TL497AC Datasheet, PDF (1/11 Pages) Texas Instruments – SWITCHING VOLTAGE REGULATORS

TL497AC, TL497AI, TL497AY
SWITCHING VOLTAGE REGULATORS
• 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
SLVS009C – JUNE 1976 – REVISED AUGUST 1995
TL497AC, TL497AI . . . 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 DRIVEâ€} 
11 ^BASE†
10 ^{COL OUT}
9 ^NC
8 ^{EMIT OUT}
NC – No internal connection
† _{BASE (11) and BASE DRIVE (12) are used for device testing only.}
They are not normally used in circuit applications of the device.
description
The TL497AC and TL497AI incorporate on a single monolithic chip all the active functions required in the
construction of switching voltage regulators. They can also be used as the control element to drive external
components for high-power-output applications. The TL497AC and TL497AI were designed for ease of use in
step-up, step-down, or voltage inversion applications requiring high efficiency.
The TL497AC and TL497AI are fixed-on-time variable-frequency switching-voltage-regulator control circuits.
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 may 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 is also available for
blocking or commutating purposes. The TL497AC and TL497AI also have 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.
TA
0°C to 70°C
– 40°C to 85°C
AVAILABLE OPTIONS
PACKAGED DEVICES
SURFACE MOUNT
(D)
PLASTIC DIP
(N)
SHRINK
SMALL OUTLINE
(PW)
TL497ACD
TL497ACN
TL497ACPW
TL497AID
TL497AIN
—
CHIP
FORM
(Y)
TL497AY
—
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.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
Copyright © 1995, Texas Instruments Incorporated
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