TL497A
SWITCHING VOLTAGE REGULATORS
SLVS009D – JUNE 1976 – REVISED JULY 1999
D
D
D
D
D
D
D
D
High Efficiency . . . 60% or Greater
Output 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
D, N, OR PW PACKAGE
(TOP VIEW)
COMP INPUT
INHIBIT
FREQ CONTROL
SUBSTRATE
GND
CATHODE
ANODE
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
CC
CUR LIM SENS
BASE DRIVE
†
BASE
†
COL OUT
NC
EMIT OUT
description
The TL497A incorporates all the active functions
required in the construction of switching voltage
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
19
250
22
350
26
400
32
500
44
750
56
1000
80
1500
120
2000
180
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.
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.
Copyright
©
1999, Texas Instruments Incorporated
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
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