LT1158CN Linear Technology, LT1158CN Datasheet - Page 11

• Manufacturer Part Number: LT1158CN
• Description: IC MOSFET DRVR 1/2BRDG NCH 16DIP
• Manufacturer: Linear Technology

Specifications of LT1158CN

• Configuration: Half Bridge
• Input Type: PWM
• Current - Peak: 500mA
• Number Of Configurations: 1
• Number Of Outputs: 2
• High Side Voltage - Max (bootstrap): 56V
• Voltage - Supply: 5 V ~ 30 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Delay Time: -

APPLICATIONS INFORMATION
Ugly Transient Issues
In PWM applications the drain current of the top MOSFET
is a square wave at the input frequency and duty cycle.
To prevent large voltage transients at the top drain, a low
ESR electrolytic capacitor must be used and returned to
the power ground. The capacitor is generally in the range
of 250μF to 5000μF and must be physically sized for
the RMS current fl owing in the drain to prevent heating
and premature failure. In addition, the LT1158 requires a
separate 10μF capacitor connected closely between pins
2 and 7.
The LT1158 top source and sense pins are internally
protected against transients below ground and above
supply. However, the gate drive pins cannot be forced
below ground. In most applications, negative transients
coupled from the source to the gate of the top MOSFET
do not cause any problems. However, in some high cur-
rent (10A and above) motor control applications, negative
transients on the top gate drive may cause early tripping
of the current limit. A small Schottky diode (BAT85) from
pin 15 to ground avoids this problem.
Switching Regulator Applications
The LT1158 is ideal as a synchronous switch driver to
improve the effi ciency of step-down (buck) switching
Figure 3. Adding Synchronous Switching to a Step-Down Switching Regulator
PWM
REF
FAULT
INPUT
LT1158
T GATE DR
B GATE DR
T SOURCE
B GATE FB
T GATE FB
SENSE
SENSE
+
–
regulators. Most step-down regulators use a high current
Schottky diode to conduct the inductor current when the
switch is off. The fractions of the oscillator period that the
switch is on (switch conducting) and off (diode conduct-
ing) are given by:
Note that for V
is on, making the diode losses more signifi cant than the
switch. The worst case for the diode is during a short cir-
cuit, when V
the short-circuit current almost continuosly.
Figure 3 shows the LT1158 used to synchronously drive a
pair of power MOSFETs in a step-down regulator applica-
tion, where the top MOSFET is the switch and the bottom
MOSFET replaces the Schottky diode. Since both conduc-
tion paths have low losses, this approach can result in very
high effi ciency—from 90% to 95% in most applications.
And for regulators under 5A, using low R
MOSFETs eliminates the need for heatsinks.
R
GS
SWITCH “ON” =
SWITC
V
IN
+
H H “OFF” =
OUT
IN
approaches zero and the diode conducts
R
> 2V
SENSE
⎛
⎝ ⎜
⎛
⎝ ⎜
V
V
OUT
V
OUT
IN
IN
+
−
, the switch is off longer than it
V
⎞
⎠ ⎟
IN
1158 F03
V
•
OUT
TOTAL PERIOD
V
OUT
⎞
⎠ ⎟
•
TOTAL PERIOD
DS(ON)
LT1158
N-channel
11
1158fb