LT3686 LINER [Linear Technology], LT3686 Datasheet - Page 15

• Manufacturer Part Number: LT3686
• Manufacturer: LINER [Linear Technology]

ApplicAtions inForMAtion
Figure 7 shows the transient response of the LT3686 with
several output capacitor choices. The output is 3.3V. The
load current is stepped from 0.25A to 1A and back to 0.25A,
and the oscilloscope traces show the output voltage. The
upper photo shows the recommended value. The second
photo shows the improved response (less voltage drop)
resulting from a larger output capacitor and a phase lead
capacitor. The last photo shows the response to a high
performance electrolytic capacitor. Transient performance
is improved due to the large output capacitance.
FB
Figure 7. Transient Load Response of the LT3686 with Different Output Capacitors as the Load Current Is Stepped from 0.25A to 1A.
V
IN
= 12V, V
32.4k
10k
FB
FB
OUT
32.4k
10k
32.4k
10k
47pF
= 3.3V, L = 6.8µH , Frequency = 2MHz
+
22µF
3686 F07a
22µF
×2
3686 F07d
100µF
SANYO
4TPB100M
3686 F07g
V
V
V
OUT
OUT
OUT
500mA/DIV
500mA/DIV
500mA/DIV
50mV/DIV
50mV/DIV
50mV/DIV
V
V
V
OUT
OUT
OUT
AC
AC
AC
I
I
I
L
L
L
MODE < 0.4V
20µs/DIV
20µs/DIV
20µs/DIV
BOOST and BD Pin Considerations
Capacitor C3 and the internal boost diode are used to
generate a boost voltage that is higher than the input
voltage. In most cases a 0.22μF capacitor will work well.
Figure 8 shows two ways to arrange the boost circuit. The
BOOST pin must be at least 2.2V above the SW pin for
best efficiency. For outputs of 3V and above, the standard
circuit (Figure 8a) is best. For outputs less than 3V and
above 2.5V, place a discrete Schottky diode (such as the
3686 F07b
3686 F07e
3686 F07h
500mA/DIV
500mA/DIV
500mA/DIV
50mV/DIV
50mV/DIV
50mV/DIV
V
V
V
OUT
OUT
OUT
AC
AC
AC
I
I
I
L
L
L
MODE > 0.8V
20µs/DIV
20µs/DIV
20µs/DIV
LT3686

3686fa
3686 F07c
3686 F07f
3686 F07i