DEMO CIRCUIT 897
QUICK START GLT3U4ID93E
1.2A, 750KHz Step-down Switching Regulator
in 2mm×3mm DFN
Demonstration circuit 897 is a monolithic step-dow n the supply current to less than 2uA.The SH DN pin can
DC/DC sw itching regulator featuring the LT3493. The also be used to program soft start. In this mode, the
demo board is designed for 3.3V output from a 4.5V to SH DN pin is driven through an external R C filter to create
36V input.The w ide input range of the LT3493 allow s a a voltage ramp on this pin. The soft start function re-
variety ofinput sources.The typical sources are automo- duces the input current surge during start-up. Cycle by
tive batteries, w all adaptors and industrial supplies.The cycle current limit,frequency foldback and thermal shut-
750kH z sw itching frequency allow s the use ofsmall,low dow n provide protection against shorted outputs.
cost inductor and ceramic capacitors, resulting in low , The LT3493 datasheet gives a complete description of
predictable output ripple. The current mode control the part,operation and application information.The data-
scheme creates fast transient response and good loop sheet must be read in conjunction w ith this quick start
stability.The internal compensation reduces the compo- guide for demo circuit 897.
nent count and solution size.The gate drive ofthe inter-
nal sw itch is boosted to a voltage that is higher than the Design files for this circuit board are available. Call
Vin to ensure saturation of the sw itch. A charge pump the LTC factory.
consisting of diode and a capacitor on the demo board ,LTC and LT are registered trademarks ofLinear Technology Corporation.ThinSOT and
performs the boost function.The SH DN pin can be used Pow erPath are trademarks ofLinear Technology Corporation.
to set the part in micropow er shutdow n mode,reducing
Performance Summary ( TA = 25oC )
PAR AM ETER FO R LED DR IVER CO N DITIO N VALU E
Minimum input voltage 4.5V
Maximum input voltage 36V
O utput voltage VOUT 3.3V +/- 4%
Maximum output current VIN=4.5V 950mA
Maximum output current VIN=8V 1.2A
Typical sw itching frequency 750kH z
QUICK START PROCEDURE
Demonstration circuit 897 is easy to set up to evaluate 1. Place JP1 on the R U N position:
the performance of the LT3493. R efer to Figure 1 for 2. W ith pow er off,connect the input pow er supply to Vin
proper measurement equipment setup and follow the and G N D.
procedure below :
NOTE. W hen measuring the input or output voltage ripple,care must be 3. Turn on the pow er at the input.
taken to avoid a long ground lead on the oscilloscope probe.Measure the NOTE. Make sure that the input voltage does not exceed 36V.
input or output voltage ripple by touching the probe tip directly across the Check for the proper output voltages.
Vin or Vout and GND terminals.See Figure 2 for proper scope probe 4.
technique. NOTE. Ifthere is no output,temporarily disconnect the load to make
sure that the load is not set too high.
5. O nce the proper output voltages are established, ad- the output voltage regulation,ripple voltage, efficiency
just the loads w ithin the operating range and observe and other parameters.
+ _ _ V+
_ V _ + _
+ A + _ A +
Figure 1. Proper M easurem ent Equipm ent Setup
Figure 2. M easuring Input or Output Ripple
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