DC1023A - Demo Manual

DC1023A
LT3505
QUICK START GUIDE
LT3505
1.2A, Step-down Switching Regulator in
3mm×3mm DFN
DESCRIPTION
Demo circuit DC1023A is a monolithic step-dow n DC/DC
sw itching regulator featuring the LT3505. The demo circuit is designed for 5V output from a 6V to 36V input.
The w ide input range of the LT3505 allow s a variety of
input sources. The typical sources are automotive batteries, w all adaptors and industrial supplies. The oscillator
can be programmed for high frequency operation allow ing the use of tiny, low cost external components or it
can be programmed for low er frequency operation to
maximize efficiency. The current mode control scheme
creates fast transient response and good loop stability.
The gate drive of the internal sw itch is boosted to a voltage that is higher than Vin to ensure saturation of the
sw itch. A charge pump consisting of a diode and capacitor on the demo board performs the boost function. The
SH DN pin can be used to set the part in shutdow n mode,
reducing the supply current to less than 2uA. The SH DN
pin can also be used to program soft start. In this mode,
the SH DN pin is driven through an external R C filter to
create a voltage ramp on this pin. The soft start function
reduces the input current surge during start-up. Cycle by
cycle current limit, frequency foldback and thermal shutdow n provide the protection against shorted outputs.
The LT3505 datasheet gives a complete description of
the part,operation and application information. The datasheet must be read in conjunction w ith this quick start
guide for demo circuit DC1023A.
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation.
Performance Summary ( TA = 25oC )
PAR AM ETER
Minimum Input Voltage
Maximum Input Voltage
O utput Voltage VOUT
Sw itching Frequency
Sw itching Frequency
Maximum O utput Current
Efficiency
Efficiency
Voltage R ipple
Voltage R ipple
CO N DITIO N
JP2 in 2.2MH z position
JP2 in 750kH z position
VIN =8~32V
VIN =12V,Iout=1A,Freq=750kH z
VIN =12V,Iout=1A,Freq=2.2MH z
VIN =12V,Iout=1A,Freq=2.2MH z
VIN =12V,Iout=1A,Freq=750kH z
VALU E
6V
36V
5.05V ±4%
2.2MH z ±10%
750kH z ±10%
1.0A
85.0%
83.3%
5mV
20mV
1
LT3505
QUICK START PROCEDURE
Demonstration circuit 1023 is easy to set up to evaluate
the performance of the LT3505. R efer to Figure 1 for
proper measurement equipment setup and follow the
procedure below :
NOTE. W hen measuring the input or output voltage ripple,care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
Vin or Vout and GND terminals. See Figure 2 for proper scope probe
technique.
3.
W ith pow er off,connect the input pow er supply to Vin
and G N D.
4.
Turn on the pow er at the input.
NOTE. Make sure that the input voltage does not exceed 36V.
5.
NOTE. Ifthere is no output,temporarily disconnect the load to make
sure that the load is not set too high.
6.
1.
Place JP1 on the R U N position.
2.
Place JP2 on the selected frequency
Check for the proper output voltages.
O nce the proper output voltage is established, adjust
the load w ithin the operating range and observe the
output voltage regulation,ripple voltage,efficiency and
other parameters.
Figure 1. Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output Ripple
2
LT3505
INPUT VOLTAGE
FREQUENCY FOLDBACK
W hen the FR EQ jumper (JP2) is selected as 750K, the
sw itching frequency is fixed at 750kH z w ithin 6V to
36V input voltage range.
W hen FR EQ jumper (JP2) is selected as 2.2M, the
sw itching frequency is 2.2MH z w ithin 6V to 16V input
voltage range. The sw itching frequency w ill be linearly
decreased w hen the input voltage increases. The input
voltage frequency foldback curve is show n in Figure 3.
2.5
Freq (MHz)
2
1.5
1
0.5
0
0
10
20
Vin (V)
30
40
Figure 3. Input Voltage Frequency Foldback
OUTPUT CAPABILITY
VO U T =5V
Vin (V)
6
8
32
36
750K
0.7
1
1
1
Io max (A)
2.2M
0.05
1
1
0.4
3
LT3505
4
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