HIP6301VCB datasheet(13/20 Pages) RENESAS

13 / 20 page

HIP6301V, HIP6302V

FN9034 Rev 3.00

Page 13 of 20

May 5, 2008

Current Sensing and Balancing

Overview

The HIP6301V and HIP6302V sample the on-state voltage

drop across each synchronous MOSFET, Q2, as an

indication of the inductor current in that phase, see Figure 9.

Neglecting AC effects (to be discussed later), the voltage

drop across Q2 is simply rDS(ON)(Q2) x inductor current (IL).

Note that IL, the inductor current, is either 1/2, 1/3, or 1/4 of

the total current (ILT), depending on how many phases are

in use.

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

RISEN resistor to develop the IISEN current through the ISEN

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

RISEN is shown in Equation 1:

The IISEN current provides information to perform the

following functions:

1. Detection of an overcurrent condition

2. Reduce the regulator output voltage with increasing load

current (droop)

3. Balance the IL currents in multiple channels

Overcurrent, Selecting RISEN

The current detected through the RISEN resistor is averaged

with the current(s) detected in the other 1, 2, or 3 channels.

The averaged current is compared with a trimmed, internally

generated current, and used to detect an overcurrent

condition.

The nominal current through the RISEN resistor should be

50µA at full output load current, and the nominal trip point for

overcurrent detection is 165% of that value, or 82.5µA

(typical current levels) as shown in Equation 2. Therefore:

For a full load of 25A per phase, and an rDS(ON) (Q2) of

, RISEN = 2k.

The overcurrent trip point would be 165% of 25A, or ~ 41A

per phase. The RISEN value can be adjusted to change the

overcurrent trip point, but it is suggested to stay within ±25%

of nominal.

FIGURE 9. SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM SHOWING CURRENT AND VOLTAGE SAMPLING

CURRENT

SENSING

COMPARATOR

PWM

CIRCUIT

AVERAGING

CURRENT

FROM

OTHER

CHANNELS

SAWTOOTH

GENERATOR

DIFFERENCE

RISEN

CORRECTION

ERROR

AMPLIFIER

COMP

REFERENCE

TO OTHER

CHANNELS

ISEN

RIN

RFB

VCORE

COMPARATOR

REFERENCE

OVERCURRENT

TRIP

L01

PHASE

INDUCTOR

CURRENT(S)

FROM

OTHER

CHANNELS

PWM

DAC

HIP6301V

VIN

ONLY ONE OUTPUT

HIP6601

STAGE SHOWN

SENSING

(EQ. 1)

rDS ON



ISEN

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



IRISEN

r

DS ON

 Q2



A

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

(EQ. 2)

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