Micrel
MICRF009
CAGC = AGC capacitor value
∆t = droop recovery time
∆V = droop voltage
For example, if user desires ∆t = 10ms and chooses a
4.7µF CAGC, then the allowable droop is about 144mV.
Using the same equation with 200nA, the worst-case pin
leakage, and assuming 1µA of capacitor leakage in the
same direction, the maximum allowable ∆t (shutdown time)
is about 0.56s for droop recovery in 10ms.
The ratio of decay-to-attack time-constant is fixed at 1:10
(that is, the attack time constant is 10 times of the decay
time constant). Generally the design value of 1:10 is
adequate for the vast majority of applications. If adjustment
is required, adding a resistor in parallel of the CAGC
capacitor may vary the ratio. The value of the resistor must
be determined on a case-by-case basis.
January 18, 2005
9
M9999-011805
(408) 955-1690