CC26xx Layout Considerations

CC26xx HW Training
Layout Considerations
Fredrik Kervel, Bluetooth Smart Applications
1
Reference Schematic
VDD_EB
VDDS Decoupling Capacitors
VDDS
Pin 11
Pin 28
C2
C3
C4
C6
C7
DNM
100nF
100nF
10uF
100nF
BLM18HE152SN1
2
1
FL1
Pin 18
DCDC_SW2
VDDS
VDDS
R1
100k
6
DIO_0
7
DIO_1
8
DIO_2
9
DIO_3
10
DIO_4
15
DIO_5/JTAG_TDO
DIO_6/JTAG_TDI16
20
DIO_7
21
DIO_8
22
DIO_9
23
DIO_10
24
DIO_11
25
DIO_12
26
DIO_13
27
DIO_14
nRESET
JTAG_TCK
JTAG_TMS
C20
100nF
19
14
13
12
C19
1uF
33
U1
DIO_0
DIO_1
DIO_2
DIO_3
DIO_4
DIO_5
DIO_6
DIO_7
DIO_8
DIO_9
DIO_10
DIO_11
DIO_12
DIO_13
DIO_14
RESET_N
JTAG_TCKC
JTAG_TMSC
VDDR
VDDS
VDDS2
VDDS_DCDC
VDDR
VDDR
DCDC_SW
RX_TX
RF_N
RF_P
X24M_P
X24M_N
X32K_Q2
X32K_Q1
L1
10uH
Place L1 and
C8 close to pin 17
10uF
100nF
C10
C16
100nF
DNM
C31
17 DCDC_SW
L21
2.4nH
3
2
1
RFN
6.8pF
A1
C21
1
2
1
1pF
1
L10
6.8nH
X24M_P
X24M_N
RFP
5
4
2
C11
VSS
CC2650F128RHB
1
L11
2.4nH
2
L12
2
1
C12 2nH
C13
DNM
1pF
L13
2nH
2
C14
R12
12pF
0
3
1
C15
2.4GHz
DNM
R12 and C15 for
antenna matching
Y2
24MHz
Y1
1
32.768kHz
Pin 32
2
DCOUPL
12pF
C9
RX_TX
1pF
C17
C8
VDDR
28
11
18
29
32
31
30
VDDR Decoupling Capacitors
Pin 29
1
3
C18
12pF
2
4
2
Reference Layout
• Follow the reference layout! 
• All reference designs are for 2-layer PCBs
– Thickness = 0.8 mm
– 4 (or more) layers is also ok
• Place the RF match close to the RF pins
• Solid ground plane
– No signal traces underneath the RF path!
– Ground return paths between the antenna / RFcomponents and CC26xx must be uninterrupted
– Keep as much signal- and power routing on the top
layer as possible
• Place decoupling caps as close to the VDD pins
as possible
– Ground return paths between decoupling caps and
CC26xx should be short and direct
• DC/DC-regulator must have a short and direct
ground connection to CC26xx
3
Reference Layout – Differential output
• Antenna match components
• Longer RF traces must have 50 ohm impedance
• Notice orientation of pi-filter layout
– Shunt components oriented opposite way to avoid
crosstalk
4
Reference Layout – Differential output
• Antenna match components
• Longer RF traces must have 50 ohm impedance
• Notice orientation of pi-filter layout
– Shunt components oriented opposite way to avoid
crosstalk
• No traces underneath the RF path
– Will increase the impedance of the RF ground return
paths and, even worse, create current loops
– May lead to reduced RF performance and spuriuos
emission
5
Reference Layout – Single ended output
6
Reference Layout – Everything else
• Make sure decoupling ground paths
are short and direct (low impedance)
• Make sure the DCDC switch ground
path is short and direct (low
impedance)
• Try to locate as much routing as
possible on the top layer in 2-layer
PCBs
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Reference Layout – Everything else
• Make sure decoupling ground paths
are short and direct (low impedance)
• Make sure the DCDC switch ground
path is short and direct (low
impedance)
• Try to locate as much routing as
possible on the top layer in 2-layer
PCBs
8
Reference Layout – Trace impedance
• For RF traces longer than a certain length the impedance should be controlled
• TXLine is a free tool for PCB trace impedance calculations
– http://www.awrcorp.com/products/optional-products/tx-line-transmission-line-calculator
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