ISL6567 Datasheet, PDF (13/26 Pages) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

ISL6567
SETTING THE OUTPUT VOLTAGE
The ISL6567 uses a precision internal reference voltage to
set the output voltage. Based on this internal reference, the
output voltage can thus be set from 0.6V up to a level
determined by the input voltage, the maximum duty cycle,
and the conversion efficiency of the circuit; Equation 7
estimates this maximum amplitude the output voltage can be
regulated to. Obviously, insure that the input voltage and all
the voltages sampled by the ISL6567 do not exceed the
controller’s absolute maximum limits, or any other limits
specified in this document.
V_REF
ISL6567
+
ERROR ^-
AMPLIFIER
EXTERNAL CIRCUIT
FB
R₁
VDIFF
+
X1
-
DIFFERENTIAL
AMPLIFIER
VSEN
RGND
R_S
+
R_P
To V_OUT
-
FIGURE 8. SETTING THE OUTPUT VOLTAGE AT THE INPUT
OF THE DIFFERENTIAL AMPLIFIER
V_OUTMAX = d_MAX ⋅ V_IN ⋅ Efficiency
(EQ. 7)
ISL6567
V_REF
+
ERROR ^-
AMPLIFIER
EXTERNAL CIRCUIT
FB
R_S(R₁)
+
To V_OUT
R_P
VDIFF
+
X1
-
DIFFERENTIAL
AMPLIFIER
VSEN
RGND
FIGURE 9. SETTING THE OUTPUT VOLTAGE AT THE FB PIN
The differential amplifier can be used even if remote output
sensing is not desired or not feasible, simply connect RGND
to the local ground and connect VSEN to the output voltage
being monitored. Should one desire to bypass the differential
amplifier, the circuit in Figure 9 is recommended as the
proper implementation. Since its output is monitored for OVP
and PGOOD purposes, the differential amplifier needs to be
connected to the feedback circuit at all times, hence its input
connections to FB and local ground. However, its output,
VDIFF, can be left open. The resistor divider setting the
output voltage is calculated in a manner identical to that
already revealed.
ISL6567
EXTERNAL
CIRCUIT
The output voltage can be set via a simple resistor divider,
as shown in Figure 8. It is recommended this resistor divider
is connected at the input of the differential amplifier (as this
amplifier is powered from the IC’s 5V bias and has limited
input range). To avoid degradation of DC regulation
tolerance due to the differential amplifier’s input resistance, a
size requirement is placed on the combined value of R_P and
R_S. Consider R to be the parallel combination of these two
resistors, and use a value of 2kΩ or less for R; use the
following equations to determine the value of R_P and R_S,
based on the desired output voltage, the reference voltage,
and the chosen value of R.
R_P
=
R
⋅
-----------^V-----^O----^U----^T-------------
V_OUT – V_REF
R_S
=
R
⋅
V_{-----O----U----T--}
V_REF
(EQ. 8)
-
+
DIFFERENTIAL
AMPLIFIER
Z_IN
~2µA
VDIFF
VSEN
RGND
Z_IN > 240kΩ
OVER PROCESS, TEMPERATURE, AND
0 < VSEN-RGND < 2.5V
FIGURE 10. SETTING THE OUTPUT VOLTAGE AT THE INPUT
OF THE DIFFERENTIAL AMPLIFIER
13
FN9243.3
May 28, 2009