8

current, the signal applied via the summing Correction circuit

to the Comparator, reduces the output pulse width of the

Comparator to compensate for the detected “above average”

current in that channel.

Droop Compensation

In addition to control of each power channel’s output current,

the average channel current is also used to provide CORE

voltage “droop” compensation. Average full channel current

is defined as 50

amount of voltage droop required at full load current can be

programmed. The average current driven into the FB pin

direction to make the Error Amplifier “see” a higher voltage at

the inverting input, resulting in the Error Amplifier adjusting

is equal to the “droop” voltage. See the “Current Sensing and

Balancing” section for more details.

Applications and Convertor Start-Up

Each PWM power channel’s current is regulated. This

enables the PWM channels to accurately share the load

current for enhanced reliability. The HIP6601, HIP6602 or

HIP6603 MOSFET driver interfaces with the HIP6311A. For

more information, see the HIP6601, HIP6602 or HIP6603

data sheets.

The HIP6311A is capable of controlling up to 4 PWM power

automatically sets the number of channels. The phase

PWM channels. For example, for three channel operation,

PWM output signals for a four channel system.

Power supply ripple frequency is determined by the channel

For example, if the channel frequency is set to 250kHz and

there are three phases, the ripple frequency is 750kHz.

The IC monitors and precisely regulates the CORE voltage

of a microprocessor. After initial start-up, the controller also

provides protection for the load and the power supply. The

following section discusses these features.

Initialization

The HIP6311A usually operates from an ATX power supply.

Many functions are initiated by the rising supply voltage to the

Start and other functions are initialized during this interval.

These circuits are controlled by POR, Power-On Reset. During

this interval, the PWM outputs are driven to a three state

condition that makes these outputs essentially open. This state

results in no gate drive to the output MOSFETs.

level to insure proper internal function, the PWM outputs are

enabled and the Soft-Start sequence is initiated. If for any

POR circuit shuts the converter down and again three states

the PWM outputs.

Soft-Start

4.375V, the Soft-Start sequence is initiated. Soft-Start, by its

slow rise in CORE voltage from zero, avoids an over-current

condition by slowly charging the discharged output

capacitors. This voltage rise is initiated by an internal DAC

that slowly raises the reference voltage to the error amplifier

input. The voltage rise is controlled by the oscillator

frequency and the DAC within the HIP6311A, therefore, the

output voltage is effectively regulated as it rises to the final

programmed CORE voltage value.

For the first 32 PWM switching cycles, the DAC output

remains inhibited and the PWM outputs remain three stated.

From the 33rd cycle and for another, approximately 150 cycles

the PWM output remains low, clamping the lower output

MOSFETs to ground, see Figure 3. The time variability is due

to the Error Amplifier, Sawtooth Generator and Comparators

moving into their active regions. After this short interval, the

PWM outputs are enabled and increment the PWM pulse

width from zero duty cycle to operational pulse width, thus

allowing the output voltage to slowly reach the CORE voltage.

The CORE voltage will reach its programmed value before the

2048 cycles, but the PGOOD output will not be initiated until

the 2048th PWM switching cycle.

160

µs, the PWM outputs are held in a three state level as

explained above. After this period and a short interval

described above, the PWM outputs are initiated and the

voltage rises in 10.08ms, for a total delay time DT of

10.24ms.

PWM 1

PWM 2

PWM 3

PWM 4

FIGURE 2. FOUR PHASE PWM OUTPUT AT 500kHz

HIP6311A

HIP6311A