MAX1796EUA Maxim Integrated Products, MAX1796EUA Datasheet - Page 11

• Manufacturer Part Number: MAX1796EUA
• Description: IC CONV DCDC W/SHUTDWN 8-UMAX
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1796EUA

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V, Adj
• Current - Output: 300mA
• Frequency - Switching: 500kHz
• Voltage - Input: 1 ~ 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: Contains lead / RoHS non-compliant

V
tor output goes high impedance.
For single-cell applications, LBI may be connected to
the battery. When V
increases to 0.925V (see Typical Operating Char-
acteristics).
Connect a pullup resistor of 100kΩ or greater from LBO
to OUT for a logic output. LBO is an open-drain output
and can be pulled as high as 6V regardless of the volt-
age at OUT. When LBI is below the threshold, the LBO
output is high impedance. If the low-battery comparator
is not used, ground LBI and LBO.
An inductor value of 22µH performs well in most appli-
cations. The MAX1795/MAX1796/MAX1797 will also
work with inductors in the 10µH to 47µH range. Smaller
inductance values typically offer a smaller physical size
for a given series resistance, allowing the smallest
overall circuit dimensions, but have lower output cur-
rent capability. Circuits using larger inductance values
exhibit higher output current capability, but are physi-
cally larger for the same series resistance and current
rating.
The inductor’s incremental saturation current rating
should be greater than the peak switch-current limit,
which is 0.25A for the MAX1795, 0.5A for the MAX1796,
and 1A for the MAX1797. However, it is generally
acceptable to bias the inductor into saturation by as
much as 20% although this will slightly reduce efficien-
cy. Table 1 lists some suggested components for typi-
cal applications.
The inductor’s DC resistance significantly affects effi-
ciency. Calculate the maximum output current
(I
(I
and
D =
Low Supply Current, Step-Up DC-DC Converters
TRIP
RIP
OUT(MAX)
I
RIP
) and duty cycle (D):
V
is the input voltage where the low-battery detec-
V
OUT
=
OUT
V
) as follows, using inductor ripple current
OUT
+
+






I
Applications Information
LIM
I
LIM
+




______________________________________________________________________________________
t
OFF
I
LIM
L
−
−
BATT
I
RIP
I
+
RIP
2
×
2
(
(



R
<1.0V>, the LBI threshold
R



PFET
PFET
(
R
(
R
PFET
Inductor Selection
PFET
+
2
+
−
L
L
+
ESR
ESR
R
L
NFET
ESR
)
)
−




V
)
BATT
−
+
V
BATT
L L
ESR
)
where: I
Table 1 lists suggested tantalum or polymer capacitor
values for typical applications. The ESR of both input
bypass and output filter capacitors affects efficiency
and output ripple. Output voltage ripple is the product
of the peak inductor current and the output capacitor
ESR. High-frequency output noise can be reduced by
connecting a 0.1µF ceramic capacitor in parallel with
the output filter capacitor. (See Table 2 for a list of sug-
gested component suppliers.)
Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the IC’s GND pin and
the ground leads of the input and output filter capaci-
tors less than 0.2in (5mm) apart. In addition, keep all
connections to the FB and LX pins as short as possible.
In particular, when using external feedback resistors,
locate them as close to FB as possible. To maximize
output power and efficiency and minimize output ripple
voltage, use a ground plane and solder the IC’s GND
pin directly to the ground plane.
I
OUT MAX
(
with True-Shutdown
V
I
R
(Ω) (typ 0.27Ω)
L
V
L = Inductor value in µH
t
D = Duty cycle
R
(Ω) (typ 0.17Ω)
I
RIP
LIM
OFF
OUT(MAX)
ESR
OUT
BATT
PFET
NFET
)
= Inductor ripple current (A)
= Device current limit (0.25A, 0.5A, or 1A)
= LX switch’s off-time (µs) (typ 1µs)
=
= ESR of Inductor (Ω) (typ 0.095Ω)
= Output voltage (V)
PC Board Layout and Grounding
= Input voltage (V)
= On-resistance of P-channel MOSFET
= On-resistance of N-channel MOSFET



I
LIM
= Maximum output current (A)
−
I
RIP
2



Capacitor Selection
(
1
−
D
)
11