LTC1174CS8 datasheet(9/16 Pages) LINER

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LTC1174

LTC1174-3.3/LTC1174-5

APPLICATI

I FOR ATIO

Figure 3. Low-Battery Comparator

LTC1174

–

1.25V

REFERENCE

VIN

1174 F03

LTC1174 Adjustable Applications

The LTC1174 develops a 1.25V reference voltage between

the feedback (pin 1) terminal and ground (see Figure 4). By

selecting resistor R1, a constant current is caused to flow

through R1 and R2 to set the overall output voltage. The

regulated output voltage is determined by:

OUT =+









125 1

For most applications, a 30k resistor is suggested for R1.

To prevent stray pickup, a 100pF capacitor is suggested

across R1 located close to the LTC1174.

Figure 4. LTC1174 Adjustable Configuration

LTC1174

VFB

VOUT

1174 F04

100pF

Inverting Applications

The LTC1174 can easily be set up for a negative output

voltage. If – 5V is desired, the LTC1174-5 is ideal for this

application as it requires the least components. Figure 5

shows the schematic for this application. Note that the

output voltage is now taken off the GND pin. Therefore,

the maximum input voltage is now determined by the

difference between the absolute maximum voltage rating

and the output voltage. A maximum of 12V is specified in

LTC1174HV-5

LBIN

LBOUT

IPGM

GND

VIN

SHUTDOWN

VOUT

µH**

VOUT

–5V

45mA

× 47µF*

16V

MBRS140T3

1174 F05

AVX TPSD476K016

COILTRONICS CTX50-4

INPUT VOLTAGE

4V TO 12V

0.1

µF

× 47µF*

16V

Figure 5. Positive-to-Negative 5V Converter

Figure 5, giving the circuit a 1.5V of headroom for VIN.

Note that the circuit can operate from a minimum of 4V,

making it ideal for a 4 NiCad cell application. For a higher

output current circuit, please refer to the Typical Applica-

tions section.

Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC1174. These items are also illustrated graphically in

the layout diagram in Figure 6. Check the following in your

layout:

1. Is the Schottky catch diode

closely connected between

ground (pin 4) and switch (pin 5)?

2. Is the “+” plate of CIN closely connected to VIN (pin 6)?

This capacitor provides the AC current to the internal

P-channel MOSFET.

3. Is the 0.1

µF VIN decoupling capacitor closely conected

between VIN (pin 6) and ground (pin 4)? This capacitor

carries the high frequency peak currents.

4. Is the SHUTDOWN (pin 8) actively pulled to VIN during

normal operation? The SHUTDOWN pin is high imped-

ance and must not be allowed to float.

5. Is the IPGM (pin 7) pulled either to VIN or ground? The

IPGM pin is high impedance and must not be allowed

to float.

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