IPM6220A

FN9032 Rev 1.00

Page 10 of 14

Aug 2004

operating open circuit and the output voltage varies with the

output load resistance, Ro, as given by:

Where Vin is the 5V Main voltage, Dmax = 0.33, L is the value

of the boost inductor, L3, and F = 100kHz. This provides

automatic output current limiting. When the maximum duty

cycle has been reached and for a given inductor, a further

reduction in Ro by one-half will pull the output voltage down to

0.707 of nominal and cause an undervoltage condition.

The 12V converter starts to operate at the same time as the 5V

Main converter. The rising voltage on the 5V Main output and

the 33% duty cycle limit provides a similar soft-start, as the 5V

Main, for the 12V output.

3V ALWAYS, 5V ALWAYS Linear Regulators

The 3.3V ALWAYS and 5V ALWAYS outputs are derived from

the battery voltage and are the first voltages available in the

notebook when power on is initiated. The 5V ALWAYS output

is generated directly from the battery voltage by a linear

regulator. It is used to power the system micro- controller and

to internally power the chip and the gate drivers. The 3.3V

ALWAYS output is generated from the 5V ALWAYS output and

may be used to power the keyboard controller or other

peripherals. The combined current capability of these outputs

is 50mA. When the 5V Main output is greater than it’s

undervoltage level, it is switched to the 5V ALWAYS output via

an internal 1.3

ALWAYS linear regulator is disabled to prevent excessive

power dissipation.

The rise time of the 5V ALWAYS is determined by the value of

the output capacitance on the 5V and 3.3V ALWAYS outputs.

The internal regulator is current limited to about 180mA, so the

startup time is approximately:

3.3V ALWAYS outputs.

Power Good Status

The IPM6220A monitors all the output voltages except for the

3.3V ALWAYS. A single power-good signal, PGOOD, is issued

when soft-start is completed and all monitored outputs are

within 10% of their respective set points. After the soft-start

sequence is completed, undervoltage protection latches the

chip off when any of the monitored outputs drop below 75% of

its set point.

A ‘soft-crowbar’ function is implemented for an overvoltage on

the 3.3V Main or 5V Main outputs. If the output voltage goes

above 115% of their nominal output level, the upper MOSFET

is turned off and the lower MOSFET is turned on. This ‘soft-

crowbar’ condition will be maintained until the output voltage

returns to the regulation window and then normal operation will

continue.

This ‘soft-crowbar’ and monitoring of the output, prevents the

output voltage from ringing negative as the inductor current

flows in the ‘reverse’ direction through the lower MOSFET and

output capacitors.

Over-Temperature Protection

The IC incorporates an over-temperature protection circuit that

shuts all the outputs down when the die temperature exceeds

150°C. Normal operation is automatically restored when the

die temperature cools to 125°C.

Component Selection Guidelines

Output Capacitor Selection

The output capacitors for each output have unique

requirements. In general, the output capacitors should be

selected to meet the dynamic regulation requirements

including ripple voltage and load transients.

3.3V Main and 5V Main PWM Output Capacitors

Selection of the output capacitors is also dependent on the

output inductor so some inductor analysis is required to select

the output capacitors.

One of the parameters limiting the converter’s response to a

load transient is the time required for the inductor current to

slew to its new level. Given a sufficiently fast control loop

design, the IPM6220A will provide either 0% or 94% duty cycle

in response to a load transient. The response time is the time

interval required to slew the inductor current from an initial

current value to the load current level. During this interval the

difference between the inductor current and the transient

current level must be supplied by the output capacitor(s).

Minimizing the response time can minimize the output

capacitance required. Also, if the load transient rise time is

slower than the inductor response time, as in a hard drive or

CD drive, this reduces the requirement on the output capacitor.

The maximum capacitor value required to provide the full,

rising step, transient load current during the response time of

the inductor is:

drop in output voltage allowed during the load transient.

High frequency capacitors initially supply the transient current

and slow the load rate-of-change seen by the bulk capacitors.

The bulk filter capacitor values are generally determined by the

ESR (Equivalent Series Resistance) and voltage rating

requirements as well as actual capacitance requirements. The

Vo

Vin Dmax



Ro

2LxF



-------------------





=

5V

180mA

-------------------



=



–

 2



----------------------------------------------

--------------------



=