9

Current Sensing and Balancing

Overview

The HIP6304 samples the on-state voltage drop across each

synchronous rectifier FET, Q2, as an indication of the

inductor current in that phase, see Figure 7. Neglecting AC

effects (to be discussed later), the voltage drop across Q2 is

The voltage at Q2’s drain, the PHASE node, is applied to the

ISEN pin. This pin is held at virtual ground, so the current

following functions:

1. Detection of an over-current condition

2. Reduce the regulator output voltage with increasing load

current (droop)

with the current detected in the other channel. The averaged

current is compared with a trimmed, internally generated

current, and used to detect an over-current condition.

50

µA at full output load current, and the nominal trip point for

over-current detection is 165% of that value, or 82.5

µA.

4m

The over-current trip point would be 165% of 25A, or ~ 41A

over-current trip point, but it is suggested to stay within

±25%

of nominal.

resistors is also steered to the FB pin. There is no DC return

the FB pin. This is the desired “droop” voltage used to maintain

With a high dv/dt load transient, typical of high performance

microprocessors, the largest deviations in output voltage

occur at the leading and trailing edges of the load transient. In

order to fully utilize the output-voltage tolerance range, the

output voltage is positioned in the upper half of the range

when the output is unloaded and in the lower half of the range

when the controller is under full load. This droop

compensation allows larger transient voltage deviations and

thus reduces the size and cost of the output filter components.

FIGURE 7. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING

CURRENT

SENSING

COMPARATOR

PWM

CIRCUIT

AVERAGING

CURRENT

FROM

OTHER

CHANNEL

SAWTOOTH

GENERATOR

+

DIFFERENCE

+

CORRECTION

ERROR

AMPLIFIER

FB

COMP

REFERENCE

TO OTHER

CHANNEL

Q1

Q2

COMPARATOR

REFERENCE

TO OVER

CURRENT

TRIP

PHASE

INDUCTOR

CURRENT

FROM

OTHER

CHANNEL

PWM

DAC

HIP6304

ONLY ONE OUTPUT

HIP6601

-

-

STAGE SHOWN

-

+

SENSING

-

+

-

+

HIP6304