B1077AS-4R7N AD [Analog Devices], B1077AS-4R7N Datasheet - Page 15

• Manufacturer Part Number: B1077AS-4R7N
• Description: 1.2 A, 20 V, 700 kHz/1.4 MHz, Nonsynchronous Step-Down Regulator
• Manufacturer: AD [Analog Devices]

SHORT-CIRCUIT PROTECTION
The ADP2300/ADP2301 include frequency foldback to prevent
output current runaway when there is a hard short on the output.
The switching frequency is reduced when the voltage at the FB pin
drops below a certain value, which allows more time for the
inductor current to decline, but increases the ripple current while
regulating the peak current. This results in a reduction in average
output current and prevents output current runaway. The corre-
lation between the switching frequency and the FB pin voltage
is shown in Table 5.
Table 5. Correlation Between the Switching Frequency
and the FB Pin Voltage
FB Pin Voltage
V
0.6 V > V
V
When a hard short (V
is initiated to regulate the output back to its level during normal
operation, which helps to limit the inrush current and prevent
possible overshoot on the output voltage.
FB
FB
≥ 0.6 V
≤ 0.2 V
FB
> 0.2 V
FB
≤ 0.2 V) is removed, a soft start cycle
Switching Frequency
f
½ f
¼ f
SW
SW
SW
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UNDERVOLTAGE LOCKOUT (UVLO)
The ADP2300/ADP2301 have fixed, internally set undervoltage
lockout circuitry. If the input voltage drops below 2.4 V, the
ADP2300/ADP2301 shut down and the MOSFET switch turns
off. After the voltage rises again above 2.8 V, the soft start
period is initiated, and the part is enabled.
THERMAL SHUTDOWN
If the ADP2300/ADP2301 junction temperature rises above 140°C,
the thermal shutdown circuit disables the chip. Extreme junction
temperature can be the result of high current operation, poor
circuit board design, or high ambient temperature. A 15°C
hysteresis is included so that when thermal shutdown occurs,
the ADP2300/ADP2301 do not return to operation until the on-
chip temperature drops below 125°C. After the devices recover
from thermal shutdown, a soft start is initiated.
CONTROL LOOP
The ADP2300/ADP2301 are internally compensated to minimize
external component count and cost. In addition, the built-in
slope compensation helps to prevent subharmonic oscillations
when the ADP2300/ADP2301 operate at a duty cycle greater
than or close to 50%.
ADP2300/ADP2301