ISL62872HRUZ-T Intersil, ISL62872HRUZ-T Datasheet - Page 11

• Manufacturer Part Number: ISL62872HRUZ-T
• Description: IC CTRLR DC/DC PWM 20-TQFN
• Manufacturer: Intersil

Specifications of ISL62872HRUZ-T

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 330kHz
• Duty Cycle: 100%
• Voltage - Supply: 3.3 V ~ 25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -10°C ~ 100°C
• Package / Case: 16-UTQFN (16-µTQFN)
• Frequency-max: 330kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

V
reference voltage where:
The V
corresponds to the closure of internal switch SW0 that
configures the V
follower for the 500mV voltage reference V
A feedback voltage-divider network may be required to
achieve the desired reference voltages. Using the feedback
voltage-divider allows the maximum output voltage of the
converter to be higher than the 1.5V maximum setpoint
reference voltage that can be programmed on the SREF pin.
Likewise, the feedback voltage-divider allows the minimum
output voltage of the converter to be higher than the fixed
500mV setpoint reference voltage of V
voltage-divider network such that the voltage V
voltage V
desired level. The voltage-divider relation is given in
Equation 1:
Where:
The attenuation of the feedback voltage divider is written as:
Where:
Since the voltage-divider network is in the feedback path, all
output voltage setpoints will be attenuated by K, so it follows
that all of the setpoint reference voltages will be attenuated
by K. It will be necessary then to include the attenuation
factor K in all the calculations for selecting the R
programming resistors.
The value of offset resistor R
after the value of loop-compensation resistor R
determined. The Calculation of R
Equation 3:
R
V
K
SET(x)
OFS
FB
- V
- V
- V
- R
- R
- K is the attenuation factor
- V
- V
=
connects from the FB pin to the converter output
connects from the FB pin to the GND pin
500mV or 1.50V
V
V
------------------------------ -
=
V
SET1
OUT1
SET1
FB
SREF lim
SREF(lim)
OUT(lim)
SREF
FB
OFS
=
OUT lim
V
where (x) is the first, second, third, or fourth setpoint
OUT
------------------------------------------- -
V
SREF
= V
is the loop-compensation feedback resistor that
V
OUT
(
is the voltage-scaling programming resistor that
SET x ( )
(
setpoint is fixed at 500mV because it
< V
< V
= V
SREF
⋅
--------------------------------- -
R
)
–
)
is the output voltage of the converter when
when the converter output voltage is at the
SET2
OUT2
SREF(lim)
FB
is the V
V
SET
=
R
SET x ( )
⋅
+
--------------------------------- -
R
OFS
R
FB
R
FB
amplifier as a unity-gain voltage
< V
R
< V
OFS
+
OFS
SREF
R
SET3
OUT3
OFS
OFS
11
voltage setpoint of either
< V
< V
OFS
can be calculated only
OUT4
SET4
is written as
SET1
REF
. Scale the
FB
.
FB
SET
equals the
has been
ISL62871, ISL62872
(EQ. 1)
(EQ. 2)
(EQ. 3)
The setpoint reference voltages are programmed with
resistors that use the naming convention R
is the first, second, third, or fourth programming resistor
connected in series starting at the SREF pin and ending at
the GND pin. When one of the internal switches closes, it
connects the inverting input of the V
specific node among the string of R
resistors. All the resistors between that node and the SREF
pin serve as the feedback impedance R
amplifier. Likewise, all the resistors between that node and
the GND pin serve as the input impedance R
amplifier. Equation 4 gives the general form of the gain
equation for the V
Where:
Calculating Setpoint Voltage Programming
Resistor Values for ISL62872
First, determine the attenuation factor K. Next, assign an
initial value to R
R
respectively. The equation for the value of R
as Equation 5:
The equation for the value of R
The equation for the value of R
The sum of all the programming resistors should be
approximately 300kΩ as shown in Equation 8 otherwise
adjust the value of R
Equations 9, 10, 11 and 12 give the specific V
equations for the ISL62872 setpoint reference voltages.
V
R
R
R
R
SET X )
SET1
SET1
SET2
SET3
SET1
- V
- V
VID1
appears at the SREF pin
(
1
1
0
0
REF
SET(x)
, R
VID STATE
+
=
=
=
R
=
SET2
R
--------------------------------------------------------------------------------------------------- -
R
-----------------------------------------------------------------------------------------------------------
R
------------------------------------------------------------------------------- -
SET2
is the 500mV internal reference of the IC
SET4
SET4
SET4
V
TABLE 1. ISL62872 VID TRUTH TABLE
REF
is the resulting setpoint reference voltage that
, and R
+
SET4
VID0
⋅
⋅
⋅
⋅
R
1
0
1
0
KV
KV
(
SET
⎛
⎜
⎝
KV
SET3
1
V
KV
KV
SET4
SET4
SET4
+
REF
SET4
of approximately 100kΩ then calculate
SET3
SET2
SET3
amplifier:
--------- -
R
R
IN
+
F
⋅
R
⎞
⎟
⎠
⋅
⋅
KV
and repeat the calculations.
CLOSE
–
(
(
SET4
⋅
using Equations 5, 6, and 7
KV
KV
SW0
SW1
SW2
SW3
KV
KV
SET2
SET2
SET3
SET2
SET3
SET3
SET3
≅
300kΩ
SET
SET
–
–
)
is written as Equation 6:
is written as Equation 7:
V
KV
RESULT
REF
V
V
V
V
V
F
programming
SET2
amplifier to a
SREF
SET1
SET2
SET3
SET4
of the V
)
SET(x)
SET1
IN
)
SET
of the V
August 14, 2008
SET
where (x)
is written
gain
V
V
V
V
V
OUT1
OUT2
OUT3
OUT4
OUT
(EQ. 4)
FN6707.0
(EQ. 5)
(EQ. 6)
(EQ. 7)
(EQ. 8)
SET