LT1158CS datasheet(7/20 Pages) LINER

7 / 20 page

LT1158

(Refer to Functional Diagram)

Whenever there is an input transition on pin 6, the LT1158

follows a logical sequence to turn off one MOSFET and

turn on the other. First, turn-off is initiated, then VGS is

monitored until it has decreased below the turn-off thresh-

old, and finally the other gate is turned on. An input latch

gets reset by every low state at pin 6, but can only be set

if the top source pin has gone low, indicating that there will

be sufficient charge in the bootstrap capacitor to safely

turn on the top MOSFET.

In order to conserve power, the gate drivers only provide

turn-on current for up to 2

µs, set by internal one-shot

circuits. Each LT1158 driver can deliver 500mA for 2

µs, or

1000nC of gate charge –– more than enough to turn on

multiple MOSFETs in parallel. Once turned on, each gate is

held high by a DC gate sustaining current: the bottom gate

by a 100

µA current source, and the top gate by an on-chip

charge pump running at approximately 500kHz.

The floating supply for the top side driver is provided by

a bootstrap capacitor between the boost pin 16 and top

source pin 13. This capacitor is recharged each time pin

The LT1158 self-enables via an internal 25

µA pull-up on

the enable pin 4. When pin 4 is pulled down, much of the

input logic is disabled, reducing supply current to 2mA.

With pin 4 low, the input state is ignored and both MOSFET

gates are actively held low. With pin 4 enabled, one or the

other of the 2 MOSFETs is turned on, depending on the

state of the input pin 6: high for top side on, and low for

bottom side on. The 1.4V input threshold is regulated and

has 200mV of hysteresis.

In order to allow operation over 5V to 30V nominal supply

voltages, an internal bias generator is employed to furnish

constant bias voltages and currents. The bias generator is

decoupled at pin 3 to eliminate any effects from switching

transients.

No DC loading is allowed on pin 3.

The top and bottom gate drivers in the LT1158 each utilize

two gate connections: 1) A gate drive pin, which provides

the turn-on and turn-off currents through an optional

series gate resistor; and 2) A gate feedback pin which

connects directly to the gate to monitor the gate-to-source

voltage and supply the DC gate sustaining current.

0.01

µF

LT1158 TC01

BOOST

T GATE DR

T GATE FB

T SOURCE

SENSE+

SENSE–

V+

B GATE DR

BOOST DR

V+

BIAS

ENABLE

FAULT

INPUT

GND

B GATE FB

V+

3000pF

µF

V16

V11

V12

3000pF

Ω

1/2W

150

Ω

V14 – V13

LT1158

VN2222LL

100

Ω

µF

CLOSED

LOOP

1/2W

TEST CIRCUIT

OPERATIO

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