ST755

· 2.7V TO 11V INPUT TO ADJUSTABLE NEGATIVEOUTPUT CONVERSION
· 1W GUARANTEED OUTPUT POWER
     (Vin>4.5V, T370oC)
· 68% TYP. EFFICENCY AT6V
· VERYLOW QUIESCENT CURRENT: 1.2mAIN ON MODE 10mA IN SHUT DOWN MODE
· SOFT START
· VERYLOW NOISE OUTPUT
· 160KHz FIXEDFREQUENCY OSCILLATOR
· MIXED BIPOLAR-CMOS TECHNOLOGY

The ST755 is an IC developed for voltage conversion from an input voltage ranging from +2.4V to 11V to a regulated adjustable negative output limited by |V_out| 12.7V-V_IN. The circuit adopts a current-mode PWM control scheme to achieve good efficiency , high stability and low noise performance. The figure in the first page shown the detailed block diagram of the device. ST755 is realized in a BCD technology in order to achieve high temperature stability, the best REFERENCE precision , a very low quiescent current and jitter free operations. The final stage is built around a 0.7 - 2A P-Channel Power MOS. A fraction of the output current is splitted out for current detection.Internal clock frequencyis fixed to 160KHz. Error amplifier drives the PWM comparator in order to keep 0V on the CC input. So R3 and R4 resistors are calculated by the following formulae R₄ = (|V_out|/V_ref)*R3 (see fig 1). For R₃ can be choosen any value between 2K and 20K. Soft-Start (SS) input is a voltage dependent-output current limit (see figure 9, Switch Current Limit vs. SS Input Voltage). SS pin is internally pulled to Vref through a 1.2 M resistor. Applying an appropiate capacitor at SS input is possible to obtain a soft-start current limitation during power up. Forcing Soft-Start (SS) input to a lower voltage through a resistive voltage driver (R₁ and R₂), the maximum LX curent limit can be lowered according the diagram showed in figure 9. When SHDN input islow, the total current consumption is reduced to 10A.

Absolute Maximum Rating are those values beyond which damage to the device may occur.
Functional operation under these condition is not implied.

The ST755 is an adjustable inverting switch-mode DC-DC rergulator with internal Power MOSFET that generaters an adjustable negative output from a voltage input of 2.7V to 11V, output current guaranteed at 200mA (for V_in>4.5V, V_out = -5V and 0^oC 3 T_a 3 70^oC) and 275mA (typical value at T_a = 25 ^oC, V_out = -5V). A logic controlled shut down pin that interfaces directly with microprocessor reduces supply current to only 10mA. Input to Output differential voltage is limited to V_in+|V_out|<12.7V. No load supply current is 1.2mA.