Measuring Evaluation Board Performance; Changes To Figure 4 - Analog Devices ADP5034 User Manual

UG-439
VOUT1
VIN1
SW1
BUCK
FB1
AGND
R1
V = V + 1
OUT1 FB1
R2
Figure 2. BUCK1 External Output Voltage Setting
Setting the Output Voltage of the LDO Regulators
Each LDO output voltage is set through external resistor
dividers, as shown in Figure 3, for LDO1. The output voltage can
optionally be factory programmed to default values as indicated in
the ADP5034 data sheet. In this event, FB3 must be connected to
the top of the capacitor on VOUT3 by placing a 0 Ω resistor on
R , and leave R unpopulated. Refer to Table 2 for the
TOP BOT
corresponding 0 Ω resistor placements on R
VIN3
VOUT3
LDO1
FB3
R1
V = V
+ 1
OUT1 FB3
R2
Figure 3. LDO1 External Output Voltage Setting
External Resistor Divider Setting for Buck and LDO
Regulators
The ADP5034 TSSOP evaluation boards are supplied with fixed
resistor dividers with values chosen for a target output voltage.
Varying the resistor values of the resistor divider networks
varies the output voltage accordingly.
Table 2. External Resistor Dividers
Resistor Divider Buck 1
R RT1
TOP
R RB1
BOT

MEASURING EVALUATION BOARD PERFORMANCE

Measuring Output Voltage Ripple of Buck Regulators
To observe the output voltage ripple of Buck 1, place an oscillo-
scope probe across the output capacitor (COUT1) with the probe
ground lead at the negative (−) capacitor terminal and the probe
tip at the positive (+) capacitor terminal.
Set the oscilloscope to ac, 10 mV/division, and 2 μs/division
time base, with the bandwidth set to 20 MHz to prevent noise
from interfering with the measurements. It is also recommended
to shorten the ground loop of the oscilloscope probe to minimize
coupling. One way of measuring the output voltage ripple is to
solder a wire to the negative (−) capacitor terminal and wrap it
around the barrel of the probe, while the tip directly connects to
the positive (+) capacitor terminal, as shown on Figure 4.
L1
1µH
VOUT1
R1
C5
10µF
R2
per channel.
TOP
VOUT3
C7
1µF
R
TOP
R
BOT
Buck 2 LDO1 LDO2
RT2 RT3 RT4
RB2 RB3 RB4
Rev. A | Page 4 of 13
Evaluation Board User Guide
Figure 4. Measuring Output Voltage Ripple
Measuring the Switching Waveform of Buck Regulators
To observe the switching waveform with an oscilloscope, place
the oscilloscope probe tip at the end of the inductor with the probe
ground at GND. Set the oscilloscope to dc, 2 V/division, and
200 ns/division time base. When the MODE pin is set to high, the
buck regulators operate in forced PWM mode. When the MODE
pin is set to low and the load is above a predefined threshold, the
buck regulators operate in PWM mode. When the load current
falls below a predefined threshold, the regulator operates in PSM,
improving the light load efficiency. Typical PWM and PSM
switching waveforms are shown in Figure 5 and Figure 6.
T
VOUT2
1
I
SW
2
SW2
4
CH1 50.0mV CH2 500mA Ω
CH4 2.00V
Figure 5. Typical Waveforms, V
T
VOUT2
1
I
SW
2
SW2
4
CH1 50mV CH2 500mA Ω
B W
CH4 2.00V
Figure 6. Typical Waveforms, V
M 4.00µs A CH2 240mA
T 28.40%
= 3.3 V, I = 30 mA, PSM Mode
OUT2 OUT2
M 400ns A CH2 220mA
B W
T 28.40%
= 3.3 V, I = 30 mA, PWM Mode
OUT2 OUT2