Datasheet MAX1735 (Maxim) - 7

200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23 MAX1735
-5.5V TO -1.25V -5.0V,-3.0V, OR -2.5V -6.5V TO -2.5V ADJUSTABLE -6.5V TO -2.5V FIXED INPUT OUTPUT INPUT OUTPUT IN OUT IN OUT CIN COUT CIN C 1 OUT µF CERAMIC R1 1µF 1µF CERAMIC 1µF CERAMIC CERAMIC MAX1735 MAX1735 ON ON GND OFF SHDN SET GND OFF SHDN SET ON ON GND GND R2 VOUT = VSET (1 + R1) R2 Figure 2. Typical Application Circuit with Preset Output Voltage Figure 3. Typical Application Circuit with Adjustable Output Voltage In adjustable mode, an output voltage between -5.5V and -1.25V is selected using two external resistors connected
Current Limiting
as a voltage-divider from OUT to SET (Figure 3). The out- The MAX1735 features a current limit that protects the put voltage is determined by the following equation: regulator. Short-circuit output current is typically 515mA. The output will withstand a short to ground  R1  indefinitely; however, if the increased power dissipation V = V OUT SET 1+   R2  heats the die to +160°C, the thermal overload protec-   tion will shut off the regulator, preventing damage to the where VSET = VREFERENCE = -1.25V when in regulation. IC. Since the input bias current at SET is <100nA, use large resistance values for R1 and R2 to minimize
Thermal Overload Protection
power consumption in the feedback network. A typical The thermal overload protection circuit protects the reg- value of 100kΩ for R2 is acceptable for most applica- ulator against overheating due to prolonged overload tions. Higher values consume less current at the conditions. When the die temperature exceeds +160°C, expense of output voltage accuracy. The above equa- an on-chip thermal sensor disables the pass transistor, tion solved for R1 is: allowing the IC to cool. The thermal sensor reenables the pass MOSFET once the die temperature drops   V   15°C. A continuous short-circuit fault condition results in R1= R OUT 2  1 a cyclical enabling and disabling of the output.  V  SET  −   Thermal overload protection is designed to safeguard For preset output voltage mode, connect SET directly the MAX1735 in the event of overload fault conditions. to GND. For normal operation, do not exceed the absolute maxi- mum junction temperature rating of +150°C. Junction
Shutdown
temperature is greater than ambient by an amount In shutdown, the N-channel MOSFET, control circuitry, depending on package heat dissipation and the ther- reference, and all internal circuits are turned off, reduc- mal resistance from the junction to ambient (θJA): ing supply current to typically 1nA. SHDN can be dri- T ven by either a positive or negative voltage. Drive JUNCTION = TAMBIENT + (θJA)(PDISSIPATION) SHDN above +1.6V or below -1.6V to turn the regulator where on. To turn the regulator off, drive SHDN to GND. For θJA for the 5-pin SOT23 is about 0.140°C/mW. always-on operation, connect SHDN to IN. By including a positive threshold at SHDN, it can be driven by a standard 5V TTL level without needing level-shifting cir- cuitry.
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