MAX17005B/MAX17006B/MAX17015B
1.2MHz, Low-Cost,
High-Performance Chargers
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Applications Information
Setting Input Current Limit
The input current limit should be set based on the cur-
rent capability of the AC adapter and the tolerance of
the input current limit. The upper limit of the input cur-
rent threshold should never exceed the adapter’s mini-
mum available output current. For example, if the
adapter’s output current rating is 5A ±10%, the input
current limit should be selected so that its upper limit is
less than 5A × 0.9 = 4.5A. Since the input current-limit
accuracy of the MAX17005B/MAX17006B/MAX17015B
is ±3%, the typical value of the input current limit should
be set at 4.5A/1.03 ≈ 4.36A. The lower limit for input cur-
rent must also be considered. For chargers at the low
end of the specification, the input current limit for this
example could be 4.36A × 0.95 or approximately 4.14A.
Layout and Bypassing
Bypass DCIN with a 0.1µF ceramic capacitor to ground
(Figure 1). N1 and N2 protect the MAX17005B/
MAX17006B/MAX17015B when the DC power source
input is reversed. Bypass V
AA
, CSSP, and LDO as shown
in Figure 1.
Good PCB layout is required to achieve specified noise
immunity, efficiency, and stable performance. The PCB
layout designer must be given explicit instructions—
preferably, a sketch showing the placement of the
power switching components and high current routing.
Refer to the PCB layout in the MAX17005B/MAX17006B/
MAX17015B Evaluation Kit for examples. A ground
plane is essential for optimum performance. In most
applications, the circuit is located on a multilayer
board, and full use of the four or more copper layers is
recommended. Use the top layer for high-current con-
nections, the bottom layer for quiet connections, and
the inner layers for an uninterrupted ground plane.
Use the following step-by-step guide:
1) Place the high-power connections first, with their
grounds adjacent:
a) Minimize the current-sense resistor trace lengths,
and ensure accurate current sensing with Kelvin
connections.
b) Minimize ground trace lengths in the high-current
paths.
c) Minimize other trace lengths in the high-current
paths.
d) Use > 5mm wide traces in the high-current
paths.
e) Connect C
IN
to high-side MOSFET (10mm max
length).
f) Minimize the LX node (MOSFETs, rectifier cath-
ode, inductor (15mm max length)). Keep LX on
one side of the PCB to reduce EMI radiation.
Ideally, surface-mount power components are flush
against one another with their ground terminals
almost touching. These high-current grounds are
then connected to each other with a wide, filled
zone of top-layer copper, so they do not go through
vias. The resulting top-layer subground plane is
connected to the normal inner-layer ground plane
at the paddle. Other high-current paths should also
be minimized, but focusing primarily on short
ground and current-sense connections eliminates
approximately 90% of all PCB layout problems.
2) Place the IC and signal components. Keep the
main switching node (LX node) away from sensitive
analog components (current-sense traces and V
AA
capacitor). Important: The IC must be no further
than 10mm from the current-sense resistors. Quiet
connections to V
AA
and CC should be returned to a
separate ground (GND) island. There is very little cur-
rent flowing in these traces, so the ground island
need not be very large. When placed on an inner
layer, a sizable ground island can help simplify the
layout because the low-current connections can be
made through vias. The ground pad on the backside
of the package should also be connected to this
quiet ground island.
3) Keep the gate drive traces (DHI and DLO) as short
as possible (L < 20mm), and route them away from
the current-sense lines and V
AA
. These traces
should also be relatively wide (W > 1.25mm).
4) Place ceramic bypass capacitors close to the IC.
The bulk capacitors can be placed further away.
Place the current-sense input filter capacitors under
the part, connected directly to the GND pin.
5) Use a single-point star ground placed directly
below the part at the PGND pin. Connect the power
ground (ground plane) and the quiet ground island
at this location.
