ISL8200AM Datasheet, PDF (17/24 Pages) Intersil Corporation – Complete Current Share 10A DC/DC Power Module

ISL8200AM
Figures 31 through 33. It is important to note that the OCP level
shown in these graphs is the average output current and not the
inductor ripple current.
16
14
1.8V_OUT
2.5V_OUT
12
10
1.2V_OUT
8
6
4
2
0
0
5
10
15
20
R_SEN (kΩ)
FIGURE 31. 5V_IN
16
14
5.0V_OUT
12
10
1.2V_OUT
1.8V_OUT
8
6
2.5V_OUT
4
2
0
0
10
20
30
40
50
R_SEN (kΩ)
FIGURE 32. 12V_IN
16
1.8V_OUT
14
12
10
1.2V_OUT
8
2.5V_OUT
6
4 ^5.0VOUT
2
0
0
20
40
60
R_SEN (kΩ)
FIGURE 33. 20V_IN
80
100
In a high input voltage, high output voltage application, such as
20V input to 5V output, the inductor ripple becomes excessive
due to the fixed internal inductor value. In such applications, the
output current will be limited from the rating to approximately
70% of the module’s rated current.
When OCP is triggered, the controller pulls EN low immediately to
turn off UGATE and LGATE.
For overload and hard short conditions, the overcurrent
protection reduces the regulator RMS output current much less
than full load by putting the controller into hiccup mode. A delay
time, equal to 3 soft-start intervals, is entered to allow the
disturbance to be cleared out. After the delay time, the controller
then initiates a soft-start interval. If the output voltage comes up
and returns to the regulation, PGOOD transitions high. If the OC
trip is exceeded during the soft-start interval, the controller pulls
EN low again. The PGOOD signal will remain low and the
soft-start interval will be allowed to expire. Another soft-start
interval will be initiated after the delay interval. If an overcurrent
trip occurs again, this same cycle repeats until the fault is
removed.
Fault Handshake
In a multi-module system, with the EN pins wired OR’ed together,
all modules can immediately turn off, at one time, when a fault
condition occurs in one or more modules. A fault would pull the
EN pin low, disabling all the modules and therefore not creating
current bounce. Thus, no single channel would be over stressed
when a fault occurs.
Since the EN pins are pulled down under fault conditions, the
pull-up resistor (R_UP) should be scaled to sink no more than 5mA
current from EN pin. Essentially, the EN pins cannot be directly
connected to VCC.
Oscillator
The Oscillator is a sawtooth waveform, providing for leading edge
modulation with 350ns minimum dead time. The oscillator
(Sawtooth) waveform has a DC offset of 1.0V. Each channel’s
peak-to-peak of the ramp amplitude is set to be proportional to
the voltage applied to its corresponding FF pin.
Frequency Synchronization and Phase Lock
Loop
The FSYNC_IN pin has two primary capabilities: fixed frequency
operation and synchronized frequency operation. By tying a
resistor (RFS) to PGND1 from the FSYNC_IN pin, the switching
frequency can be set at any frequency between 700kHz and
1.5MHz. The ISL8200AM has an integrated 59kΩ resistor between
FSYNC_IN and PGND1, which sets the default frequency to
700kHz. The frequency setting curve shown in Figure 34 is
provided to assist in selecting an externally connected resistor
RFS-ext between FSYNC_IN and PGND1 to increase the switching
frequency.
17
FN8271.2
September 13, 2012