ISL6522A Intersil Corporation, ISL6522A Datasheet - Page 5

• Manufacturer Part Number: ISL6522A
• Description: Buck and Synchronous Rectifier Pulse-Width Modulator (PWM) Controller
• Manufacturer: Intersil Corporation

monitored by the adaptive shoot through protection circuitry to
determine when the lower MOSFET has turned off.
PVCC
Provide a bias supply for the lower gate drive to this pin.
VCC
Provide a 12V bias supply for the chip to this pin.
Functional Description
Initialization
The ISL6522A automatically initializes upon receipt of
power. Special sequencing of the input supplies is not
necessary. The Power-On Reset (POR) function continually
monitors the input supply voltages and the enable (EN) pin.
The POR monitors the bias voltage at the VCC pin and the
input voltage (V
is equal to V
protection). With the EN pin held to V
initiates soft-start operation after both input supply voltages
exceed their POR thresholds. For operation with a single
+12V power source, V
+12V power source must exceed the rising V
before POR initiates operation.
The POR function inhibits operation with the chip disabled
(EN pin low). With both input supplies above their POR
thresholds, transitioning the EN pin high initiates a soft-start
interval.
Soft-Start
The POR function initiates the soft-start sequence. An internal
10µA current source charges an external capacitor (C
the SS pin to 4V. Soft-start clamps the error amplifier output
(COMP pin) to the SS pin voltage. Figure 3 shows the
soft-start interval. At t
voltages reach the valley of the oscillator’s triangle wave. The
oscillator’s triangular waveform is compared to the ramping
error amplifier voltage. This generates PHASE pulses of
increasing width that charge the output capacitor(s). This
interval of increasing pulse width continues to t2, at which
point the output is in regulation and the clamp on the COMP
pin is released. This method provides a rapid and controlled
output voltage rise.
IN
less a fixed voltage drop (see overcurrent
IN
) on the OCSET pin. The level on OCSET
1
IN
in Figure 3, the SS and COMP
and V
5
CC
are equivalent and the
CC
, the POR function
CC
threshold
SS
) on
ISL6522A
Overcurrent Protection
The overcurrent function protects the converter from a
shorted output by using the upper MOSFETs on-resistance,
r
converter’s efficiency and reduces cost by eliminating a
current sensing resistor.
The overcurrent function cycles the soft-start function in a
hiccup mode to provide fault protection. A resistor (R
programs the overcurrent trip level. An internal 200µA
(typical) current sink develops a voltage across R
DS(ON)
t
0
V
VOLTAGE
OSC(MIN)
15A
10A
4V
2V
5A
0A
0V
t
t
Where:
1
SoftStart
=
to monitor the current. This method enhances the
C
----------- V
I
FIGURE 4. OVERCURRENT OPERATION
SS
SS
FIGURE 3. SOFT-START INTERVAL
C
I
V
V
∆V
V
⋅
=
SS
t
OSC(MIN)
IN
OUTSteadyState
SS
1
OSC
t
OSC MIN
2
= Soft Start Current = 10µA
= Input Voltage
= Soft Start Capacitor
–
t
= Peak to Peak Oscillator Voltage = 1.9V
(
1
t
2
=
= Bottom of Oscillator = 1.35V
C
-----------
)
I
SS
TIME (20ms/DIV)
SS
RELEASED AT STEADY STATE
= Steady State Output Voltage
⋅
V
------------------------------------------------ ∆V
OUT
CLAMP ON V
SteadyState
V
IN
V
SOFT START
COMP
⋅
OCSET
V
COMP
V
OUT
OSC
OCSET
TIME
that
)