LT1617ES5#TRM Linear Technology, LT1617ES5#TRM Datasheet - Page 6

• Manufacturer Part Number: LT1617ES5#TRM
• Description: IC DC/DC CONV INVERTING TSOT23-5
• Manufacturer: Linear Technology
• Type: Invertingr

Specifications of LT1617ES5#TRM

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adj to -34V
• Current - Output: 350mA
• Voltage - Input: 1.2 ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-5, TSOT-5, TSOP-5
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -
• Other names: LT1617ES5; LT1617ES5

APPLICATIO S I FOR ATIO
LT1617/LT1617-1
tor values are used. This overshoot can be beneficial as it
helps increase the amount of available output current for
smaller inductor values. This will be the peak current seen
by the inductor (and the diode) during normal operation.
For designs using small inductance values (especially at
input voltages greater than 5V), the current limit over-
shoot can be quite high. Although it is internally current
limited to 350mA, the power switch of the LT1617 can
handle larger currents without problem, but the overall
efficiency will suffer. Best results will be obtained when
I
400mA for the LT1617-1.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multilayer ceramic capacitors are the best choice, as they
have a very low ESR and are available in very small
packages. Their small size makes them a good companion
to the LT1617’s SOT-23 package. Solid tantalum capaci-
tors (like the AVX TPS, Sprague 593D families) or OS-CON
capacitors can be used, but they will occupy more board
area than a ceramic and will have a larger ESR. Always use
a capacitor with a sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close as
possible to the LT1617. A 4.7 F input capacitor is suffi-
cient for most applications. Table 2 shows a list of several
capacitor manufacturers. Consult the manufacturers for
more detailed information and for their entire selection of
related parts.
6
PEAK
is kept below 700mA for the LT1617 and below
U
U
Table 2. Recommended Capacitors
CAPACITOR TYPE
Ceramic
Ceramic
Ceramic
W
U
VENDOR
Taiyo Yuden
[phone]
www.t-yuden.com
AVX
[phone]
www.avxcorp.com
Murata
[phone]
www.murata.com
Diode Selection
For most LT1617 applications, the Motorola MBR0520
surface mount Schottky diode (0.5A, 20V) is an ideal
choice. Schottky diodes, with their low forward voltage
drop and fast switching speed, are the best match for the
LT1617. For higher output voltage applications the 30V
MBR0530 can be used. Many different manufacturers
make equivalent parts, but make sure that the component
is rated to handle at least 0.5A. For LT1617-1 applications,
a Phillips BAT54 or a Central Semiconductor CMDSH-3
works well.
Lowering Output Voltage Ripple
Using low ESR capacitors will help minimize the output
ripple voltage, but proper selection of the inductor and the
output capacitor also plays a big role. The LT1617 pro-
vides energy to the load in bursts by ramping up the
inductor current, then delivering that current to the load.
If too large of an inductor value or too small of a capacitor
value is used, the output ripple voltage will increase
because the capacitor will be slightly overcharged each
burst cycle. To reduce the output ripple, increase the
output capacitor value or add a 100pF feed-forward ca-
pacitor in the feedback network of the LT1617 (see the
circuits in the Typical Applications section). Adding this
small, inexpensive 100pF capacitor will greatly reduce the
output voltage ripple.