ADP3051 データシートの表示（PDF） - Analog Devices
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ADP3051 Datasheet PDF : 16 Pages
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ADP3051
100% DUTY CYCLE OPERATION
The ADP3051 is capable of operating at 100% duty cycle, allow-
ing it to regulate output voltages that are very close to the input
voltage. In 100% duty cycle operation, the P-channel switch
remains continuously on, and the dropout voltage is simply the
output current multiplied by the on resistance of the internal
switch and inductor, typically 200 mV at full loads (500 mA).
SHUTDOWN
The ADP3051 is enabled and disabled via its SHDN input.
SHDN easily interfaces to open-drain and three-state logic
GPIOs. To enable the ADP3051, drive SHDN to within 0.5 V of
the voltage at IN; to disable the ADP3051, drive SHDN below
0.4 V. The circuit of Figure 18 shows a simple means of driving
SHDN to the proper high and low input states in cases where no
open-drain or three-state GPIO is available.
IN
100kΩ
SHDN
SHDN
CONTROL
ADP3051
Figure 18. Shutdown Control Circuit
UNDERVOLTAGE LOCKOUT (UVLO)
The ADP3051 includes an internal undervoltage lockout
(UVLO) circuit that turns off the converter if the input
voltage drops below the 2.2 V UVLO threshold. This prevents
uncontrolled behavior if the input voltage drops below the 2.7 V
minimum allowable voltage range. The UVLO circuit includes
55mV of hysteresis to prevent oscillation at the UVLO
threshold.
SHORT-CIRCUIT PROTECTION AND RECOVERY
When starting up or when the output is short circuited, the low
voltage drop across the synchronous rectifier may allow the
inductor current to run away because it rises more during the
on time than it falls during the off time. To protect against this,
the ADP3051 automatically initiates a frequency foldback
operation when the voltage at FB drops below 0.3 V, allowing
the ADP3051 to maintain control of the inductor current under
these conditions.
When operating at higher input voltages (for example, from a
5 V bus), the ADP3051 may exhibit output voltage overshoot
upon startup or after release of an overload condition (see
Figure 9). In such cases, the ADP3051’s limited COMP slew rate
can slow its recovery as the output approaches regulation,
allowing the output voltage to overshoot. If overshoot cannot be
tolerated in an application, the COMP voltage can be limited by
placing a Zener diode from COMP to GND, as shown in Figure 19.
COMP 6
CMPZ4683-ADC
ADP3051
Figure 19. COMP Zener Clamp to Prevent
Short-Circuit Recovery Output Voltage Overshoot
Rev. 0 | Page 10 of 16
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