ISL6529CR Intersil, ISL6529CR Datasheet - Page 9

• Manufacturer Part Number: ISL6529CR
• Description: IC CTRLR PWM DUAL REG 16-QFN
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of ISL6529CR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.5 ~ 4.5 V
• Frequency - Switching: 600kHz
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-VQFN Exposed Pad, 16-HVQFN, 16-SQFN, 16-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Input: -
• Power - Output: -

However, since the value of R1 affects the values of the rest
of the compensation components, it is advisable to keep its
value less than 5kΩ. Depending on the value chosen for R1,
R4 can be calculated based on the following equation:
If the output voltage desired is 0.8V, simply route VOUT1
back to the FB pin through R1, but do not populate R4.
The linear regulator output voltage is also set by means of
an external resistor divider as shown in Figure 5. The two
resistors used to set the output voltage should not exceed a
parallel equivalent value, referred to as R
restriction is due to the manner of implementation of the soft-
start function. The following relationship must be met:
R4
R
+3.3V
V
FIGURE 5. OUTPUT VOLTAGE SELECTION OF THE LINEAR
C
FB
OUT2
V
For frequency compensation considerations
FIGURE 4. OUTPUT VOLTAGE SELECTION OF THE PWM
set R5 to 4.64k and adjust R6 for the required voltage.
C
OUT2
V
=
OUT2
OUT1
OUT1
IN
=
------------------------------------- -
V
+
R5
--------------------- -
R5
OUT1
R1
=
+
×
+
R3
×
R6
R6
0.8
0.8V
–
0.8V
<
×
5kΩ


L
Q3
C3
1
R1
OUT
+
R4
R5
------- -
R6


R5
R2
R12
Q1
Q2
+3.3V
C2
9
R6
C1
C4
DRIVE2
UGATE
LGATE
FB2
COMP
FB
FB
+12V
12VCC
, of 5kΩ. This
ISL6529A
ISL6529A
ISL6529
ISL6529
5VCC
+5V
ISL6529, ISL6529A
(EQ. 1)
(EQ. 2)
To ensure the parallel combination of the feedback resistors
meets this criteria, choose a target value for R
5kΩ and then apply the following equations:
where V
and V
output voltage of 0.8V, simply populate R5 with a value less
than 5kΩ and do not populate R6.
Converter Shutdown
Pulling and holding the FB2 pin above a typical threshold of
1.28V will shut down both regulators. Upon release of the
FB2 pin, the regulators enter into a soft-start cycle which
brings both outputs back into regulation.
PWM Controller Feedback Compensation
A simplified representation of the voltage-mode control loop
used for output regulation by the converter is shown in
Figure 6. The output voltage, V
negative input of the error amplifier which is regulated to the
reference voltage level, V
V
oscillator, V
signal from the PWM comparator. This signal is then used to
switch the MOSFET and produce a PWM waveform with an
amplitude of V
PHASE voltage is then smoothed by the output filter, L
and C
The modulator transfer function is defined as V
The internal PWM comparator and driver circuits equate to a
DC gain block dominated by the supply voltage, V
by the peak-to-peak magnitude of the triangle wave,
The output filter components, L
overall modulator small-signal transfer function by
contributing a double pole break frequency at F
zero at F
R5
R6
E/A
=
=
, is compared with the triangle wave produced by the
REF
OUT
V
------------------ -
----------------------------------------
V
V
OUT2
OUT2
R5
OUT2
REF
ESR
, to produce a DC voltage level.
is the internal reference voltage, 0.8V. For an
×
OSC
V
.
×
–
is the desired linear regulator output voltage
IN
REF
V
R
, to provide a pulse-width modulated (PWM)
REF
FB
at the PHASE node. The square-wave
REF
. The error amplifier output,
OUT
OUT
, is fed back to the
and C
OUT
FB
, shape the
OUT
LC
of less than
IN
and a
April 12, 2005
/V
, divided
∆
E/A
(EQ. 3)
(EQ. 4)
V
FN9070.5
OUT
OSC
.
.