LTC3632_15 Datasheet, PDF(16/22 Page) Linear Technology – High Efficiency, High Voltage 20mA Synchronous Step-Down Converter

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LTC3632_15 Datasheet, PDF (16/22 Pages) Linear Technology – High Efficiency, High Voltage 20mA Synchronous Step-Down Converter

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LTC3632

APPLICATIONS INFORMATION

The undervoltage lockout requirement on VIN can be

satisfied with a resistive divider from VIN to the RUN and

HYST pins. Choose R1â¯=â¯2M and calculate R2 and R3 as

follows:

ï£«

ï£¬ï£¬

ï£

1.21V

VIN(RISING) â

1.21V

ï£¶

ï£·ï£·

ï£¸

â¢

R1=

224k

ï£«

ï£¬ï£¬

ï£

1.1V

VIN(FALLING)

1.1V

ï£¶

ï£·ï£·

ï£¸

â¢

R1â

90.8k

Choose standard values for R2 = 226k and R3 = 91k.

The ISET pin should be left open in this example to select

maximum peak current (50mA). Figure 9 shows a complete

schematic for this design example.

VIN

24V

VIN

LTC3632

220ÂµH

VOUT

3.3V

20mA

1ÂµF

RUN

ISET

10ÂµF

226k

750k

HYST

VFB

91k

GND

240k

3632 F09

3. Keep the switching node, SW, away from all sensi-

tive small-signal nodes. The rapid transitions on the

switching node can couple to high impedance nodes,

in particular VFB, and create increased output ripple.

4. Flood all unused area on all layers with copper. Flooding

with copper will reduce the temperature rise of power

components. You can connect the copper areas to any

DC net (VIN, VOUT, GND or any other DC rail in your

system).

VIN

1 L1

VOUT

LTC3632

5 RUN

VFB 6

CIN

7 HYST

4 SS

ISET 3

COUT

CSS

GND

8, 9

RSET

3632 F10a

VIN

CIN COUT

VOUT

Figure 9. 24V to 3.3V, 20mA Regulator at 250kHz

PC Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of

the LTC3632. Check the following in your layout:

1. Large switched currents flow in the power switches

and input capacitor. The loop formed by these compo-

nents should be as small as possible. A ground plane

is recommended to minimize ground impedance.

2. Connect the (+) terminal of the input capacitor, CIN, as

close as possible to the VIN pin. This capacitor provides

the AC current into the internal power MOSFETs.

RSET CSS

GND

VIAS TO GROUND PLANE

VIAS TO INPUT SUPPLY (VIN)

OUTLINE OF LOCAL GROUND PLANE

3632 F10b

Figure 10. Layout Example

3632fc

▷