ISL78220ANEZ Datasheet, PDF (19/22 Pages) Intersil Corporation – 6-Phase Interleaved Boost PWM Controller with Light Load Efficiency Enhancement

ISL78220
The ISL78220 also provides the flexibility for output overvoltage
protection by utilizing the VOUT_SEN and VOUT_OVB pins. The
VOUT_SEN pin is used for sensing the output voltage. A resistor
divider network is connected between this pin and the boost
power stage output voltage rail. When the voltage on VOUT_SEN
is higher than 2.4V, the open drain output VOUT_OVB will be
pulled low, and the ISL78220 IC will be latched off to indicate an
output overvoltage condition. The V_OUT overvoltage sensing
threshold can be programmed by changing the resistor values.
Overcurrent Protection
ISL78220 has two levels of overcurrent protection. Each phase is
protected from an overcurrent condition by limiting its peak
current, and the combined total current is protected on an
average basis.
For the individual channel overcurrent protection, the ISL78220
continuously compares the CSA output current of each channel
with a 160µA reference current. If any channel’s current trips the
current limit comparator, the ISL78220 will be shut down.
However, during the phase adding period, the individual channel
current protection function will be blanked for 200µs, in order to
give other phases the chance to take care of the current.
IOUT pin serves for both input current monitoring and total
average current OCP functions. The CSA output current for each
channel is scaled and summed together at this pin. An RC
network should be connected between IOUT pin and GND, such
that the ripple current signal can be filtered out and converted to
a voltage signal to represent the averaged total input current. The
relationship between total input current I_IN and V_IOUT can be
calculated as Equation 10: (Please refer to Figure 20 for RSEN
and RSET positions).
V_IOUT
=
0.75 I_{I N}
R_{-----S---E---N--}
R_SET
R_IO
UT
(EQ. 10)
When the V_IOUT is higher than 2V for a consecutive 100µs, the
ISL78220 IC will be triggered to shut down. This provides
additional safety for the voltage regulator.
Equation 11 can be used to calculate the value of the resistor R_IOUT
based on the desired OCP level I_{AVG, OCP2}.
R_IOUT
=
-------------²--------------
I_{AVG, OCP2}
(EQ. 11)
The total average overcurrent protection scheme will not be
asserted until the soft-start pin voltage V_SS reaches its clamped
value (approximately 3.5V). During the soft-start time the system
does not latch-off if per-channel or overall OC limit is reached.
Instead the individual channel current will run at its pre-set peak
current limit level.
Thermal Protection
The ISL78220 will be disabled if the die junction temperature
reaches a nominal of +160°C. It will recover when the junction
temperature falls below a +15°C hysteresis. The +15°C
hysteresis insures that the device will not be re-enabled until the
junction temperature has dropped to below about +145°C.
Internal 5V LDO Output Current
Limit Derating Curves
ISL78220 contains an internal 5V/200mA LDO, and the input of
LDO (VIN pin) can go as high as 40V. Based on the junction to
ambient thermal resistance R_JA of the package, we need to
guarantee that the maximum junction temperature should be
below +125°C T_MAX. Figure 22 shows the relationship between
maximum allowed LDO output current and input voltage. The
curve is based on +35°C/W thermal resistance R_JA for the
package, different curve represents different ambient
temperature T_A.
FIGURE 22. I_LDO(MAX) vs V_IN
Dedicated VREF2 Pin for Input
Voltage Tracking
A second reference input pin, VREF2, is added to the input of the
transconductance amplifier. The ISL78220 internal reference will
automatically change to VREF2 when it is pulled below 1.8V. The
VREF2 pin can be connected to VIN through resistor network to
implement the automatic input voltage tracking function. This
function is very useful under car battery voltage cranking
conditions (such as when the car is parked and the driver is
listening to the stereo), where the full load power is typically not
needed. In this case, the ISL78220 can limit the output power by
allowing the output voltage to track the input voltage. If VREF2 is
not used, the pin should be connected to VCC.
Configurations for 12-Phase
Operation
For high power applications, two ISL78220 ICs can be easily
configured to support 12-phase operation. The IC that provide the
CLK_OUT signal is called master IC, and the IC that received the
CLK_OUT signal is called slave IC. Note that the two PWM1
signals are synchronized and the net effect is 6-phase operation
with double the output current.
19
FN7688.3
December 24, 2013