LT3692_15 Datasheet, PDF (27/36 Pages) Linear Technology – Monolithic Dual Tracking 3.5A Step-Down Switching Regulator

LT3692
Applications Information
As a safeguard, the LT3692 has an additional thermal
shutdown threshold set at a typical value of 163°C for each
channel. Each time the threshold is exceeded, a power on
sequence for that channel will be initiated. The sequence
will then repeat until the thermal overload is removed.
It should be noted that the T_J pin voltage represents
a steady-state temperature and should not be used to
guarantee that maximum junction temperatures are
not exceeded. Instantaneous power along with thermal
gradients and time constants may cause portions of the
die to exceed maximum ratings and thermal shutdown
thresholds. Be sure to calculate die temperature rise for
steady state (>1Min) as well as impulse conditions.
CLKOUT Capacitive Loading
A minor drawback to generating a negative rail from the
CLKOUT pin is that the charge pump adds capacitance to
the CLKOUT pin, resulting in an output synchronization
clock signal phase delay. Figures 23 and 24 show the im-
pact of capacitive loading on the CLKOUT signal rise and
fall times. Note that a typical 10:1 150MHz oscilloscope
probe contributes significant capacitance to the CLKOUT
node, necessitating a low capacitance probe for accurate
measurements. Applications requiring CLKOUT to generate
the negative supply voltage and provide the synchroniza-
tion clock to other regulators may benefit from buffering
CLKOUT prior to the charge pump circuitry.
Other Linear Technology Publications
Application notes AN19, AN35 and AN44 contain more
detailed descriptions and design information for buck
regulators and other switching regulators. The LT1376
data sheet has a more extensive discussion of output
ripple, loop compensation and stability testing. Design
Note DN100 shows how to generate a dual (+ and –)
output supply using a buck regulator.
500mV/DIV
CHARGE PUMP
SCOPE PROBE: 15pF
SYNCHRONIZED LT3692
RT/SYNC PIN
FET PROBE: 2pF
CHARGE PUMP
500mV/DIV
FET PROBE: 2pF
SCOPE PROBE: 15pF
SYNCHRONIZED
LT3692 RT/SYNC PIN
40ns/DIV
FREQUENCY: 1.000MHz
3692 F23
Figure 23. CLKOUT Rise Time
20ns/DIV
FREQUENCY: 1.000MHz
3692 F24
Figure 24. CLKOUT Fall Time
For more information www.linear.com/3692
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