CS5307GDWR24 datasheet(23/24 Pages) ONSEMI

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CS5307

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Figure 31. At Full−Load the Peak−to−Peak Voltage

Ripple on the COMP Pin Should Be Less than 20 mV

for a Well−Tuned/Stable Controller. Higher COMP

Voltage Ripple Will Contribute to Output Voltage Jitter.

Figure 32. The Value of CAMP Is Optimal. COMP Slews

Quickly Without Spiking or Ringing. VOUT Does Not

Overshoot and Monotonically Settles to Its Final Value.

VOCSET + (IOUT,LIM ) DILo 2) @ R @ GILIM (34)

where:

IOUT,LIM is the current limit threshold of the converter;

ΔILo/2 is half the inductor ripple current;

R is either (RLMAX + RPCB) or RSENSE;

GILIM is the current sense to OCSET gain.

For the overcurrent protection to work properly, the

current sense time constant (RC) should be slightly larger

than the RL time constant. If the RC time constant is too fast,

a step load change will cause the sensed current waveform

to appear larger than the actual inductor current and will trip

the current limit at a lower level than expected.

10. PWM Comparator Input Voltage

The voltage at the positive input terminal of the PWM

comparator (see Figure 14 or 16) is limited by the internal

voltage supply of the controller (3.3 V), the size of the

internal ramp and the magnitude of the channel startup offset

voltage. To prevent the PWM comparator from saturating,

the differential input voltage from CSREF to CSn (n = 1, 2,

3, or 4) must satisfy the following equation:

VCSREF,MAX ) VCOx,MAX ) 600 mV @ D v 2.45 V

(35)

where:

VCSREF,MAX + Max VID Setting w AVP @ Full Load

VCOn,MAX + [VCSx * VCSREF] @ GCSA,MAX

+ (IO,MAX 2 ) DILo 2) @ RMAX

@ GCSA,MAX

RMAX + RSENSE or (RL,MAX ) RPCB,MAX)

11. Soft Start Time

The Soft Start time (TSS) can be calculated from:

+ CSS @

VCOMP * Channel_Startup_Offset

160 mA

(36)

TSS + CSS @ DV

ISS

where:

+ 2.353 Vdc (from page 12)

VCOMP + VOUT @0 A ) Channel_Startup_Offset

) Int_Ramp ) GCSA @ Ext_Ramp 2

If CSS = 0.1 μF, then the Soft Start time will be:

TSS + 0.1 mF @

1.753 Vdc

160 mA +

1.1 ms

(37)

The Channel_Startup_Offset is subtracted from VCOMP

as the output does not begin to rise until VCOMP exceeds this

voltage. As the internal and external ramp values are small,

the Soft Start time may be approximated by:

TSS + CSS @

VOUT @0 A

ISS

(38)

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