AATIAN22 Datasheet, PDF (10/11 Pages) SiGe Semiconductor, Inc. – 3MHz Fast Transient 400mA Step-Down Converter

EV-139
AAT1149 EVAL: 3MHz Fast Transient
400mA Step-Down Converter
Test: Gain and Phase Margin (Loop Gain)
1. Break the feedback loop and insert a one-to-one isolation transformer between the broken original con-
nection. Configure the specified test equipment as shown in Figure 9.
2. Inject a signal from SOURCE OUT to the loop through the isolation transformer while monitoring the ratio
of CHA and CHB on the Network Analyzer.
3. Set the output current to heavy load while monitoring the LX node of the converter on the oscilloscope (to
obtain a good result the converter must be in continuous PWM mode).
4. Sweep the frequency from SOURCE OUT of the Network Analyzer from 10Hz to 1MHz and adjust the mag-
nitude of the injected signal (around 10mV to 100mV) in order to have a clean PWM waveform at the LX node.
5. Repeat the measurement for different V_IN, V_OUT, and I_LOAD.
VIN
ON/OFF
C2
4.7uF
3
IN
1 _EN
6
PGND
7
PGND
L1
1.8uH
50
4
Isolation
Broken
VOUT
LX
Transformer
Original
Connection
2
FB
5
AGND
C6
R1
Adj.
100pF
(Optional)
R2
59K
C1
4.7uF
8
PGND
Figure 9: AAT1149 Schematic Connection Diagram for Gain and Phase Margin.
10
EV-139.2007.08.1.0