L6701 datasheet(39/44 Pages) STMICROELECTRONICS

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L6701

16 Layout Guidelines

39/44

16.2

Small Signal Components and Connections

These are small signal components and connections to critical nodes of the application as well

as bypass capacitors for the device supply (See Figure 20). Locate the bypass capacitor (VCC

and Bootstrap capacitor) close to the device and refer sensible components such as frequency

set-up resistor ROSC to SGND. Star grounding is suggested: connect SGND to PGND plane in

a single point to avoid that drops due to the high current delivered causes errors in the device

behavior.

VSEN pin filtered vs. SGND helps in reducing noise injection into device: take care in routing

driving net for this pin in order to minimize coupled noise.

Remote Buffer Connection must be routed as parallel nets from the FBG/FBR pins to the load

in order to avoid the pick-up of any common mode noise. Connecting these pins in points far

from the load will cause a non-optimum load regulation, increasing output tolerance.

Locate current reading components close to the device. It's also important to minimize any

offset in the measurement and, to get a better precision, to connect the traces as close as

possible to the sensing elements.

Caution:

Boot Capacitor Extra Charge. Systems that do not use Schottky diodes might show big

negative spikes on the phase pin. This spike can be limited as well as the positive spike but has

an additional consequence: it causes the bootstrap capacitor to be over-charged. This extra-

charge can cause, in the worst case condition of maximum input voltage and during particular

transients, that boot-to-phase voltage overcomes the abs. max. ratings also causing device

failures. It is then suggested in this cases to limit this extra-charge by:

–

adding a small resistor in series to the boot diode (one resistor can be enough for all

the three diodes if placed upstream the boot diode anode, see Figure 20)

–

using non-capacitive boot diodes (such as standard diodes).

Figure 20. Power connections and related connections layout (same for all phases).

CIN

VIN

UGATEx

PHASEx

LGATEx

PGNDx

LOAD

BOOTx

PHASEx

VCC

SGND

+Vcc

CIN

VIN

LOAD

To limit C

BOOT

Extra-Charge

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