Datasheet MAX8863, MAX8864 (Analog Devices) - 7

link to page 3 link to page 3 link to page 7 link to page 3 MAX8863T/S/R, Low-Dropout, 120mA Linear Regulators MAX8864T/S/R Choose R2 = 100kΩ to optimize power consumption, accuracy, and high-frequency power-supply rejection. The OUTPUT total current through the external resistive feedback and VOLTAGE IN OUT load resistors should not be less than 10μA. Since the
MAX8863
VSET tolerance is typically less than ±25mV, the output can
MAX8864
R1 20pF be set using fixed resistors instead of trim pots. Connect SHDN SET a 10pF to 25pF capacitor across R1 to compensate for CIN RL BATTERY COUT 1µF layout-induced parasitic capacitances. GND R2 1µF In preset voltage mode, impedances between SET and ground should be less than 100kΩ. Otherwise, spurious conditions could cause the voltage at SET to exceed the 60mV Dual Mode threshold.
Shutdown
Figure 2. Adjustable Output Using External Feedback A low input on the SHDN pin shuts down the MAX8863/ Resistors MAX8864. In shutdown mode, the pass transistor, control
Internal p-Channel Pass Transistor
circuit, reference, and all biases are turned off, reducing The MAX8863/MAX8864 feature a 1.1Ω typical pMOSFET the supply current to typically 0.1nA. Connect SHDN to pass transistor. This provides several advantages over IN for normal operation. The MAX8864 output voltage is similar designs using PNP pass transistors, including actively discharged to ground when the part is placed in longer battery life. shutdown (see Typical Operating Characteristics). The pMOSFET requires no base drive current, which
Current Limit
reduces quiescent current considerably. PNP-based The MAX8863/MAX8864 include a current limiter that regulators waste considerable amounts of current in monitors and controls the pass transistor’s gate voltage, dropout when the pass transistor saturates. They also estimating the output current and limiting it to about use high base-drive currents under large loads. The 280mA. For design purposes, the current limit should be MAX8863/MAX8864 do not suffer from these problems, considered 120mA (min) to 420mA (max). The output can and consume only 80μA of quiescent current, whether in be shorted to ground for an indefinite time period without dropout, light load, or heavy load applications (see Typical damaging the part. Operating Characteristics).
Thermal Overload Protection Output Voltage Selection
Thermal overload protection limits total power dissipation The MAX8863/MAX8864 feature Dual Mode operation: in the MAX8863/MAX8864. When the junction temperature they operate in either a preset voltage mode or an adjustable exceeds TJ = +170°C, the thermal sensor sends a signal mode. to the shutdown logic, turning off the pass transistor and In preset voltage mode, internal, trimmed feedback resistors allowing the IC to cool. The thermal sensor will turn the set the MAX886_R output to 2.80V, the MAX886_S output pass transistor on again after the IC’s junction temperature to 2.84V, and the MAX886_T output to 3.15V. Select this typically cools by 20°C, resulting in a pulsed output during mode by connecting SET to ground. continuous thermal overload conditions. In adjustable mode, select an output between 1.25V and Thermal overload protection is designed to protect the 6.5V using two external resistors connected as a voltage MAX8863/MAX8864 in the event of fault conditions. divider to SET (Figure 2). The output voltage is set by the Stressing the device with high load currents and high following equation: input-output differential voltages (which result in die temperatures above +125°C) may cause a momentary VOUT = VSET (1 + R1 / R2) overshoot (2% to 8% for 200ms) when the load is where VSET = 1.25V. To simplify resistor selection: completely removed. This can be remedied by raising the minimum load current from 0μA (+125°C) to 100μA (+150°C).  VOUT  R1 For continuous operation, do not exceed the absolute = R2  1 −   VSET  maximum junction temperature rating of TJ = +150°C. www.maximintegrated.com Maxim Integrated │ 7