7
DEMO MANUAL DC094
DESIGN READY SWITCHER
OPERATIO
U
2.7V). The output current thus ramps up slowly, charging
the output capacitor. If Run/SS has been pulled all the way
to ground there is a delay before starting of approximately
500ms/µF, followed by an additional 500ms/µF to reach
full current. C
SS
= 0.1µF on this PC board.
Pulling the Run/SS pin below 1.3V puts the LTC1435 into
a low quiescent current shutdown (I
Q
< 20µA). The
Run/SS pin has an internal 6V Zener clamp (see the data
sheet for further information).
Component Manufacturers
Following is a partial list of component manufacturers
which can be used in LTC1435 applications. Using com-
ponents other than the ones supplied on the demonstra-
tion board will require careful analysis to verify that all
component specifications are not exceeded. Finally, re-
characterizing the circuit for efficiency is necessary.
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
MANUFACTURER DEVICE TELEPHONE FAX
AVX Capacitors (803) 448-9411 (803) 448-1943
Central Semiconductor Diodes (516) 435-1110 (516) 435-1824
Coilcraft Inductors (708) 639-6400 (708) 639-1469
Coiltronics Inductors (407) 241-7876 (407) 241-9339
Comm Con Connectors (818) 301-4200 (818) 301-4212
Dale Inductors/Sense Resistors (605) 665-9301 (605) 665-0817
International Rectifiers MOSFETs/Diodes (310) 322-3331 (310) 322-3332
IRC Sense Resistors (512) 992-7900 (512) 992-3377
KRL Sense Resistors (603) 668-3210 (603) 624-0634
Motorola MOSFETs/Diodes (602) 244-3576 (602) 244-4015
Murata-Erie Capacitors (770) 436-1300 (770) 436-3030
Sanyo Capacitors/MOSFETs (619) 661-6835 (619) 661-1055
[81] 0952-82-3959 [81] 0952-82-4655
Siliconix MOSFETs (800) 554-5565 (408) 970-3979
Sprague Capacitors (603) 224-1961 (603) 224-1430
Sumida Inductors (708) 956-0666 (708) 956-0702
[81] 03-3607-5111 [81] 03-3607-5144
TDK Inductors (708) 803-6100 [81] 03-3278-5358
When the SFB pin is left floating (no jumper installed at J1)
Burst Mode is enabled.
Do not apply an external voltage to
SFB (E4) when the jumper JP1 is installed!
Run/Soft Start Function
The Run/SS pin (E3) is a dual purpose pin which provides
the soft start function and a means to shut down the
LTC1435. Soft start reduces surge currents from V
IN
by
gradually increasing the internal current limit. Power
supply sequencing can also be accomplished using
this pin.
An internal 3µA current source charges up an external
capacitor C
SS.
When the voltage on Run/SS reaches 1.3V
the LTC1435 begins operating. As the voltage on Run/SS
continues to ramp from 1.3V to 2.4V, the internal current
limit is also ramped at a proportional linear rate. The
current limit begins at approximately 50mV/R
SENSE
(at
V
RUN/SS
= 1.3V) and ends at 150mV/R
SENSE
(V
RUN/SS
≤
