MAX8731EVSYS Maxim Integrated, MAX8731EVSYS Datasheet - Page 30

• Manufacturer Part Number: MAX8731EVSYS
• Description: Battery Management SMBus Level 2 Battery Charger with Remote Sense
• Manufacturer: Maxim Integrated
• Series: MAX8731Ar

Specifications of MAX8731EVSYS

• Battery Type: Li-Ion, Li-Polymer, NiCd, NiMH, Lead Acid, Universal
• Output Voltage: 5.4 V
• Operating Supply Voltage: 8 V to 26 V
• Charge Safety Timers: Yes
• Operating Supply Current: 2 uA
• Product Type: Charge Management
• Temperature Monitoring: No
• Uvlo Start Threshold: 2.5 V
• Uvlo Stop Threshold: 100 mV

SMBus Level 2 Battery Charger with
Remote Sense
Good PC board layout is required to achieve specified
noise immunity, efficiency, and stable performance. The
PC board layout artist must be given explicit instruc-
tions—preferably, a sketch showing the placement of
the power-switching components and high-current rout-
ing. Refer to the PC board layout in the MAX8731 evalu-
ation kit for examples. A ground plane is essential for
optimum performance. In most applications, the circuit
will be located on a multilayer board, and full use of the
four or more copper layers is recommended. Use the
top layer for high-current connections, the bottom layer
for quiet connections, and the inner layers for uninter-
rupted ground planes.
Use the following step-by-step guide:
1) Place the high-power connections first, with their
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grounds adjacent:
a) Minimize the current-sense resistor trace
b) Minimize ground trace lengths in the high-cur-
c) Minimize other trace lengths in the high-current
d) Connect C1 and C2 to high-side MOSFET
e) Minimize the LX node (MOSFETs, rectifier cath-
f)
g) Ideally, surface-mount power components are
______________________________________________________________________________________
lengths, and ensure accurate current sensing
with Kelvin connections.
rent paths.
paths.
Use > 5mm wide traces in the high-current
paths.
(10mm max length). Place the input capacitor
between the input current-sense resistor and
drain of the high-side MOSFET.
ode, inductor (15mm max length)). Keep LX on
one side of the PC board to reduce EMI radiation.
Since the return path of DHI is LX, route DHI near
LX. Optimally, LX and DHI should overlap. The
same principle is applied to DLO and PGND.
flush against one another with their ground termi-
nals almost touching. These high-current
grounds are then connected to each other with a
wide, filled zone of top-layer copper, so they do
2) Place the IC and signal components. Keep the
3) Keep the gate-drive traces (DHI and DLO) as short
4) Place ceramic bypass capacitors close to the IC.
5) Use a single-point star ground placed directly
TRANSISTOR COUNT: 10,234
PROCESS: BiCMOS
main switching node (LX node) away from sensitive
analog components (current-sense traces and REF
capacitor).
Important: The IC must be no further than 10mm
from the current-sense resistors. Quiet connections
to REF, CCS, DAC, CCV, CCI, ACIN, and VCC
should be returned to a separate ground (GND)
island. The analog ground is separately worked
from power ground in Figure 1. There is very little
current 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 back-
side of the package should also be connected to
this quiet ground island.
as possible (L < 20mm), and route them away from
the current-sense lines and REF. These traces
should also be relatively wide (W > 1.25mm).
The bulk capacitors can be placed further away.
Place the current-sense input filter capacitors under
the part, connected directly to the GND pin.
below the part at the PGND pin. Connect the power
ground (ground plane) and the quiet ground island
at this location.
not go through vias. The resulting top-layer sub-
ground 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 PC board layout problems.
Chip Information