TLE2662 datasheet(32/40 Pages) TI

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TLE2662

DUAL

µPOWER JFET-INPUT OPERATIONAL AMPLIFIER

WITH SWITCHED-CAPACITOR VOLTAGE CONVERTER

SLOS118B – DECEMBER 1992 – REVISED AUGUST 1994

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

pin functions (see functional block diagram – converter)

Supply voltage (SCIN) alternately charges CIN to the input voltage when CIN is switched in parallel with the

input supply, and then transfers charge to COUT when CIN is switched in parallel with COUT. Switching

occurs at the oscillator frequency. During the time that CIN is charging, the peak supply current is

approximately 2.2 times the output current. During the time that CIN is delivering a charge to COUT, the

supply current drops to approximately 0.2 times the output current. An input supply bypass capacitor supplies

part of the peak input current drawn by the TLE2662 switched-capacitor section and averages out the current

drawn from the supply. A minimum input supply bypass capacitor of 2

µF, preferably tantalum or some other

low-ESR type, is recommended. A larger capacitor is desirable in some cases. An example is when the actual

input supply is connected to the TLE2662 through long leads or when the pulse currents drawn by the

TLE2662 might affect other circuits through supply coupling.

In addition to being the output pin, SCOUT is tied to the substrate of the device. Special care must be taken in

TLE2662 circuits to avoid making SCOUT positive with respect to any of the other pins. For circuits with the

output load connected from VCC+ to SCOUT or from some external positive supply voltage to SCOUT, an

external Schottky diode must be added (see Figure 61). This diode prevents SCOUT from being pulled above

the GND during start up. A fast-recovery diode such as IN4933 with low forward voltage (Vf ≈ 0.2 V) can be

used.

IN4933

Load

SCOUT

1OUT

1IN –

1IN +

VCC –

SCOUT

SCREF

OSC

SCIN

VCC +

2OUT

2IN –

2IN +

CAP –

GND

CAP +

FB/SD

COUT

CIN

VCC+ or External Supply Voltage

Figure 61. Circuit With Load Connected From VCC to SCOUT

The voltage reference (SCREF) output provides a 2.5-V reference point for use in TLE2662-based regulator

circuits. The temperature coefficient (TC) of the reference voltage has been adjusted so that the TC of the

regulated output voltage is near zero. As seen in the typical performance curves, this requires the reference

output to have a positive TC. This nonzero drift is necessary to offset a drift term inherent in the internal

reference divider and comparator network tied to the feedback pin. The overall result of these drift terms is a

regulated output that has a slight positive TC at output voltages below 5 V and a slight negative TC at output

voltages above 5 V. For regulator-feedback networks, reference output current should be limited to

approximately 60

µA. SCREF draws approximately 100 µA when shorted to ground and does not affect the

internal reference/regulator. This pin can also be used as a pullup for TLE2662 circuits that require

synchronization.

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