Datasheet

LT1158
8
1158fb
OPERATION
TEST CIRCUIT
0.01μF
LT1158 TC01
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
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
1μF
+
V16
+
V11
+
V12
3000pF
+
V8
V6
50Ω
+
V4
3k
1/2W
150Ω
2W
V14 – V13
LT1158
VN2222LL
100Ω
10μF
CLOSED
LOOP
2k
1/2W
+
+
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 V
GS
is moni-
tored until it has decreased below the turn-off threshold,
and fi nally 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
suffi cient 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 2μs, set by internal one-shot
circuits. Each LT1158 driver can deliver 500mA for 2μs,
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 100μA current source, and the top gate by an
on-chip charge pump running at approximately 500kHz.
The fl oating 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 13
The LT1158 self-enables via an internal 25μA 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.
(Refer to Functional Diagram)