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MAX1832 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1832 Datasheet PDF : 12 Pages
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High-Efficiency Step-Up Converters with
Reverse Battery Protection
sometimes cause false shutdowns. To minimize the effect
of ripple, connect a low-value capacitor (C1) from SHDN
to GND to filter out input noise. Select a C1 value such
that the R4 C1 time constant is above 2ms.
Power-On Reset
The MAX1833/MAX1835 provide a power-on reset out-
put (RST). A 100kto 1Mpullup resistor from RST to
OUT provides a logic control signal. This open-drain
output pulls low when the output is 10% below its regu-
lation point. If not used, connect it to GND. RST is high
impedance in shutdown.
Setting the Output Voltage
The output voltage of the MAX1832/MAX1834 is
adjustable from +2V to +5.5V, using external resistors
R1 and R2 (Figure 1b). Since FB leakage is 20nA
(max), select feedback resistor R1 to be 100kto
1M. Calculate R2 as follows:
R2
=
R1
⎝⎜
VOUT
VFB
1⎠⎟
where VFB = 1.228V.
Inductor Selection
The control scheme of the MAX1832–MAX1835 permits
flexibility in choosing an inductor. A 10µH inductor per-
forms well for most applications, but values from 4.7µH to
100µH may also be used. Small inductance values typi-
cally offer smaller physical size. Large inductance values
minimize output ripple but reduce output power. Output
power is reduced when the inductance is large enough to
prevent the maximum current limit (525mA) from being
reached before the maximum on-time (5µs) expires.
For maximum output current, choose L such that:
( ) ( ) VBATT(MAX) 1µs < L < VBATT(MIN) 5µs
0.525A
0.525A
( ) IOUT(MAX) =
0.525A
2
×
VBATT(MIN)
0.525A
2
VOUT
RNCH + RIND
where RIND is the inductor series resistance, and RNCH
is the RDS(ON) of the N-channel MOSFET (0.4typ).
Capacitor Selection
Choose an output capacitor to achieve the desired out-
put ripple percentage.
COUT
>
0.5 × L × 0.525A2
r% × VOUT2
where r is the desired output ripple in %. A 10µF ceramic
Table 1. Suggested Inductors and
Suppliers
MANUFACTURER
Coilcraft
Sumida
INDUCTOR
DS1608C-103
DO1606T-103
CDRH4D18-100
CR43-100
PHONE
847-639-6400
847-956-0666
Murata
LQH4N100K
814-237-1431
Table 2. Suggested Surface-Mount
Capacitors and Manufacturers
VALUE
(µF)
4.7 to
47
4.7 to
10
4.7 to
22
DESCRIPTION
594/595 D-
series tantalum
TAJ, TPS-
series tantalum
X7R ceramic
X7R ceramic
MANU-
FACTURER
Sprague
AVX
TDK
Taiyo Yuden
PHONE
603-224-1961
803-946-0690
847-390-4373
408-573-4150
capacitor is a good starting value. The input capacitor
reduces the peak current drawn from the battery and
can be the same value as the output capacitor. A larger
input capacitor can be used to further reduce ripple and
improve efficiency.
PC Board Layout and Grounding
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.
Chip Information
TRANSISTOR COUNT: 953
PROCESS: BiCMOS
_______________________________________________________________________________________ 9

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