MIC2593 datasheet(25/26 Pages) STMICROELECTRONICS

25 / 26 page

April 2004

M9999-042204

MIC2593

Micrel

Gate Capacitor and Resistor Guidelines

The MIC2593 controls four external power MOSFETs, that

handle the high currents for each of the two 3.3V and 5V

outputs. A capacitor is connected in the application circuit

from each GATE pin of the MIC2593 to ground. However, an

external capacitor, C

GATE, is not required for operation of the

MIC2593. Each C

GATE controls the ramp-up rate of its

respective power output (e.g., 5VOUTB). These capacitors,

which are typically in the 10nF range, cause the GATE

outputs of the MIC2593 to have very low AC impedances to

ground at any significant frequency. It is therefore necessary

to place a modest value of gate damping resistance (R

GATE)

between each C

GATE and the gate of its associated MOSFET

as shown in Figure 15. These resistances prevent high-

frequency MOSFET source-follower oscillations from occur-

ring. The exact value of the resistors used is not critical; 10

Ω

to 33

Ω is usually a sufficient choice. Each R

GATE should be

physically located directly adjacent to the MOSFET gate lead

to which it connects.

MIC2593

GATE

RGATE

Ω

CGATE

10nF

External

MOSFET

Figure 15. C

GATE and RGATE Connection

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