Datasheet MAX889 (Maxim) - 6

High-Frequency, Regulated, 200mA, Inverting Charge Pump
(ESR) of the flying and output capacitors. The typical pump switching halts. Connect SHDN to IN or drive output impedance is more accurately determined from high for normal operation. the Typical Operating Characteristics.
Thermal Shutdown Current Limit and Soft-Start
The MAX889 features thermal shutdown with hysteresis The MAX889 features a foldback current-limit/soft-start for added protection against fault conditions. When the scheme that allows it to limit inrush currents during die temperature exceeds 160°C, the internal oscillator
MAX889
startup, overload, and output short-circuit conditions. stops, suspending device operation. The MAX889 Additionally, it permits a safe, timed recovery from fault resumes operation when the die temperature falls 15°C. conditions. This protects the MAX889 and prevents This prevents the device from rapidly oscillating around low-current or higher output impedance input supplies the temperature trip point. (such as alkaline cells) from being overloaded at start- up or short-circuit conditions.
Applications Information
The MAX889 features two current-limit/soft-start levels
Resistor Selection
with corresponding response to rising and falling out-
(Setting the Output Voltage)
put voltage thresholds of -0.6V and -1.5V. When the The accuracy of VOUT depends on the accuracy of the falling output voltage crosses -1.5V, such as during an voltage biasing R1 in Figure 1. Use a separate refer- overload condition, the input current is immediately lim- ence voltage if greater accuracy than provided by VIN ited to 400mA by weakening the charge-pump switch- is desired (Figure 4). Keep the feedback node as small es. When the falling output voltage crosses -0.6V, such as possible, with resistors mounted close to the FB pin. as during a short-circuit condition, the MAX889 further weakens the charge-pump switches, immediately limit- ing input current to 200mA. During startup or short-circuit recovery, the MAX889 S1 CAP+ S3 IN limits input current to 200mA with charge-pump switch- es at their weakest level. Rising output voltage crossing CFLY COUT S2 S4 -0.6V initiates a 2ms timer, after which the MAX889 OUT increases switch strength to the next level. The rising CAP- output voltage crossing -1.5V initiates a 2ms timer, after which the MAX889 provides full-strength operation. FOSC
Shutdown
When SHDN (a CMOS-compatible input) is driven low, the MAX889 enters 0.1µA shutdown mode. Charge- Figure 2. Charging CFLY INPUT 5.0V CIN R1 4.7µF 100k 1 S1 CAP+ S3 ON 6 IN 7 SHDN FB OFF IN R1 CFLY COUT 2 S2 S4 CAP+ MAX889T 66.5k C OUT FLY 5 OUTPUT 1µF OUT CAP- -3.3V 4 COUT CAP- 4.7µF FOSC GND 8 3 Figure 1. Typical Application Circuit. Figure 3. Transferring Charge on CFLY to COUT
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