ACT4527
Rev 2, 06-Jan-2017
FUNCTIONAL BLOCK DIAGRAM
HSB
VIN
UVLO
PWM
Controller
PDC
70mΩ
SW
Driver
4.7Ω
Current Sense
and Control
OVP
CSP
CSN
GND
FUNCTIONAL DESCRIPTION
Output Under-Voltage Protection /
Hiccup Mode
Output Current Sensing and Regulation
Sense resistor is connected to CSP and CSN. The
sensed differential voltage is compared with interval
reference to regulate current. CC loop and CV loop
are in parallel. The current loop response is allowed
to have slower response compared to voltage loop.
However, during current transient response, the
inductor current overshoot/undershoot should be
controlled within +/-25% to avoid inductor
saturation.
There is
a
under voltage protection (UVP)
threshold. If the UVP threshold is hit for 10us, an
over current or short circuit is assumed, and the
converter goes into hiccup mode by disabling the
converter and restarts after hiccup waiting period.
Cord Compensation
In some applications, the output voltage is
increased with output current to compensate the
potential voltage drop across output cable. The
compensation is based on the high side feedback
resistance.
Cycle-by-Cycle Current Control
The conventional cycle-by-cycle peak current mode
is implemented with high-side FET current sense.
Input Over Voltage Protection
The compensation voltage is derived as:
ÄVout = (VCSP-VCSN)*K
The converter is disabled if the input voltage is
above 42V (+/-2V). Device resumes operation
automatically 40ms after OVP is cleared.
Where K=3.03
This voltage difference could be added on the
reference or turning the (VCSP-VCSN) voltage into a
sink current at FB pin to pull Vout higher than
programmed voltage.
Output Over Voltage Protection
Device stops switching when output over-voltage is
sensed, and resumes operation automatically when
output voltage drops to OVP- hysteresis.
The cord compensation loop should be very slow to
avoid potential disturbance to the voltage loop. The
voltage loop should be sufficiently stable on various
cord compensation setting.
Output Over Voltage Discharge
Discharge circuit starts to discharge output through
CSP pins when output over voltage is detected.
Discharge circuit brings 12V down to 5V in less
than 100ms.
Thermal Shutdown
If the TJ increases beyond 160°C, ACT4527 goes
into HZ mode and the timer is preserved until TJ
drops by 30°C.
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