L6738 datasheet(24/32 Pages) STMICROELECTRONICS

24 / 32 page

Application details

L6738

24/32

Doc ID 18133 Rev 1

Set the gain RF/RFB in order to obtain the desired closed loop regulator bandwidth

according to the approximated formula (suggested values for RFB are in the range

of some k

Ω):

Place FZ1 below FLC (typically 0.5*FLC):

Place FP1 at FESR:

Place FZ2 at FLC and FP2 at half of the switching frequency:

Check that compensation network gain is lower than open loop EA gain before

F0dB

Check phase margin obtained (it should be greater than 45°) and repeat if

necessary.

9.2

Layout guidelines

The L6738 provides control functions and high current integrated driver to implement high-

current step-down DC-DC converters. In this kind of application, a good layout is very

important.

The first priority when placing components for these applications has to be reserved to the

power section, minimizing the length of each connection and loop as much as possible. To

minimize noise and voltage spikes (EMI and losses) power connections (highlighted in

Figure 11) must be a part of a power plane and realized by wide and thick copper traces:

loop must be minimized. The critical components, i.e. the power MOSFETs, must be close

to one another. The use of a multi-layer printed circuit board is recommended.

The input capacitance (CIN), or at least a portion of the total capacitance needed, has to be

placed close to the power section in order to eliminate the stray inductance generated by the

copper traces. Low ESR and ESL capacitors are preferred, MLCCs are recommended to be

connected near the HS drain.

Use a proper number of VIAs when power traces have to move between different planes on

the PCB in order to reduce both parasitic resistance and inductance. Moreover, reproducing

the same high-current trace on more than one PCB layer reduces the parasitic resistance

associated to that connection.

----------

0dB

------------

∆V

OSC

-------------------

⋅

π R

⋅⋅

-----------------------------------

π R

ESR

–

⋅⋅

⋅

-------------------------------------------------------------------

⋅

-------------------- 1

–

------------------------------

π R

⋅⋅

-------------------------------------

L6738 Datenblatt(PDF) 24 Page - STMicroelectronics

L6738 Datenblatt(HTML) 24 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datenblatt Download

Link URL