2
To observe the output while the regulator sinks current,
connect the positive terminal of the load to the 3.3V post
(J1). Connect the return terminal of the same load to the
V
OUT
post (J3).
Startup
There are two distinct start up methods for both the ISL6526
and ISL6527 regulators. The first method is invoked through
the application of power to the IC. The soft-start feature
allows for a controlled rise of the output once the Power On
Reset (POR) threshold of the input voltage has been
reached. Figure 1 shows the start up profile of the regulator
in relation to the start up of the 3.3V input supply and the
bias supply generated by the charge pump. Both the
ISL6526 and ISL6527, whether switching at 300 or 600kHz,
will have the same start up profile as shown in Figure 1.
The second method of start up is through the use of the
Enable/Shutdown feature. Holding the ENABLE pin on the
ISL6526 or the OCSET/SD pin on the ISL6527 below 0.8V
will disable the regulator by forcing both the upper and lower
MOSFETs off. Releasing the respective pin allows the
regulator to start up. Figure 2 shows the start up profile with
this method.
Shutdown
As discussed in the previous section, if the OCSET/SD pin
or ENABLE pin is pulled down and held below 0.8V, the
regulator will be turned off. The MOSFET gates are
immediately pulled low. Figure 3 shows the shutdown profile
of the regulator under full load.
ISL6527 Input Reference
A distinguishing feature of the ISL6527 is that the reference
used to regulate the output is provided from an external
source. This allows the converter to track the output of
another regulator at any desired ratio or amplify a small
signal. Figure 4 illustrates the tracking and power
amplification ability of the ISL6527 with a sinusoidal
reference. Figure 4 also illustrates the startup profile.
Ripple Voltage
Figure 5 shows the ripple voltage on the output of the
regulator. The ripple voltages shown are for both the
ISL6526 and ISL6527 ICs running at either 300 or 600kHz.
FIGURE 1. START UP FROM POR
2ms/DIV
V
CPVOUT
1V/DIV
V
VCC
1V/DIV
V
OUT
1V/DIV
FIGURE 2. START UP FROM SHUT DOWN
1ms/DIV
V
OUT
1V/DIV
V
ENABLE
1V/DIV
FIGURE 3. SHUTDOWN WITH FULL LOAD (ISL6526)
20
µ
s/DIV
V
ENABLE
1V/DIV
V
OUT
1V/DIV
FIGURE 4. SMALL SIGNAL POWER AMPLIFICATION
2ms/DIV
V
REF_IN
200mV/DIV
V
OUT
200mV/DIV
AN1021
