Rainbow Electronics MAX1714A - Manual (Page 3)

Evaluates: MAX1714A
MAX1714A Evaluation Kit
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Table 4. Jumper JU4/JU5/JU6 Functions (Switching-Frequency Selection)
Table 5. Troubleshooting Guide
IMPORTANT: Don’t change the operating frequency without first recalculating component values because the frequency has a signifi-
cant effect on the preferred inductor value, peak current-limit level, MOSFET heating, PFM/PWM switchover point, output noise, efficien-
cy, and other critical parameters.
JUMPER SHUNT LOCATION FREQUENCY (kHz)
JU4, JU5, JU6 Off 300
JU4 On
TON PIN
Floating
JU5, JU6 Off
200
JU5 On
Connected to V CC
JU4, JU6 Off
450 Connected to REF
JU6 On
JU4, JU5 Off
600 Connected to AGND
Circuit won’t start when SHDN
and +5V bias supply are cycled.
Output overvoltage due to
shorted high-side MOSFET
Replace the MOSFET.
Output overvoltage due to load
recovery overshoot Reduce the inductor value, raise the switching frequency, or
add more output capacitance.
Overload condition
Remove the excessive load or raise the ILIM threshold by
changing R3/R9.
Broken connection, bad
MOSFET, or other
catastrophic problem
Troubleshoot the power stage. Are the DH and DL gate-
drive signals present? Is the 2V V
REF present?
On-time pulses are erratic or
have unexpected changes in
period.
VBATT power source has poor
impedance characteristic Add a bulk electrolytic bypass capacitor across the bench-
top power supply, or substitute a real battery.
Load-transient V OUT waveform
shows excess ringing.
OR
LX switching waveform exhibits
double-pulsing (pulses separat-
ed only by a 400ns min off-time).
Instability due to output
capacitors placed at the
feedback point
Add parasitic PC board trace resistance between the
feedback point and the output capacitor.
OR
Substitute a different capacitor type (OS-CONs, tantalums,
or aluminum electrolytics work well).
SYMPTOM POSSIBLE PROBLEM SOLUTION
Circuit won’t start when power is
applied. Power-supply sequencing: +5V
bias supply was applied first
Cycle SHDN by removing and reinstalling JU1.