LTC1163 datasheet(5/8 Pages) LINER

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LTC1163/LTC1165

OPERATIO

Gate Charge Pump

Gate drive for the power MOSFET is produced by an

internal charge pump circuit which generates a gate volt-

age substantially higher than the power supply voltage.

The charge pump capacitors are included on chip and

therefore no external components are required to generate

gate drive.

Controlled Gate Rise and Fall Times

When the input is switched ON and OFF, the gate is

charged by the internal charge pump and discharged in a

controlled manner. The charge and discharge rates have

been set to minimize RFI and EMI emissions.

BLOCK DIAGRA

(One Channel)

APPLICATIO S I FOR ATIO

Logic-Level MOSFET Switches

The LTC1163/LTC1165 are designed to operate with

logic-level N-channel MOSFET switches. Although there

is some variation among manufacturers, logic-level

MOSFET switches are typically rated with VGS = 4V with

a maximum continuous VGS rating of ±10V. RDS(ON) and

maximum VDS ratings are similar to standard MOSFETs

and there is generally little price differential. Logic-level

MOSFETs are frequently designated by an “L” and are

usually available in surface mount packaging. Some

logic-level MOSFETs are rated with VGS up to ±15V and

can be used in applications which require operation over

the entire 1.8V to 6V range.

Powering Large Capacitive Loads

Electrical subsystems in portable battery-powered equip-

ment are typically bypassed with large filter capacitors to

reduce supply transients and supply induced glitching. If

not properly powered however, these capacitors may

themselves become the source of supply glitching.

For example, if a 100

µF capacitor is powered through a

switch with a slew rate of 0.1V/

µs, the current during start-

up is:

ISTART = C(∆V/∆t)

= (100

× 10–6)(1 × 105)

= 10A

Obviously, this is too much current for the regulator (or

output capacitor) to supply and the output will glitch by as

much as a few volts.

The startup current can be substantially reduced by limit-

ing the slew rate at the gate of an N-channel as shown in

Figure 1. The gate drive output of the LTC1163/LTC1165

is passed through a simple RC network, R1 and C1, which

substantially slows the slew rate of the MOSFET gate to

approximately 1.5

× 10–4V/µs. Since the MOSFET is

operating as a source follower, the slew rate at the source

is essentially the same as that at the gate, reducing the

startup current to approximately 15mA which is easily

LTC1163

LTC1165

LTC1163/65 • BD

GATE

DISCHARGE

LOGIC

CHARGE

PUMP

BIAS

GENERATOR

HIGH

FREQUENCY

OSCILLATOR

GATE

14V

INPUT

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