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High Efficiency . . . 60% or Greater

Peak Switch Current . . . 500 mA

Input Current Limit Protection

TTL-Compatible Inhibit

Adjustable Output Voltage

Input Regulation . . . 0.2% Typ

Output Regulation . . . 0.4% Typ

Soft Start-Up Capability

Can be Used in Buck, Boost, and

Inverting Configurations

description/ordering information

The TL497A incorporates all the active functions required in the construction of switching voltage regulators.

It also can be used as the control element to drive external components for high-power-output applications. The

TL497A was designed for ease of use in step-up, step-down, or voltage-inversion applications requiring high

efficiency.

The TL497A is a fixed-on-time variable-frequency switching-voltage-regulator control circuit. The switch-on

time is programmed by a single external capacitor connected between FREQ CONTROL and GND. This

capacitor, CT, is charged by an internal constant-current generator to a predetermined threshold. The charging

current and the threshold vary proportionally with VCC. Thus, the switch-on time remains constant over the

specified range of input voltage (4.5 V to 12 V). Typical on times for various values of CT are as follows:

The output voltage is controlled by an external resistor ladder network (R1 and R2 in Figures 1, 2, and 3) that

provides a feedback voltage to the comparator input. This feedback voltage is compared to the reference

voltage of 1.2 V (relative to SUBSTRATE) by the high-gain comparator. When the output voltage decays below

the value required to maintain 1.2 V at the comparator input, the comparator enables the oscillator circuit, which

charges and discharges CT as described above. The internal pass transistor is driven on during the charging

of CT. The internal transistor can be used directly for switching currents up to 500 mA. Its collector and emitter

are uncommitted, and it is current driven to allow operation from the positive supply voltage or ground. An

internal Schottky diode matched to the current characteristics of the internal transistor also is available for

blocking or commutating purposes. The TL497A also has on-chip current-limit circuitry that senses the peak

currents in the switching regulator and protects the inductor against saturation and the pass transistor against

overstress. The current limit is adjustable and is programmed by a single sense resistor, RCL, connected

between VCC and CUR LIM SENS. The current-limit circuitry is activated when 0.7 V is developed across RCL.

External gating is provided by the INHIBIT input. When the INHIBIT input is high, the output is turned off.

Simplicity of design is a primary feature of the TL497A. With only six external components (three resistors, two

capacitors, and one inductor), the TL497A operates in numerous voltage-conversion applications (step-up,

step-down, invert) with as much as 85% of the source power delivered to the load. The TL497A replaces the

TL497 in all applications.

The TL497AC is characterized for operation from 0°C to 70°C. The TL497AI is characterized for operation from

?40°C to 85°C.