LT1158CS View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1158CS' PDF : 20 Pages View PDF
TEST CIRCUIT
LT1158
+
V+
+
V4
V6
+
10µF
50Ω
150Ω
2W
1
BOOST DR
16
BOOST
2 V+
0.01µF
3
BIAS
15
T GATE DR
14
T GATE FB
4
ENABLE
3k
1/2W
5
FAULT
6
INPUT
13
T SOURCE
LT1158 SENSE+ 12
SENSE– 11
7
GND
V+ 10
8
B GATE FB
9
B GATE DR
+
100Ω
3000pF
+
V8
+
1µF
VN2222LL
+
V16
3000pF
V14 – V13
+
V11
2k
1/2W
CLOSED
LOOP
+
V12
LT1158 TC01
U
OPERATIO (Refer to Functional Diagram)
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.
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 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 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
7
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