PM6652 datasheet(36/53 Pages) STMICROELECTRONICS

36 / 53 page

Device description

PM6652

36/53

Doc ID 16867 Rev 5

If the current sourced by the IMONFB pin is greater than IMAX for more than 4 ms (typ.) the

average current limit fault is detected and the IC latches off: the MOS drivers are put in high

impedance and the internal discharge MOSFET is turned on (see

Figure 37). A COREON

or SVCC toggle is required in order to restart the device.

Every time the IMONFB pin current becomes lower than IMAX, the internal timer is reset (see

Figure 38); as a consequence the inductor current which can cause the average current limit

fault is given by:

Equation 16

In order to set the right average current limit threshold, the PM6652 internal parameters and

also external component accuracy must be considered.

A complete equation for the average current limit threshold worst case variation is:

Equation 17

assuming

δR

G/RG, the accuracy of RG, αIMAX<10%, the internal current reference error,

VIMON,off<1 mV the IMON maximum offset, GSNS the NTC thermal compensation network

attenuation (see

Equation 11),

δR

SNS/RSNS the inductor DCR or precision resistor accuracy

and

δG

SNS/GSNS the thermal compensation network gain error, due to NTC and others

resistors accuracy (see

Equation 25). If the thermal compensation network is not used

and/or the current sensing filter resistor value is higher than the suggested one (as

explained it

Section 8.7: Current sensing) the previous equation must be modified in order to

take into account the DCR thermal drift and current sensing additional offset.

DCR

MAX

AVCL

OUT

AVCL

⋅

≥

∆

−

Figure 37.

Average current limit - recovery

Figure 38.

Average current limit detected

()

⎟⎟⎠

⎞

⎜⎜⎝

⎛ δ

⎟⎟⎠

⎞

⎜⎜⎝

⎛ δ

⎟⎟⎠

⎞

⎜⎜⎝

⎛

⋅

⎟⎟⎠

⎞

⎜⎜⎝

⎛ δ

SNS

AVCL

SNS

off

IMON

IMAX

AVCL

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