ISL6263C Datasheet, PDF (15/18 Pages) Intersil Corporation – 5-Bit VID Single-Phase Voltage Regulator with Current Monitor for GPU Core Power

ISL6263C
VDD
−
OCP
+
+
−
10µA _↓
OCSET
+
I_SENSE
−
ISP
ISN
ICOMP
VO
R_OCSET
R_S
+
V_N ^RP
- ^(OPTIONAL)
V_RSNS
FIGURE 9. EQUIVALENT MODEL OF CURRENT SENSE USING DISCRETE RESISTOR CURRENT SENSE
0.00393 is the temperature coefficient of the copper. To
make V_ICOMP independent of the inductor temperature, the
NTC characteristic is desired to satisfy:
G₁(T) ⋅ (1 + 0.00393 ⋅ T – (+25°C)) ≅ G_{1t arget}
(EQ. 16)
where G_1target is the desired ratio of V_N / V_DCR. Therefore,
the temperature characteristics G₁, which determines
parameters selection, is described by Equation 17:
G₁(T)
=
--------------------------^G-----¹---^t--^a---^r--^g---^e----^t-------------------------
1 + 0.00393 ⋅ (T – (+25°C))
(EQ. 17)
It is recommended to begin the DCR current sense design
using the R_NTC, R_NTCS, and R_P component values of the
evaluation board available from Intersil.
Given the inductor DCR and the overcurrent set point I_OC, the
maximum voltage of ICOMP pin is determined by
Equation 18:
V_ICOMP(max) – V_O
=
I_OC
⋅
DC
R
( 25
°
C
)
⋅
-_R----_N---^R-₍---₊^N----₂-⁽--⁺⁵----_°²---_C5----^°-₎--^C-+----⁾-_R----_S--
⋅
⎛
⎜
⎝
1
+
RR_{-----II--SS----21-⎠⎟⎞}
(EQ. 18)
R_N, R_S, R_IS1, R_IS2 should be adjusted to meet the
requirement (V_ICOMP(max) - V_O) > 25mV and the time
constant matching according to Equation 10.
The effectiveness of the R_N network is sensitive to the
coupling coefficient between the NTC thermistor and the
inductor. The NTC thermistor should be placed in the closet
proximity of the inductor.
Resistor Current Sense
Figure 3 shows a detailed schematic using discrete resistor
sense of the inductor current. Figure 9 shows the equivalent
circuit. Since the current sense resistor voltage represents
the actual inductor current information, R_S and C_N simply
provide noise filtering. A low ESL sense resistor is strongly
recommended for R_SNS because this parameter is the most
significant source of noise that affects discrete resistor
sense. It is recommended to start out using 100Ω for R_S and
47pF for C_N. Since the current sense resistance changes
very little with temperature, the NTC network is not needed
for thermal compensation. Discrete resistor sense design
follows the same approach as DCR sense. The voltage on
the current sense resistor is given by Equation 19:
V_RSNS = I_O ⋅ R_SNS
(EQ. 19)
It is optional to parallel a resistor R_P to form a voltage divider
with R_S to obtain more flexibility. Assume the voltage across
R_P is V_N, which is given by Equation 20:
V_N
=
V_RSNS
⋅
--------^R----^P---------
R_S + R_P
(EQ. 20)
The current sense amplifier output voltage V_ICOMP is given
by Equation 21:
V_ICOMP
=
V_O
+
V_N
⋅
⎛
⎜1
⎝
+
R^{-R----II--SS----21-}_{⎠⎟⎞}
(EQ. 21)
Given an current sense resistor R_SNS and the overcurrent set
point I_OC, the maximum voltage of ICOMP pin is determined
by Equation 22:
V_ICOMP(max) – V_O
=
I_O
C
⋅
R_S
N
S
⋅
--------^R----^P---------
R_S + R_P
⋅
⎛
⎜
⎝
1
+
R^{-R----II--SS----21-}_{⎠⎟⎞}
(EQ. 22)
If R_P is not used, the maximum voltage of ICOMP pin is
determined by Equation 23:
V_ICOMP(max) – V_O
=
I_O
C
⋅
R_SN
S
⋅
⎛
⎜1
⎝
+
RR_{-----II--SS----21-⎠⎟⎞}
(EQ. 23)
R_S, R_P, R_IS1, R_IS2 should be adjusted to meet the
requirement (V_ICOMP(max) - V_O) > 25mV.
The current sense traces should be routed directly to the
current sense resistor pads for accurate measurement.
However, due to layout imperfection, the calculated R_IS2
may still need slight adjustment to achieve optimum load line
slope. It is recommended to adjust R_IS2 after the system has
achieved thermal equilibrium at full load.
15
FN6745.1
July 8, 2010