MAX8569A Maxim Integrated Products, MAX8569A Datasheet - Page 8

• Manufacturer Part Number: MAX8569A
• Description: (MAX8569A / MAX8569B) 200mA Step-Up Converters
• Manufacturer: Maxim Integrated Products

200mA Step-Up Converters in 6-Pin
SOT23 and TDFN
The SHDN trip threshold of the MAX8569A/MAX8569B
can be used as an input voltage detector that disables
the IC when the battery voltage falls to a set level. The
SHDN trip threshold is 1.228V. Use a resistor-divider to
set the battery-detection voltage (R1 and R2 in Figure 1).
Select R2 between 100kΩ and 1MΩ to minimize battery
drain. Calculate R1 as follows:
where V
shuts down and V
can sometimes cause false shutdowns. To minimize the
effect of ripple, connect a low-value capacitor (C2)
from SHDN to GND to filter out input noise. Select a C2
value so the R1, C2 time constant is above 2ms.
The MAX8569B provides a power-on reset output (RST)
that goes high impedance when the output reaches 90%
of its regulation point. RST pulls low when the output is
below 90% of the regulation point. Connect a 100kΩ to
1MΩ pullup resistor from RST to OUT to provide a logic
control signal for a microprocessor. Connect RST to
GND when the reset function is not used.
The output of the MAX8569A is adjustable from 2V to
5.5V. Connect a resistor-divider from the output to ground
with FB connected to the center tap to set the desired
output voltage (R3 and R4, Figure 1). Select R4 between
100kΩ and 1MΩ. R3 is then calculated as follows:
where V
1.228V.
The control scheme of the MAX8569A/MAX8569B per-
mits flexibility in choosing an inductor. A 10µH inductor
performs well for most applications, but values from
4.7µH to 100µH can be used as well. Small inductance
values typically offer smaller physical size. Output
power is reduced when the inductance is large enough
to prevent the maximum current limit (780mA) from
being reached before the maximum on-time (5µs)
expires. For maximum output current, choose L so that:
8
I
OUT MAX
V
_______________________________________________________________________________________
BATT MAX
Setting the Output Voltage (MAX8569A)
(
(
0 78
OUT
OFF
.
)
Power-On Reset (
)
A
=
R1 = R2 x ((V
×
is the desired output voltage and V
is the battery voltage at which the part
R3 = R4 x ((V
0 78
1
.
µ
2
s
A
SHDN
<
×
L



V
<
BATT MIN
= 1.228V. Note that input ripple
V
OFF
BATT MIN
(
OUT
/ V
(
0 78
)
Low-Battery Cutoff
.
V
Inductor Selection
/ V
−
OUT
SHDN
)
A
RST, MAX8569B)
0 78
FB
×
.
2
5
) - 1)
A
µ
) - 1)
s
×
(
R
NCH
+
R
FB
L
)



is
where R
the R
Choose an output capacitor to achieve the desired out-
put ripple percentage.
where L is the inductor value and r is the desired output
ripple in %. A 22µF ceramic capacitor is a good start-
ing value.
The input capacitor reduces the peak current drawn
from the battery and can be the same value as the out-
put capacitor. A larger input capacitor can be used to
further reduce the input ripple and improve efficiency.
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
directly to the ground plane. A sample layout is avail-
able in the MAX8569A/MAX8569B evaluation kit to
speed designs.
PROCESS: BiCMOS
MAX8569AEUT
MAX8569BEUT
MAX8569AETT
MAX8569BETT
MAX8569BETT30
DS(ON)
PART
C
L
OUT
is the inductor series resistance and R
of the internal n-channel MOSFET (0.3Ω typ).
> (0.5 x L x 0.780A
PC Board Layout and Grounding
VOLTAGE
Adjustable
Adjustable
Fixed 3.3V
Fixed 3.3V
Fixed 3.0V
OUTPUT
Chip Information
Capacitor Selection
Selector Guide
2
) / (r% x V
PACKAGE
SOT23-6
SOT23-6
TDFN
TDFN
TDFN
PIN-
OUT
2
)
MARK
ABWK
NCH
ABWL
TOP
AJN
AJO
AJP
is