SP6641AEK-L-5-0/TR Exar Corporation, SP6641AEK-L-5-0/TR Datasheet - Page 8
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SP6641AEK-L-5-0/TR
Manufacturer Part Number
SP6641AEK-L-5-0/TR
Description
500mA Alkaline DC/DC Boost Regulator
Manufacturer
Exar Corporation
Type
Step-Up (Boost), PFMr
Datasheet
1.SP6641AEK-L-3-3.pdf
(13 pages)
Specifications of SP6641AEK-L-5-0/TR
Internal Switch(s)
Yes
Synchronous Rectifier
Yes
Number Of Outputs
1
Voltage - Output
5V
Current - Output
175mA
Voltage - Input
0.5 V ~ 4.5 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
SC-74A, SOT-753
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
SP6641AEK-L-5-0/TR
Manufacturer:
EXAR
Quantity:
5 064
APPLICATION INFORMATION
Circuit Layout
Printed circuit board layout is a critical part of a
power supply design. Poor designs can result in
excessive EMI on the voltage gradients and
feedback paths on the ground planes with appli-
cations involving high switching frequencies
and large peak currents. Excessive EMI can
result in instability or regulation errors. All
power components should be placed on the PC
board as closely as possible with the traces kept
short, direct, and wide (>50mils or 1.25mm).
Extra copper on the PC board should be inte-
grated into ground as a pseudo-ground plane.
On a multilayer PC board, route the star ground
using component-side copper fill, then connect
it to the internal ground plane using vias. For the
SP6641A/6641B devices, input and output fil-
ter capacitors should be soldered with their
ground pins as close together as possible in a
star-ground configuration. The VOUT pin must
be bypassed directly to ground as close to the
SP6641A/6641B devices as possible (within
0.2in or 5mm). The DC-DC converter and any
digital circuitry should be placed on the oppo-
site corner of the PC board as far away from
sensitive RF and analog input stages. Noisy
traces, such as from the LX pin, should be kept
away from the voltage-feedback VOUT node
and separated from it using grounded copper to
minimize EMI. See the SP6641A/6641B Evalu-
ation Board Manual for PC Board Layout de-
sign details.
Component Selection
Selection of capacitors, inductors and schottky
diodes for SP6641A and SP6641B power sup-
ply circuits can be made through the use of
Table 1 component selection. Capacitor equiva-
lent series resistance is a major contributor to
output ripple, usually greater than 60%. Low
ESR capacitors are recommended. Ceramic ca-
pacitors have the lowest ESR. Low-ESR tanta-
lum capacitors may be a more acceptable solu-
tion having both a low ESR and lower cost than
large ceramic capacitors. Designers should se-
lect input and output capacitors with a rating
exceeding the peak inductor current. Do not
Rev. 5/26/05, *Patent Pending
SP6641A/6641B 500mA Alkaline DC/DC Boost Regulator in SOT-23
8
allow tantalum capacitors to exceed their ripple-
current ratings. For example, in the SP6641A a
22µF, 6V, low-ESR, surface-mount tantalum
output filter capacitor typically provides 60mV
output ripple when stepping up from 1.3V to
3.3V at 20mA. An input filter capacitor can
reduce peak currents drawn from the battery and
improve efficiency. Low-ESR aluminum elec-
trolytic capacitors are acceptable in some appli-
cations but standard aluminum electrolytic ca-
pacitors are not recommended.
In selecting an inductor, the saturation current
specified for the inductor needs to be greater
then the SP6641A/B peak current to avoid satu-
rating the inductor, which would result in a loss
in efficiency and could damage the inductor.
The SP6641A evaluation board uses a Sumida
CDRH5D28 22µH inductor with an Isat value
of 0.9A and a DCR of 0.095Ω, which easily
handles the Ipeak of 0.33A of the SP6641A and
will deliver high efficiencies. The SP6641B
evaluation board uses a Sumida CDRH5D28
10µH inductor with an Isat value of 1.3A and a
DCR of 0.065Ω, which easily handles the Ipeak
of 1.0A of the SP6641B and will deliver high
efficiencies. Other inductors could be selected
provided their Isat is greater than the Ipeak of
the SP6641A/SP6641B.
Output Filter or LDO Regulator
Designers could add LC pi filters, linear post-
regulators, or shielding in applications necessary
to address excessive noise, voltage ripple, or EMI
concerns. The LC pi filter’s cutoff frequency should
be at least a decade or two below the DC-DC
converters’ switching frequency for the specified
load and input voltage. The SP6201, a small SOT23-
5pin 200mA Low Drop Out linear regulator can be
used at the SP6641A/6641B output to reduce
output noise and ripple. The schematic in figure 15
illustrates this circuit on the SP6641A Evaluation
Board with the SP6641 3.3V output followed by
the Sipex SP6201 3.0V output Low Drop Out
linear regulator.
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