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LT1683

Slew Rate Controlled Ultralow Noise Push-Pull DC/DC Controller

Linear Technology 

LT1683

TYPICAL PERFORMANCE CHARACTERISTICS

Gate Drive Undervoltage Lockout

Voltage vs Temperature

7.3

7.2 GCL = 6V

7.1

7.0

6.9

6.8

6.7

6.6

6.5

6.4

6.3

–50 –25 0 25 50 75 100 125 150

TEMPERATURE (°C)

1683 G15

Soft-Start Current vs Temperature

9.5

9.3 SS VOLTAGE = 0.9V

9.1

8.9

8.7

8.5

8.3

8.1

7.9

7.7

7.5

–50 –25 0 25 50 75 100 125 150

TEMPERATURE (°C)

1683 G16

V5 Voltage vs Load Current

5.08

5.06

T = 125°C

5.04

5.02

T = 25°C

5.00

T = –40°C

4.98

4.96

–15

–10 –5 0

5

LOAD CURRENT (mA)

10 15

1683 G17

PIN FUNCTIONS

Part Supply

V5 (Pin 5): This pin provides a 5V output that can sink or

source 10mA for use by external components. V5 source

current comes from VIN . Sink current goes to GND. VIN

must be greater than 6.5V in order for this voltage to be

in regulation. If this pin is used, a small capacitor (<1µF)

may be placed on this pin to reduce noise. This pin can

be left open if not used.

GND (Pin 11): Signal Ground. The internal error ampli-

fier, negative feedback amplifier, oscillator, slew control

circuitry, V5 regulator, current sense and the bandgap

reference are referred to this ground. Keep the connec-

tion to this pin, the feedback divider and VC compensation

network free of large ground currents.

SHDN (Pin 14): The shutdown pin can disable the switcher.

Grounding this pin will disable all internal circuitry.

Increasing SHDN voltage will initially turn on the internal

bandgap regulator. This provides a precision threshold for

the turn on of the rest of the IC. As SHDN increases past

1.39V the internal LDO regulator turns on, enabling the

control and logic circuitry.

24µA of current is sourced out of the pin above the turn on

threshold. This can be used to provide hysteresis for the

6

shutdown function. The hysteresis voltage will be set by the

Thevenin resistance of the resistor divider driving this pin

times the current sourced out. Above approximately 2.1V

the hysteresis current is removed. There is approximately

0.1V of voltage hysteresis on this pin as well.

The pin can be tied high (to VIN for instance).

VIN (Pin 17): Input Supply. All supply current for the part

comes from this pin including gate drives and V5 regula-

tor. Charge current for gate drives can produce current

pulses of hundreds of milliamperes. Bypass this pin with

a low ESR capacitor.

When VIN is below 2.55V the part will go into supply

undervoltage lockout where the gate drivers are driven low.

This, along with gate drive undervoltage lockout, prevents

unpredictable behavior during power up.

PGND (Pin 20): Power Driver Ground. This ground comes

from the MOSFET gate drivers. This pin can have several

hundred milliamperes of current on it when the external

MOSFETs are being turned off.

Oscillator

SYNC (Pin 6): The SYNC pin can be used to synchronize

the part to an external clock. The oscillator frequency

1683fd

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