ISL6313 Datasheet, PDF (26/33 Pages) Intersil Corporation – Two-Phase Buck PWM Controller with Integrated MOSFET Drivers for Intel VR11 and AMD Applications

ISL6313
PVCC
BOOT
R_HI1
R_LO1
PHASE
UGATE
C_GD
G
R_G1
R_GI1
C_GS
S
D
C_DS
Q₁
FIGURE 18. TYPICAL UPPER-GATE DRIVE TURN-ON PATH
PVCC
R_HI2
R_LO2
LGATE
C_GD
G
R_G2
R_GI2
C_GS
S
D
C_DS
Q₂
FIGURE 19. TYPICAL LOWER-GATE DRIVE TURN-ON PATH
The total gate drive power losses are dissipated among the
resistive components along the transition path and in the
bootstrap diode. The portion of the total power dissipated in
the controller itself is the power dissipated in the upper drive
path resistance, P_{DR_UP}, the lower drive path resistance,
P_{DR_UP}, and in the boot strap diode, P_BOOT. The rest of the
power will be dissipated by the external gate resistors (R_G1
and R_G2) and the internal gate resistors (R_GI1 and R_GI2) of
the MOSFETs. Figures 18 and 19 show the typical upper and
lower gate drives turn-on transition path. The total power
dissipation in the controller itself, P_DR, can be roughly
estimated as:
P_DR = P_{DR_UP} + P_{DR_LOW} + P_BOOT + (I_Q ⋅ VCC)
(EQ. 33)
P_BOOT
=
-^P----^Q----^g----^_--^Q-----¹-
3
P _{D R _UP}
=
⎛
⎜
⎝
-------------^R-----^H----^I--¹--------------
R_HI1 + R_EXT1
+
R^-----_L^---_O^-----₁^{R----+-L---O-}R^----1-_E^----_X^----_T^---₁^- _{⎠⎟⎞}
⋅
P_{-----Q----g----_--Q-----1-}
3
P _{D R _LOW}
=
⎛
⎜
⎝
-------------^R-----^H----^I--²--------------
R_HI2 + R_EXT2
+
R^-----_L^---_O^-----₂^{R----+-L---O-}R^----2-_E^----_X^----_T^---₂^- _{⎠⎟⎞}
⋅ ^P-----^Q----^g----^_---^Q----²-
2
R_EXT1
=
R_G
1
+
R_{-----G-----I-1--}
N_Q1
R_EXT2
=
R_G2
+
R_{-----G-----I-2--}
N_Q2
Inductor DCR Current Sensing Component
Selection
The ISL6313 senses each individual channel’s inductor
current by detecting the voltage across the output inductor
DCR of that channel (As described in the “Continuous Current
Sensing” on page 12). As Figure 20 illustrates, an R-C
network is required to accurately sense the inductor DCR
voltage and convert this information into a current, which is
proportional to the total output current. The time constant of
this R-C network must match the time constant of the inductor
L/DCR.
Follow the steps below to choose the component values for
this RC network.
1. Choose an arbitrary value for C₁. The recommended
value is 0.1μF.
2. Plug the inductor L and DCR component values, and the
value for C₁ chosen in step 1, into Equation 34 to
calculate the value for R₁.
R₁
=
------------^L-------------
DCR ⋅ C₁
(EQ. 34)
Once the R-C network components have been chosen, the
effective internal R_ISEN resistance must then be set. The
R_ISEN resistance sets the gain of the load line regulation
loop as well as the gain of the channel-current balance loop
and the overcurrent trip level. The effective internal R_ISEN
resistance is set through a single resistor on the RSET pin,
R_SET.
MOSFET
DRIVER
UGATE
LGATE
V_IN
IL
L
DCR
V_OUT
INDUCTOR
V_L(s)
C_OUT
V_C(s)
R₁
C₁
ISL6313 INTERNAL CIRCUIT
I_n
SENSE
+
-
I_SEN
V_C(s)
R_ISEN
ISEN-
ISEN+
RSET
R_SET
VCC
FIGURE 20. DCR SENSING CONFIGURATION
Use Equation 35 to calculate the value of R_SET. In
Equation 35, DCR is the DCR of the output inductor at room
temperature, I_OCP is the desired overcurrent trip level, and
26
FN6448.0
March 5, 2007