MIC22200YML datasheet(13/22 Pages) MICREL

13 / 22 page

Micrel, Inc.

MIC22200

December 2010

M9999-120310-C

DELAY Pin

The DELAY pin also has a 1µA trimmed current source

and a 1µA current sink which acts with an external

capacitor to delay the operation of the POR output. This

can be used also in sequencing outputs in a sequenced

system, but with the addition of a conditional delay

between supplies; allowing a first up, last down power

sequence.

After EN/DLY pin is driven high, VOUT will start to rise

(rate determined by RC capacitor). As the FB voltage

goes above 90% of its nominal set voltage, DELAY pin

begins to rise as the 1µA source charges the external

capacitor. When the threshold of 1.24V is crossed, POR

is asserted high and DELAY pin continues to charge to a

voltage VDD. When FB falls below 90% of nominal, POR

is asserted low immediately. However, if EN/DLY pin is

driven low, POR will fall immediately to the low state and

DELAY pin will begin to fall as the external capacitor is

discharged by the 1µA current sink. When the threshold

of VDD -1.24V is crossed, VOUT will begin to fall at a rate

determined by the RC capacitor. As the voltage change

in both cases is 1.24V, both rising and falling delays are

matched at

1.10

1.24

DELAY

POR

−

RC Pin

The RC pin provides a trimmed 1µA current source/sink

similar to the DELAY pin for accurate ramp up (soft start)

and ramp down control. This allows the MIC22200 to be

used in systems requiring voltage tracking or ratio-metric

voltage tracking at startup.

There are two ways of using the RC pin:

•

Externally driven from a voltage source

•

Externally attached capacitor sets output ramp

up/down rate

In the first case, driving RC with a voltage from 0V to

VREF will program the output voltage between 0 and

100% of the nominal set voltage.

In the second case, the external capacitor sets the ramp

up and ramp down time of the output voltage. The time

is given by

1.10

0.7

RAMP

−

where TRAMP is the time

from 0 to 100% nominal output voltage.

Sequencing and Tracking Examples

There are four distinct variations which are easily

implemented using the MIC22200. The two sequencing

variations are Windowed and Delayed. The two tracking

variants are Normal and Ratio Metric. Figures 5 thru 10

illustrate methods for connecting two MIC22200’s to

achieve these requirements.

Sequencing

Figure 4. Sequencing MIC22200 Circuit

Figure 5. Window Sequencing Example

Figure 6. Delayed Sequencing Example

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