Datasheet

OSCin
DC
Blocking
Capacitor
Signal Generator
Semiconductor
Parameter
Analyzer
SMA Cable
10 MHz
Device
Under
Test
Evaluation Board
SMA Cable
Power Supply
3.3 V
CPout
Pin
LMX2541SQ2060E, LMX2541SQ2380E
LMX2541SQ2690E, LMX2541SQ3030E
LMX2541SQ3320E, LMX2541SQ3740E
SNOSB31I –JULY 2009–REVISED FEBRUARY 2013 www.ti.com
BENCH TEST SETUPS
Charge Pump Currents Test Setup
The charge pump is tested in external VCO mode (MODE=1), although it is no external VCO hooked up. The
CPout pin should be disconnected from the any external VCO tuning pin, external loop filter, and also the Vtune
pin on the device. A signal is then applied to the OSCin pin to ensure that the R counter is oscillating. This signal
does not have to be clean and the frequency is very critical. These currents at the CPout pin are typically
measured with a semiconductor parameter analyzer.
Charge Pump Current Measurements
In order to test the TRI-STATE current, the CPT bit is set to one and the current is measured. Aside from having
no other sources of leakage attached to this pin, it is also important that the board be well cleaned before doing
this test. The temperature and voltage at the charge pump can then be varied and the resulting leakage current
is then recorded. Typically, the leakage currents are worst at higher temperatures and higher charge pump
voltages.
In order to test the source and sink currents, the CPT bit is set to active mode and the frequency is programmed
to something much higher than can be achieved in order to force the charge pump to rail. The reason why this is
necessary is that the duty cycle of the charge pump is not 100% unless it is forced against one of the rails. If the
charge pump polarity bit (CPP) is set to positive, then the charge pump source current is measured. To measure
the sink current, the CPT bit is set to negative. The part is then programmed and the charge pump will rail in one
direction. The semiconductor parameter analyzer measures the current at a particular charge pump voltage. The
phase detector polarity bit, CPP, can be toggled to test between the negative and positive charge pump gains. In
order to test leakage, set the TRI-STATE bit, CPT, to 1 so that this can be measured. For the most accurate
measurements, it is desirable that the CPout and Vtune pin are not shorted together for these measurements.
Once these currents are measured, then the datasheet parameters can be calculated.
A summary of these charge pump tests is given in the table below.
Measurement PLL_R PLL_N CPG CPT CPP
Leakage Current X X X 1 (TRI-STATE) X
Source Current 1 4000 0 - 31 0 (Active) 1 (Positive)
Sink Current 1 4000 0 - 31 0 (Active) 0 (Negative)
26 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated
Product Folder Links: LMX2541SQ2060E LMX2541SQ2380E LMX2541SQ2690E LMX2541SQ3030E
LMX2541SQ3320E LMX2541SQ3740E