Datasheet
LTC3863
28
3863f
For more information www.linear.com/3863
APPLICATIONS INFORMATION
Table 2
FAILURE MODE V
OUT
I
OUT
I
VIN
f
RECOVERY
WHEN
FAULT IS
REMOVED? BEHAVIOR
None –5V 1A 453mA 350kHz N/A Normal Operation.
Pin Open
Open Pin 1 (PLLIN/MODE) –5V 1A 453mA 350kHz OK Pin already left open in normal application, so no difference.
Open Pin 2 (FREQ) –5V 1A 453mA 535kHz OK Frequency jumps to default open value.
Open Pin 3 (GND) –5V 1A 453mA 350kHz OK Exposed pad still provides GND connection to
device.
Open Pin 4 (SS) –5V 1A 453mA 350kHz OK External soft-start removed, but internal soft-start still available.
Open Pin 5 (V
FB
) 0V 0A 0.7mA 0kHz OK Controller stops switching. V
FB
internally self biases HI to prevent
switching.
Open Pin 6 (ITH) –5V 1A 507mA 40kHz OK Output still regulating, but the switching is erratic. Loop not stable.
Open Pin 7 (V
FBN
) –6V pk 1A 502mA 350kHz OK Use a 5.1V Zener V
Z
, 10k R
Z
and 0.01µF C
Z
. Output Voltage is –6V
peak and averages –4.9V.
Open Pin 8 (RUN) –5V 1A 453mA 350kHz OK Controller does not start-up.
Open Pin 9 (CAP) –5V 1A 453mA 350kHz OK More jitter during switching, but regulates normally.
Open Pin 10 (SENSE) 0V 0A 0.7mA 0kHz OK SENSE internally prebiases to 0.6V below V
IN
. This prevents
controller from switching.
Open Pin 11 (
V
IN
) –5.4V 1A 597mA 20kHz OK V
IN
able to bias internally through SENSE. Regulates with high
V
OUT
ripple.
Open Pin 12 (GATE) 0V 0A 0.7mA 0kHz OK Gate does not drive external power FET, preventing output
regulation.
Open Pin 13 (PGND) –5V 453mA 350kHz OK Pin 3 (GND) still provides GND connection to device.
Pins Shorted
Short Pins 1, 2
(PLLIN/MODE and FREQ)
–5V 1A 453mA 350kHz OK Burst Mode operation
disabled, but runs normally as in pulse-
skipping mode.
Short Pins 2, 3
(FREQ and GND)
–5V 1A 453mA 0kHz OK FREQ already shorted to GND, so regulates normally.
Short Pins 3, 4
(GND and SS)
0V 0A 0.7mA 0kHz OK SS short to GND prevents device from starting up.
Short Pins 4, 5
(SS and V
FB
)
–1V(DC)
–3V
P-P
50mA 9mA Erratic OK V
OUT
oscillates from 0V to 3V.
Short Pins 5, 6
(V
FB
and ITH)
–3.15V 625mA 181mA 350kHz OK Controller loop does not regulate to proper output voltage.
Short Pins 7, 8
(V
FBN
and RUN)
5V 0A 860µA 350kHz OK Controller does not start-up.
Short Pins 8, 9
(RUN and CAP)
–5V 1A 453mA 350kHz OK Able to start-up and regulate normally.
Short Pins 9, 10
(CAP and SENSE)
0V 0A 181mA 0kHz OK CAP ~
V
IN
, which prevents turning on external P-MOSFET.
Short Pins 10, 11
(SENSE and V
IN
)
–5V 1A 453mA 50kHz OK Regulates with high V
OUT
ripple.
Short Pins 11, 12
(V
IN
and GATE)
0V 0A 29mA 0kHz OK Power MOSFET is always kept OFF, preventing regulation.