limit and the filter-capaci-
tor equivalent series resistance (ESR).
The internal synchronous rectifier eliminates the need
for an external Schottky diode, thus reducing cost and
board space. During the cycle off-time, the P-channel
MOSFET turns on and shunts the MOSFET body diode.
REFERENCE
MAX1674
MAX1675
MAX1676
EN
ZERO
CROSSING
AMPLIFIER
(MAX1676)
N
P
Synchronous Rectification
DAMPING
SWITCH
BATT
GND
OUT
REF
LX
FB
0.1µF
200Ω
22µH
R1
47µF
0.1µF
R5
R6
(Figure
1). There
47µF
V
OUT
V
IN
7