ISL6366 Datasheet, PDF (18/44 Pages) Intersil Corporation – Dual 6-Phase + 1-Phase PWM Controller for VR12/IMVP7 Applications

ISL6366
A simple R-C network across the current sense resistor extracts
the R_SEN voltage, as shown in Figure 7.
The voltage on the capacitor V_C, can be shown to be proportional
to the channel current I_L. See Equation 9.
V_C(s) = -^⎝⎛--^s----^â‹-----^R--^E------^S--^S----^E----^L₍--^N----_s---+-_â‹---_R-¹---_C-^⎠⎞----^â‹_+---⁽--_1R----₎-^S---^E---^N-----^â‹---^I--^L---⁾
(EQ. 9)
If the R-C network components are selected such that the RC time
constant matches the ESL-R_SEN time constant (R*C = ESL/R_SEN),
the voltage across the capacitor V_C is equal to the voltage drop
across the R_SEN, i.e., proportional to the channel current. As an
example, a typical 1mΩ sense resistor can use R = 348 and
C = 820pF for the matching. Figures 7 and 8 show the sensed
waveforms without and with matching RC when using resistive
sense.
Because of the internal filter at the ISENS- pin, one capacitor, C_T,
is needed to match the time delay between the ISENS- and
ISENS+ signals. Select the proper C_T to keep the time constant of
R_ISEN and C_T (R_ISEN x C_T) close to 27ns.
FIGURE 7. VOLTAGE ACROSS R WITHOUT RC
The inductor DCR value will increase as the temperature increases.
Therefore, the sensed current will increase as the temperature of
the current sense element increases. In order to compensate the
temperature effect on the sensed current signal, a Negative
Temperature Coefficient (NTC) resistor can be used for thermal
compensation, or the integrated temperature compensation
function of ISL6366 should be utilized. The integrated temperature
compensation function is described in “Temperature
Compensation” on page 30.
Decoupling capacitor (C_T) on ISEN[6:1]- pins are optional and
might be required for long sense traces and a poor layout.
IL(s)
L
DCR
INDUCTOR
V_L
V_OUT
C_OUT
ISL6366
I_n
V_C(s)
R
C
CURRENT
SENSE
+
R_ISEN(n)
-
I_SEN
=
I_L
D_-----C_----R_-----⋅_---6_----4_--
R_SET
ISEN-(n)
ISEN+(n)
RSET
C_T, Optional
FIGURE 8. VOLTAGE ACROSS C WITH MATCHING RC
Equation 10 shows that the ratio of the channel current to the
sensed current, I_SEN, is driven by the value of the sense resistor
and the R_ISEN.
I_SEN
=
I_L
⋅
-^R-----^S---^E---^N---
R_ISEN
(EQ. 10)
Figures 5 and 6 configurations apply for VR1 output, while the
R_ISEN should include the internal metal impedance of 10.5Ω for
accurate current sense.
For VR0 output, the R_ISEN resistor of each channel is integrated,
while its value is determined by the R_SET resistor. The RSET resistor
value can be from 3.84kΩ to 115.2kΩ and is 64x of the required
I_SEN resistor value. Therefore, the current sense gain resistor
(Integrated R_ISEN) value can be effectively set at 60Ω to 1.8kΩ.
Figures 9 and 10 show the configurations for inductor DCR sensing
and resistive sensing of VR0, respectively; their sensing current is
represented by Equations 11 and 12, respectively.
I_SEN
=
I_L
⋅
D_-----C_----R_-----⋅_---6_----4_--
R_SET
(EQ. 11)
I_SEN
=
I_L
⋅
R_{-----S---E---N-----}⋅_---6_----4_--
R_SET
(EQ. 12)
FIGURE 9. DCR SENSING CONFIGURATION FOR VR0
ISL6366
I_n
L
R
IL
R_SEN ESL
R_SENSE
V_R
V_C(s)
C
V_OUT
C_OUT
CURRENT
SENSE
+
R_ISEN(n)
-
I_SEN
=
I_L
R_{-----S---E---N-----}⋅_---6_----4_--
R_SET
ISEN-(n)
ISEN+(n)
RSET
C_T, Optional
FIGURE 10. SENSE RESISTOR IN SERIES WITH INDUCTORS FOR
VR0
18
FN6964.0
January 3, 2011