Datasheet
MAX2870
23.5MHz to 6000MHz Fractional/
Integer-N Synthesizer/VCO
16Maxim Integrated
Register and Bit Descriptions
The operating mode of the device is controlled by five on-chip registers.
Defaults are not guaranteed upon power-up and are provided for reference only. All reserved bits should only be writ-
ten with default values. In low-power mode, the register values are retained. Upon power-up, the registers should be
programmed twice with at least a 20ms pause between writes. The first write ensures that the device is enabled, and
the second write starts the VCO selection process.
Table 4. Register 0 (Address: 000, Default: 007D0000
HEX
)
Table 5. Register 1 (Address: 001, Default: 2000FFF9
HEX
)
BIT LOCATION BIT ID NAME DEFINITION
31 INT
Int-N or Frac-N
Mode Control
0 = Enables the fractional-N mode
1 = Enables the integer-N mode
The LDF bit must also be set to the appropriate mode.
30:15 N[15:0]
Integer Division
Value
Sets integer part (N-divider) of the feedback divider factor. All integer
values from 16 to 65,535 are allowed for integer mode. Integer values
from 19 to 4,091 are allowed for fractional mode.
14:3 FRAC[11:0]
Fractional
Division Value
Sets fractional value:
000000000000 = 0 (see F0I bit description)
000000000001 = 1
----
111111111110 = 4094
111111111111 = 4095
2:0 ADDR[2:0] Address Bits Register address bits
BIT LOCATION BIT ID NAME DEFINITION
31 CPOC
CP Output
Clamp
Sets charge-pump output clamp mode.
0 = Disables clamping of the CP output when the CP is off
1 = Enables the clamping of the CP output when the CP is off (improved
integer-N in-band phase noise)
30:29 CPL[1:0] CP Linearity
Sets CP linearity mode.
00 = Disables the CP linearity mode (integer-N mode)
01 = Enables the CP linearity mode (frac-N mode)
10 = Reserved
11 = Reserved
28:27 CPT[1:0]
Charge Pump
Test
Sets charge-pump test modes.
00 = Normal mode
01 = Reserved
10 = Force CP into source mode
11 = Force CP into sink mode
26:15 P[11:0] Phase Value
Sets phase value. See the Phase Shift Mode section.
000000000000 = 0
000000000001 = 1 (recommended)
-----
111111111111 = 4095