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LT1910E

Protected High Side MOSFET Driver

Linear Technology 

LT1910

Applications Information

Low Voltage/Wide Supply Range Operation

When the supply is less than 12V, the LT1910’s charge

pump does not produce sufficient gate voltage to fully

enhance the standard N-channel MOSFET. For these ap-

plications, a logic-level MOSFET can be used to extend

the operating supply down to 8V. If the MOSFET has a

maximum VGS rating of 15V or greater, then the LT1910

can also operate up to a supply voltage of 60V (absolute

maximum rating of the V+ pin).

Protecting Against Supply Transients

The LT1910 is 100% tested and guaranteed to be safe

from damage with 60V applied between the V+ and GND

pins. However, when this voltage is exceeded, even for a

few microseconds, the result can be catastrophic. For this

reason it is imperative that the LT1910 is not exposed to

supply transients above 60V. A transient suppressor, such

as Diodes Inc.’s SMAJ48A, should be added between the

V+ and GND pins for such applications.

For proper current sense operation, the V+ pin is required

to be connected to the positive side of the drain-sense

resistor (see Drain-Sense Configuration). Therefore, the

supply should be adequately decoupled at the node where

the V+ pin and drain sense resistor meet. Several hundred

microfarads may be required when operating with a high

current switch.

When the operating voltage approaches the 60V absolute

maximum rating of the LT1910, local supply decoupling

between the V+ and GND pins is highly recommended. An

RC snubber with a transient suppressor are an absolute

necessity. Note however that resistance should not be

added in series with the V+ pin because it will cause an

error in the current-sense threshold.

Low Side Driving

Although the LT1910 is primarily targeted at high side

(grounded load) switch applications, it can also be used

for low side (supply connected load) switch applications.

Figures 8a and 8b illustrate the LT1910 driving low side

power MOSFETs. Because the LT1910 charge pump tries

to pump the gate of the N-channel MOSFET above the

supply, a clamp Zener is required to prevent the VGS (ab-

solute maximum) of the MOSFET from being exceeded.

The LT1910 gate drive is current limited for this purpose

so that no resistance is needed between the GATE pin

and Zener.

Current sensing for protecting low side drivers can be done

in several ways. In the Figure 8a circuit, the supply voltage

for the load is assumed to be within the supply operating

range of the LT1910. This allows the load to be returned

to supply through current-sense resistor, RS, providing

normal operation of the LT1910 protection circuitry.

If the load cannot be returned to supply through RS, or

the load supply voltage is higher than the LT1910 supply,

the current sense must be moved to the source of the

low side MOSFET.

Figure 8b shows an approach to source sensing. An

operational amplifier (must common mode to ground) is

used to level shift the voltage across RS up to the drain-

sense pin. This approach allows the use of a small sense

resistor which could be made from PC trace material. The

LT1910 restart timer functions the same as in the high side

switch application.

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For more information www.linear.com/LT1910

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