Datasheet

UG-229 Evaluation Board User Guide
Rev. 0 | Page 4 of 8
VIN TO VOUT RESISTANCE (RDS
ON
)
RDS
ON
can be measured using the configuration shown in
Figure 4. RDS
ON
is defined as the input-to-output voltage
differential divided by load current.
The voltmeter reading divided by the load current value gives
the equivalent RDS
ON
value. For more accurate measurements,
a second voltmeter can be used to monitor the input voltage
across the input capacitor. The input supply voltage may need to
be adjusted to account for IR drops, especially if large load currents
are used. Figure 3 shows a typical curve of RDS
ON
measurements
with different load currents.
Use the following steps to connect to a voltage source and
voltmeter:
1. Connect the negative terminal (−) of the voltage source to
one of the GND pads on the evaluation board.
2. Connect the positive terminal (+) of the voltage source to
the VIN pad of the evaluation board.
3. Connect a load between the VOUT pad and one of the
GND pads.
4. Connect the negative terminal (−) of the voltmeter to one
of the VOUT pad.
5. Connect the positive terminal (+) of the voltmeter to the
VIN pad.
The voltage source can now be turned on. If J1 is inserted
(connecting EN to VIN for automatic startup), the switch
powers up.
0
0.05
0.10
0.15
0.20
0.25
0.30
1.0 1.4 1.8 2.2 2.6 3.0 3.4
RDS
ON
(Ω)
V
IN
(V)
I
LOAD
= 10mA
I
LOAD
= 20mA
I
LOAD
= 50mA
I
LOAD
= 100mA
I
LOAD
= 200mA
I
LOAD
= 500mA
09561-003
Figure 3. RDS
ON
vs. Input Voltage, V
IN
VOLTAGE SOURCE
LOAD
VOLTMETER
1.99711
09561-004
Figure 4. RDS
ON
Measurement