TECH SERIES Measurement Methods: DC Characteristics
the validity of the datasheet, it is often worthwhile to use a measurement matrix where the various combinations of load and input voltage can be compared.
As already mentioned, the electrical behavior of a DC / DC converter is determined by many different parameters that are specified in the data sheet. To quickly and efficiently characterize a converter and check
Test Test VINVIN
Table 3.1 shows a typical a measurement matrix setup.
IOUT IOUT VOUT VOUT
1 1 VIN,NOM V I IOUT,NOM VO1VO1 VININ,NOM OUT,NOM IOUT VOUT 2 2 VIN,NOM VIN,NOM IOUT,MIN IOUT,MIN VO2VO2
Test 1
V
V
VIN,MIN VV IN,MIN
VVO2 VO4 O4
VIN,MAX VIN,MAX
I
OUT,NOM 3 3 VIN,NOM VIN,NOM IOUT,MAX IOUT,MAX VO3VO1 IN,NOM O3
24 4 35 5
VVIN,NOM V
IOUT,MIN
IOUT,NOM IN,MIN IN,MIN IOUT,NOM
VVIN,NOM VVO3 VIN,MIN IIOUT,MIN IOUT,MIN VO5 OUT,MAX IN,MIN O5
VIN,MIN IIOUT,MAX IOUT,MAX VO6 4 6 6 VVIN,MIN VVO4 IN,MIN O6 OUT,NOM VIN,MAX IOUT,NOM IOUT,NOM VO7 IN,MAX O7 5 7 7 VVIN,MIN IOUT,MIN VVO5 VIN,MAX IOUT,MIN IOUT,MIN VO8VO8 IN,MAX 6 8 8 VVIN,MIN IOUT,MAX VO6
7 8
VIN,NOM VIN,NOM
nominal nominal Input Input Voltage Voltage
minimum Input Voltage minimum Input Voltage nominal Input Voltage IN,NOM maximum Input Voltage maximum Input Voltage
VIN,MIN
minimum Input Voltage
VIN,MAX
maximum Input Voltage
nominal Output Current Output Current IOUT,NOM IOUT,NOM nominal
minimum Output Current* Output Current* IOUT,MIN IOUT,MIN minimum
I
nominal Output Current
OUT,NOM maximum Output Current maximum Output Current IOUT,MAX IOUT,MAX
VIN,MAX
IOUT,NOM
VO7
minimum Output Current* IOUT,MIN Where Where „I „I “ can “ can be be ≼ 0% ≼ 0%
VIN,MAX
IOUT,MIN
VO8
IOUT,MAX
9 9 VIN,MAX VIN,MAX IOUT,MAX IOUT,MAX VO9VO9 Table 3.1: Measurement Matrix Table 3.1: Measurement Matrix
OUT,MIN OUT,MIN
Table 3.1.9Measurement WhereV“I VIN,MAX Matrix IOUT,MAX OUT, MIN � can be 0% O9
   Â
  Fig. 3.1: Measurement SetSet UpUp Fig. 3.1: Measurement
Where „IOUT,MIN“ can be ≼ 0%
   Â
Table 3.1: Measurement Matrix
maximum Output Current
 Â
To To obtain good and reliable measurement user should take a few basic obtain good and reliable measurement values, user should take a few basic thethe values, precautions on on how thethe measurements areare made. When preparing thethe testtest setset up,up, make precautions how measurements made. When preparing make
sure thatthat thethe contacts to the DC/DC converter have very lowlow resistance. Often measuring sure contacts to the DC/DC converter have very resistance. Often measuring terminals have variable contact resistances, so so thethe best testtest setup is ais"Kelvin" contact, terminals have variable contact resistances, best setup a "Kelvin" contact, as as shown above in Fig. 3.1, where current and thethe voltage paths areare connected shown above in Fig. 3.1, where the current and voltage paths connected Fig. 3.1: Measurement Setthe Up separately to to thethe pins. It isIt often tempting when using multimeters to to stack thethe 4mm separately pins. is often tempting when using multimeters stack 4mm Fig. 3.1. Measurement Set Up connectors in the meter sockets to connect up two or more meters, but this can lead connectors in the meter sockets to connect up two or more meters, but this can lead to basic To obtain good and reliable measurement values, the user should take a to few significant measurement errors. Each meter should be be separately connected to to thethe significant measurement errors. Each meter should separately connected precautions on how the measurements are made. When preparing the test set up, make converter pins as as shown above. converter pins shown above.
sure that the contacts to the DC/DC converter have very low resistance. Often measuring terminals have variable contact resistances, the best test can setup is aused, "Kelvin" To To load the DC/DC converter, power resistors orso power rheostats be be used, butbut it isit contact, load the DC/DC converter, power resistors or power rheostats can is as more shown above in Fig. 3.1, where the current and the voltage paths are connected elegant to use an an electronic load. However, some electronic loads need a minimum more elegant to use electronic load. However, some electronic loads need a minimum input voltage to regulate current properly, sowhen forfor converter voltages 4V,the input voltage topins. regulate the current properly, so converter output voltages below 4V, 4mm separately to the Ittheis often tempting using output multimeters tobelow stack often power resistors thethe only choice. Aup bench power supply makes a good often power resistors are only choice. A two bench power supply makes a can goodlead to connectors in the meterare sockets to connect or more meters, but this adjustable power supply, but make sure that it can deliver thethe necessary voltage and adjustable power supply, but make sure that it can deliver necessary voltage and to the significant measurement errors. Each meter should be separately connected current to cover all all of the input testtest requirements. It may be be necessary to combine several current to cover of the input requirements. It may necessary to combine several converter pins astoshown above. . The power supplies deliver V V . The power supplies to deliver current current limit limit must must be be setset so so that that there there is sufficient is sufficient IN,MAX IN,MAX
7