ZHCSDY3 May 2015 LMX2581E
PRODUCTION DATA.
Low noise regulators are generally recommended for the supply pins. It is OK to have one regulator supply the part, although it is best to put individual bypassing as shown in the Layout Guidelines for the best spur performance. The most noise sensitive components are the pullup components for the output buffers since supply noise here will directly go to the output. For purposes of bypassing, below is how the current consumption is approximately distributed through each pin. For this table, default mode is with internal VCO mode with one output buffer powered up with OUTx_PWR=15. External VCO mode assumes the VCO divider and output buffers are off.
PIN NUMBER | PIN NAME | CONDITION | ||
---|---|---|---|---|
DEFAULT MODE | DEFAULT MODE with VCO DIVIDER ENABLED |
EXTERNAL VCO MODE with OUTPUT BUFFER DISABLED |
||
Pin 6 | VccCP | 12 | 12 | 12 |
Pin 10 | VccPLL | 28 | 28 | 48 |
Pin 16 | VccBUF | 23 | 43 | 1 |
Pin 17 | VccVCO | 83 | 83 | 14 |
Pin 28 | VccDIG | 10 | 10 | 10 |
Pin 32 | VccFRAC | <<1 | <<1 | <<1 |
n/a | Output pullup component | 22 | 22 | 0 |
TOTAL | 178 | 198 | 85 |
The recommendation for the VregVCO and VbiasCOMP pins is a minimum of one 10 µF capacitor, but more capacitance is better. These pins have a bias voltage of about 2.5 V, which means that capacitors of smaller case size and voltage ratings can actually have far less capacitance the labeled value of the capacitor. If there is insufficient capacitance on these pins, then the VCO phase noise may be degraded. This degradation may vary with frequency and how insufficient the capacitance is, but for example, bench tests show a degradation of about 5 dB at 20 KHz offset for a 3 GHz carrier if these capacitors are reduced to 4.7 µF.