TL497A Datasheet, PDF (1/9 Pages) Texas Instruments – SWITCHING VOLTAGE REGULATORS

TL497A
SWITCHING VOLTAGE REGULATORS
SLVS009D – JUNE 1976 – REVISED JULY 1999
D High Efficiency . . . 60% or Greater
D Output Current . . . 500 mA
D Input Current Limit Protection
D TTL-Compatible Inhibit
D Adjustable Output Voltage
D Input Regulation . . . 0.2% Typ
D Output Regulation . . . 0.4% Typ
D Soft Start-Up Capability
D, N, OR PW PACKAGE
(TOP VIEW)
COMP INPUT 1
INHIBIT 2
FREQ CONTROL 3
SUBSTRATE 4
GND 5
CATHODE 6
ANODE 7
14 V_CC
13 CUR LIM SENS
12 BASE DRIVE^†
11 BASE^†
10 COL OUT
9 NC
8 EMIT OUT
description
The TL497A incorporates all the active functions
required in the construction of switching voltage
NC – No internal connection
† _{BASE (11) and BASE DRIVE (12) are used for device testing}
only. They normally are not used in circuit applications of the
device.
regulators. It can also 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, C_T, is charged by an internal constant-current generator to a predetermined threshold. The charging
current and the threshold vary proportionally with V_CC. 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 C_T are as follows:
TIMING CAPACITOR, CT (pF)
ON TIME (µs)
200
250
350
400
500
750 1000 1500 2000
19
22
26
32
44
56
80
120
180
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 C_T as described above. The internal pass transistor is driven on during the charging
of C_T. 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, R_CL, connected
between V_CC and CUR LIM SENS. The current-limit circuitry is activated when 0.7 V is developed across R_CL.
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.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
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Copyright © 1999, Texas Instruments Incorporated
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