ISL6549CAZA-T Intersil, ISL6549CAZA-T Datasheet - Page 9

• Manufacturer Part Number: ISL6549CAZA-T
• Description: IC CTRLR PWM SYNC BUCK 16-QSOP
• Manufacturer: Intersil

Specifications of ISL6549CAZA-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 2
• Frequency - Max: 1MHz
• Duty Cycle: 100%
• Voltage - Supply: 4.75 V ~ 13.2 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 16-QSOP
• Frequency-max: 1MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ISL6549CAZA-TTR

soft-start cycles (1 internal soft-start ramp cycle, plus
one-quarter on the next).
If either V
UV shutdown and restart cycle; similarly, if either V
removed after start-up, a shutdown and restart cycle will start
when its output drifts down to the UV trip point. But in both
cases, once the V
the next soft-start ramp.
Figure 5 shows an example of the start-up, with V
powered. V
time the UV comparators are enabled. Since V
present, V
and it will fail the test for UV, shutting down both outputs. It
starts an internal delay time-out (equal to one soft-start
interval), and then starts a new ramp. For this example, it
shows about a 1.6ms ramp up, and 6.4ms off, before the next
ramp starts. Thus, the total period of 8ms is based on 1.25
soft-start cycles (one-quarter of the first ramp, and then one
full time-out, at a clock period of around 1.6µs) The dotted
magenta line shows the case where V
ramp all of the way up to 2V.
Switching Frequency
The switching frequency of the ISL6549 is determined by the
value of the FS resistor. The graph in Figure 6 shows the
GND>
GND>
FIGURE 5. UNDERVOLTAGE PROTECTION (SIMULATED BY
100k
1M
1.6ms
INx
10k
OUT1
FIGURE 6. FREQUENCY vs FS RESISTOR
OUT2
voltage is not present at startup, that will cause a
HAVING NO VIN1 ON POWER-UP)
will not be following the soft-start ramp up,
ramps up one-quarter of the way, at which
V
V
INx
OUT2
OUT1
6.4ms
is restored, the V
(0.5V/DIV)
(0.5V/DIV)
R (kΩ)
100k
9
OUT2
OUTs
is allowed to
V
will recover on
OUT2
IN1
IN1
1M
(0.5V/DIV)
is not
INx
not
is
ISL6549
dependence between the resistor chosen and the resulting
switching frequency.
Output Voltage Selection
The output voltage of the PWM converter can be programmed
to any level between V
However, even though the ISL6549 can run at near 100%
duty cycle at zero load, additional voltage margin is required
above V
used to scale the output voltage relative to the reference
voltage and feed it back to the inverting input of the error
amplifier (see Figure 7). A typical value for R1 may be 1.00kΩ
(±1% for accuracy), and then R4 (also ±1%) is chosen
according to Equation 1:
R1 is also part of the compensation circuit (see “PWM
Controller Feedback Compensation” on page 10 for more
details), so once chosen for that, it should not be changed to
adjust V
is 0.8V, simply route V
but do not populate R4. V
reference are not available.
The linear regulator output voltage is also set by means of
an external resistor divider as shown in Figure 8. Select a
value for R5 (typical 1.00kΩ ±1% for accuracy), and use
Equation 2 to calculate R6 (also ±1%), where V
desired linear regulator output voltage and V
internal reference voltage, 0.8V. For an output voltage of
0.8V, simply populate R5 with a value less than 5kΩ and do
not populate R6. V
reference are not available.
R4
R
6
FIGURE 7. OUTPUT VOLTAGE SELECTION OF THE
C
=
=
V
OUT1
OUT1
-------------------------------------- -
V OUT
--------------------------------------- -
V OUT1 0.8V
OUT1
IN1
R
R1 0.8V
+
5
R3
to allow for loading. An external resistor divider is
×
×
; only change R4. If the output voltage desired
SWITCHER (V
2
0.8V
–
–
0.8V
L
OUT2
C3
R1
OUT
C
R4
IN1
IN1
OUT1
voltages less than the 0.8V
OUT1
and the internal reference, 0.8V.
+
OUT1
R2
back to the FB pin through R1,
Q2
Q1
V
C2
IN1
voltages less than the 0.8V
)
V
C1
OUT1
=
0.8
UGATE
PHASE
LGATE
FB
COMP
REF
×
September 22, 2006
ISL6549
⎛
⎝
1
OUT2
+
is the
R1
------- -
R4
⎞
⎠
(EQ. 1)
(EQ. 2)
FN9168.2
is the