ISL6144 Datasheet, PDF (16/29 Pages) Intersil Corporation – High Voltage ORing MOSFET Controller

ISL6144
DC/DC Converter Power Board (not part of the
ISL6144EVAL1 board)
The DC/DC converter board consists of two DC/DC
converters with independent input voltage rails. In reality, two
identical power supplies can be used in the test setup to
replace this board (contact Intersil Applications Engineering
if you need assistance in your test setup). This DC/DC
converter board is configured for operation at different output
voltage levels depending on the choice of DC/DC modules.
Most evaluation results are provided for a mix of +48V and
+12V input voltages. Any other voltage within the +9V to
+75V range can also be used.
Each DC/DC converter has a low r_DS(ON) MOSFET
connected in parallel to the output terminals. This MOSFET
is normally off. When turned on it simulates a short across
the output. Another MOSFET is connected at the ON/OFF
pin of the modules to simulate a slow turn-off of the module.
Single-Feed Evaluation
The ISL6144EVAL1 is hooked up to two input power
supplies using test setup shown in Figure 16 or Figure 17.
Note that the ISL6144EVAL1 is populated with one
FDB3632 MOSFET per feed (Nominal value of the
MOSFET’s r_DS(ON) is approximately 8mΩ at V_GS = 10V).
1. Connect the input power supplies, auxiliary 5V power
supply, load and output capacitor to the ISL6144EVAL1.
2. Connect test equipment (Oscilloscope, DMM) to the
signals of interest using on-board test points and scope
probe jacks.
3. Turn-on PS1 with V_IN1 = +48V (V_IN1 can be any voltage
within +9V to +75V). Turn-on the auxiliary power supply
(AUX PS powering the LED circuit) with +5V. Adjust load
current to 2A. Verify the main operational parameters
such as the 20mV forward regulation at light loads, and
gate voltage as a function of load current.
4. The forward voltage drop across the MOSFET terminals
V_SD1 (TP1-TP2) is equal to the maximum of the 20mV
forward regulated voltage drop across the source-drain
“V_{FWD_HR}“ or the product of the load current and the
MOSFET on-state resistance “I_Load * r_DS(ON)”.
5. For I_Load = 2A, V_SD1 is equal to V_{FWD_HR} = 20mV. The
gate-source voltage is modulated as a function of load
current and MOSFET transconductance. Gate-source
voltage V_GS1 (TP13 -TP17) is approximately 4V. In this
case, LED1 is off. LED2 will be RED as V_IN2 is still off.
6. Increase the load current I_Load to 4A. Note that V_DS1 is
increased to above V_{FWD_HR} and operation in the 20mV
forward regulation cannot be maintained. The MOSFET
cannot deliver the required load current with a 20mV
constant V_SD1. In this case, gate voltage is fully charge-
pumped to V_GQP (10.6V nominal).
7. Turn-off V_IN1 and turn-on V_IN2 and repeat the same tests
listed above. Make sure the ISL6144 is providing gate
voltage, which is modulated based on the load current.
V_SD2 is measured between (TP4-TP5), V_GS2 is
measured between (TP14-TP21).
Two-Feed Parallel Evaluation
Two Feed parallel operation verification can be performed
after completion of the single feed evaluations. Make sure
that the two Input power supplies connected to the
ISL6144EVAL1 board are identical in voltage value. Identical
input voltages are needed to enable the two feeds to share
the load current (In real world power systems, current
sharing is most likely insured by the power supplies/modules
that have an active current sharing feature).
1. Turn-on PS1 and PS2 in sequence (hot plugging is not
recommended). Adjust V_IN1 and V_IN2 close to each
other. Verify the input current of both feeds to be within
acceptable current sharing accuracy (~10%). Current
sharing accuracy will be very poor at light loads and
becomes better with higher load currents.
2. Adjust the load current to different values and verify that
both V_SD1 (TP1 to TP2) and V_SD2 (TP4 to TP5) are close
to each other. These two voltages might be different
depending on the amount of load current passing through
each of the two feeds.
3. At light loads, I_Load * r_DS(ON) is less than 20mV, the
ISL6144 operates in the forward regulation mode and
gate voltage is modulated as a function of load current.
When I_Load*r_DS(ON) becomes higher than the regulated
20mV, the charge pump increases and clamps the gate
voltage to the maximum possible charge pump voltage,
V_GQP.
4. Verify the Gate voltage of both MOSFETs V_GS1 (TP13 to
TP17) and V_GS2 (TP14 to TP21) with different load
currents.
5. Both LED1 and LED2 are off when both feeds are on.
6. For I_Load = 4A, turn-off V_IN2 and note that V_GS2 has
turned off. LED2 is RED and V_GS1 has increased from
around 4V to V_GQP.
7. Turn V_IN2 back on and turn V_IN1 off. V_GS1 is now off.
LED1 is RED. V_GS2 has increased to V_GQP.
Performance Tests
Performance tests can be carried out after the two feeds
have been verified and found to be operational in active,
1 + 1 redundancy (when two feeds share the load current,
current sharing is ensured by the incoming power supplies.)
These include gate turn-on at power supply start-up, fast
speed turn-off (in case of fast dropping input rail), slow
speed turn-off (in response to slow dropping input rail) and
fault detection in response to different faults.
Gate Start-Up Test
FIRST-FEED START-UP
When the first feed is turned on, as V_IN1 rises, conduction
occurs through the body diode of the MOSFET. This only
occurs for a short time until the MOSFET gate voltage can
be charge-pumped on. This conduction is necessary for
proper operation of the ISL6144. It provides bias for the gate
hold off and other internal bias and reference circuitry. The
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FN9131.5
October 8, 2010