MAX1637EEE Maxim Integrated Products, MAX1637EEE Datasheet - Page 15

• Manufacturer Part Number: MAX1637EEE
• Description: IC CTRLR MINI LV STPDWN 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1637EEE

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.1 ~ 5.5 V
• Current - Output: 3A
• Frequency - Switching: Adj to 350kHz
• Voltage - Input: 3.15 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

The exact inductor value is not critical and can be
freely adjusted to allow trade-offs among size, cost,
and efficiency. Lower inductor values minimize size
and cost, but reduce efficiency due to higher peak-
current levels. The smallest inductor value is obtained
by lowering the inductance until the circuit operates at
the border between continuous and discontinuous
mode. Further reducing the inductor value below this
crossover point results in discontinuous-conduction
operation, even at full load. This helps lower output filter
capacitance requirements, but efficiency suffers under
these conditions, due to high I
hand, higher inductor values produce greater efficien-
cy, but also result in resistive losses due to extra wire
turns—a consequence that eventually overshadows the
benefits gained from lower peak current levels. High
inductor values can also affect load-transient response
(see the V
section). The equations in this section are for continu-
ous-conduction operation.
Three key inductor parameters must be specified:
inductance value (L), peak current (I
resistance (R
constant, LIR, which is the ratio of inductor peak-to-
peak AC current to DC load current. A higher LIR value
allows lower inductance, but results in higher losses
and ripple. A good compromise is a 30% ripple-current
to load-current ratio (LIR = 0.3), which corresponds to a
peak inductor current 1.15 times higher than the DC
load current.
where ƒ = switching frequency (normally 200kHz or
300kHz), and I
The peak current can be calculated as follows:
The inductor’s DC resistance should be low enough
that R
efficiency performance. If a standard, off-the-shelf
inductor is not available, choose a core with an LI
ing greater than L x IPEAK
diameter wire that fits the winding area. For 300kHz
applications, ferrite-core material is strongly preferred;
for 200kHz applications, Kool-Mu
even powdered iron is acceptable. If light-load efficien-
cy is unimportant (in desktop PC applications, for
example), then low-permeability iron-powder cores can
Kool-Mu is a trademark of Magnetics, Inc.
L = V
I
PEAK
DC
LIR)
x I
OUT
= I
SAG
PEAK
x V
LOAD
(V
DC
OUT
IN(MAX)
equation in the Low-Voltage Operation
IN(MAX)
). The following equation includes a
< 100mV, as it is a key parameter for
______________________________________________________________________________________
+ [V
= maximum DC load current.
)]
OUT
- V
OUT
2
(V
and wind it with the largest
IN(MAX)
) / (V
2
R losses. On the other
®
IN(MIN)
(aluminum alloy) or
Inductor Value
- V
PEAK
OUT
Precision Step-Down Controller
x ƒ x I
) / (2 x ƒ x L
), and DC
OUT
2
rat-
x
Miniature, Low-Voltage,
be acceptable, even at 300kHz. For high-current appli-
cations, shielded-core geometries (such as toroidal or
pot core) help keep noise, EMI, and switching-
waveform jitter low.
The current-sense resistor value is calculated accord-
ing to the worst-case, low-current limit threshold volt-
age (from the Electrical Characteristics) and the peak
inductor current:
Use I
Value section. Use the calculated value of R
size the MOSFET switches and specify inductor satura-
tion-current ratings according to the worst-case high-
current-limit threshold voltage:
Low-inductance resistors, such as surface-mount metal
film, are recommended.
Connect low-ESR bulk capacitors directly to the drain
on the high-side MOSFET. The bulk input filter capaci-
tor is usually selected according to input ripple current
requirements and voltage rating, rather than capacitor
value. Electrolytic capacitors with low enough equiva-
lent series resistance (ESR) to meet the ripple-current
requirement invariably have sufficient capacitance val-
ues. Aluminum electrolytic capacitors, such as Sanyo
OS-CON or Nichicon PL, are superior to tantalum
types, which risk power-up surge-current failure, espe-
cially when connecting to robust AC adapters or low-
impedance batteries. RMS input ripple current (I
determined by the input voltage and load current, with
the worst case occurring at V
when V
V
20Ω resistor and bypassed to ground independently.
Place a 0.1µF capacitor between V
close to the supply pin as possible. A 4.7µF capacitor
is recommended between V
The output filter capacitor values are generally deter-
mined by the ESR and voltage-rating requirements,
rather than by actual capacitance requirements for loop
stability. In other words, the low-ESR electrolytic capac-
itor that meets the ESR requirement usually has more
output capacitance than is required for AC stability.
CC
and V
PEAK
IN
is 2 x V
R
I
I
PEAK
RMS
GG
SENSE
from the second equation in the Inductor
should be isolated from each other with a
= I
= 120mV / R
OUT
Current-Sense Resistor Value
Output Filter Capacitor Value
LOAD
= 80mV / I
:
/ 2
Input Capacitor Value
GG
PEAK
SENSE
IN
and PGND.
= 2 x V
CC
OUT
and GND, as
. Therefore,
SENSE
RMS
) is
15
to