ISL62871 Datasheet, PDF (12/25 Pages) Intersil Corporation – PWM DC/DC Controller With VID Inputs For Portable GPU Core-Voltage Regulator

ISL62871, ISL62872
The ISL62872 V_SET1 setpoint is written as Equation 9:
V_SET1 = V_REF
(EQ. 9)
The ISL62872 V_SET2 setpoint is written as Equation 10:
V_SET2
=
V_REF
⋅
⎛
⎜1
⎝
+
R^-----_S^----_E^----_T^----₂^----+-----RR^{----SS----EE----TT----13----+-----}R^-----_S^----_E^---_T^----₄^- _{⎠⎟⎞}
(EQ. 10)
The ISL62872 V_SET3 setpoint is written as Equation 11:
V_SET3
=
V_REF
⋅
⎛
⎜1
⎝
+
RR_{-----SS----EE----TT----13----++-----}RR_{----SS----EE----TT----24-⎠⎟⎞}
(EQ. 11)
The ISL62872 V_SET4 setpoint is written as Equation 12:
V_SET4
=
V_REF
⋅
⎛
⎜1
⎝
+
R_{-----S----E----T----1----+-----RR----SS----EE----TT----24----+-----}R_{-----S----E---T----3- ⎠⎟⎞}
(EQ. 12)
V_OUT R_FB
FB
SREF
SET0
−
EA
+
V_COMP
+
V_SET
−
V_REF
500mV
SW0
SW1
The equation for the value of R_SET1 is written as
Equation 13:
R_SET1
=
R_SET2
⋅
⎛
⎜
⎝
K_-----V_{----S----E----T----2-}
V_REF
–
⎞
1⎟
⎠
(EQ. 13)
The sum of R_SET1 and R_SET2 programming resistors should
be approximately 300kΩ as shown in Equation 14 otherwise
adjust the value of R_SET2 and repeat the calculations.
R_SET1 + R_SET2 ≅ 300kΩ
(EQ. 14)
Equations 15 and 16 give the specific V_SET gain equations
for the ISL62871 setpoint reference voltages.
The ISL62871 V_SET1 setpoint is written as Equation 15:
V_SET1 = V_REF
(EQ. 15)
The ISL62871 V_SET2 setpoint is written as Equation 16:
V_SET2
=
V_R
E
F
⋅
⎛
⎜
⎝
1
+
R^{-R----SS----EE----TT----12-}_{⎠⎟⎞}
(EQ. 16)
V_OUT R_FB
FB
SREF
−
EA
+
V_COMP
+
V_SET
−
V_REF
SW0
SET1
SW2
SET0
SW1
SET2
SW3
FIGURE 9. ISL62871 VOLTAGE PROGRAMMING CIRCUIT
FIGURE 8. ISL62872 VOLTAGE PROGRAMMING CIRCUIT
Component Selection for ISL62871 Setpoint
Voltage Programming Resistors
TABLE 2. ISL62871 VID TRUTH TABLE
STATE
RESULT
VID0
CLOSE
V_SREF
V_OUT
1
SW0
V_SET1
V_OUT1
0
SW1
V_SET2
V_OUT2
First, determine the attenuation factor K. Next, assign an
initial value to R_SET2 of approximately 150kΩ then calculate
R_SET1 using Equation 13.
12
FN6707.0
August 14, 2008