LMX2485 National Semiconductor Corporation, LMX2485 Datasheet - Page 16

• Manufacturer Part Number: LMX2485
• Description: 50 Mhz - 3.0 Ghz High Performance Delta-sigma Low Power Dual Pllatinum 50 Mhz - 3.0 Ghz High Performance Delta-sigma Low Power Dual Pllatinum? Frequency Synthesizers With 800 Mhz Integer Pll
• Manufacturer: National Semiconductor Corporation

www.national.com
Bench Test Setups
Charge Pump Current Measurement Procedure
The above block diagram shows the test procedure for testing the RF and IF charge pumps. These tests include absolute current
level, mismatch, and leakage measurement. In order to measure the charge pump currents, a signal is applied to the high
frequency input pins. The reason for this is to guarantee that the phase detector gets enough transitions in order to be able to
change states. If no signal is applied, it is possible that the charge pump current reading will be low due to the fact that the duty
cycle is not 100%. The OSCin Pin is tied to the supply. The charge pump currents can be measured by simply programming the
phase detector to the necessary polarity. For instance, in order to measure the RF charge pump, a 10 MHz signal is applied to
the FinRF pin. The source current can be measured by setting the RF PLL phase detector to a positive polarity, and the sink
current can be measured by setting the phase detector to a negative polarity. The IF PLL currents can be measured in a similar
way. Note that the magnitude of the RF PLL charge pump current is controlled by the RF_CPG bit. Once the charge pump
currents are known, the mismatch can be calculated as well. In order to measure leakage, the charge pump is set to a TRI-STATE
mode by enabling the RF_CPT and IF_CPT bits. The table below shows a summary of the various charge pump tests.
RF TRI-STATE
IF TRI-STATE
Current Test
RF Source
IF Source
RF Sink
IF Sink
RF_CPG
0 to 15
0 to 15
X
X
X
X
RF_CPP
X
X
X
X
0
1
16
RF_CPT
0
0
1
X
X
X
IF_CPP
X
X
X
X
0
1
IF_CPT
20087769
X
X
X
0
0
1