lt3070 Linear Technology Corporation, lt3070 Datasheet - Page 18

• Manufacturer Part Number: lt3070
• Description: 5a, Low Noise, Programmable Output, 85mv Dropout Linear Regulator
• Manufacturer: Linear Technology Corporation

ApplicAtions inFormAtion
LT3070
PWRGD—Power Good
PWRGD pin is an open-drain NMOS digital output that
actively pulls low if any one of these fault modes is de-
tected:
• V
• V
• V
• The OUT-to-IN reverse-current detector activates.
• Junction temperature exceeds 145°C typically.*
*The junction temperature detector is an early warning
Stability and Output Capacitance
The LT3070’s feedback loop requires an output capacitor
for stability. Choose C
proximity to the LT3070’s OUT and GND pins. Include wide
routing planes for OUT and GND to minimize inductance.
If possible, mount the regulator immediately adjacent to
the application load to minimize distributed inductance
for optimal load transient performance. Point-of-Load
applications present the best case layout scenario for
extracting full LT3070 performance.

edge of V
25µs.
indicator that trips approximately 20°C before thermal
shutdown engages.
OUT
OUT
BIAS
is less than 90% of V
drops below 86% of V
is less than its undervoltage lockout threshold.
OUT
.
OUT
REF
carefully and mount it in close
SWITCHING REGULATOR
OUT(NOMINAL)
OUT(NOMINAL)
+
–
PWM
Figure 2. VIOC Control Block Diagram
for more than
on the rising
I
FB
TH
Low ESR, X5R or X7R ceramic chip capacitors are the
LTC recommended choice for stabilizing the LT3070. Ad-
ditional bulk capacitors distributed beyond the immediate
decoupling capacitors are acceptable as their parasitic ESL
and ESR, combined with the distributed PCB inductance
isolates them from the primary compensation pole provided
by the local surface mount ceramic capacitors.
The LT3070 requires a minimum output capacitance of
15µF for stability. LTC strongly recommends that the output
capacitor network consist of several low value ceramic
capacitors in parallel.
Why Do Multiple, Small-Value Output Capacitors
Connected in Parallel Work Better?
The LT3070’s unity-gain bandwidth with C
about 1MHz at its full-load current of 5A. Surface mounted
MLCC capacitors have a self-resonance frequency of
f
than the regulator bandwidth. Standard MLCC capacitors
are acceptable. To keep the resonant frequency greater
than 1MHz, the product 1/(2π√LC) must be greater than
1MHz. At this bandwidth, PCB vias can add significant
inductance, thus the fundamental decoupling capacitors
must be mounted on the same plane as the LT3070.
Typical 0603 or 0805 case-size capacitors have an ESL of
~800pH and PCB mounting can contribute up to ~200pH.
Thus, it becomes necessary to reduce the parasitic
R
= 1/(2π√LC), which must be pushed to a frequency higher
IN
V
REFERENCE
REF
–
+
300mV
V
OUT
LT3070
+
VIOC
OUT
3070 F02
LOAD
OUT
of 15µF is
3070f