LTC4441/LTC4441-1
9
44411fa
applicaTions inForMaTion
Overview
Power MOSFETs generally account for the majority of
power lost in a converter. It is important to choose not only
the type of MOSFET used, but also its gate drive circuitry.
The LTC4441/LTC4441-1 is designed to drive an N-channel
power MOSFET with little efficiency loss. The LTC4441/
LTC4441-1 can deliver up to 6A of peak current using a
combined NPN Bipolar and MOSFET output stage. This
helps to turn the power MOSFET fully “on” or “off” with
a very brief transition region.
The LTC4441/LTC4441-1 includes a programmable linear-
regulator to regulate the gate drive voltage. This regulator
provides the flexibility to use either standard threshold or
logic level MOSFETs.
DRV
CC
Regulator
An internal, P-channel low dropout linear regulator provides
the DRV
CC
supply to power the driver and the pre-driver
logic circuitry as shown in Figure 1. The regulator output
voltage can be programmed between 5V and 8V with an
external resistive divider between DRV
CC
and SGND and a
center tap connected to the FB pin. The regulator needs an
R1 value of around 330k to ensure loop stability; the value
of R2 can be varied to achieve the required DRV
CC
voltage:
R2 =
406k
DRV
CC
− 1.21V
The DRV
CC
regulator can supply up to 100mA and is
short-circuit protected. The output must be bypassed
to the PGND pin in very close proximity to the IC pins
with a minimum of 10µF ceramic, low ESR (X5R or X7R)
capacitor. Good bypassing is necessary as high transient
supply currents are required by the driver. If the input
supply voltage, V
IN
, is close to the required gate drive
voltage, this regulator can be disabled by connecting the
DRV
CC
and FB pins to V
IN
.
The LTC4441/LTC4441-1 monitors the FB pin for DRV
CC
’s
UVLO condition (UVLO in Figure 1). During power-up, the
driver output is held low until the DRV
CC
voltage reaches
90% of the programmed value. Thereafter, if the DRV
CC
voltage drops more than 20% below the programmed
value, the driver output is forced low.
Logic Input Stage
The LTC4441/LTC4441-1 driver employs TTL/CMOS com-
patible input thresholds that allow a low voltage digital
signal to drive standard power MOSFETs. The LTC4441/
LTC4441-1 contains an internal voltage regulator that
biases the input buffer, allowing the input thresholds (V
IH
= 2.4V, V
IL
= 1.4V) to be independent of the programmed-
driver supply, DRV
CC
, or the input supply, V
IN
. The 1V
hysteresis between V
IH
and V
IL
eliminates false triggering
due to noise during switching transitions. However, care
should be taken to isolate this pin from any noise pickup,
especially in high frequency, high voltage applications.The
LTC4441/LTC4441-1 input buffer has high input impedance
and draws negligible input current, simplifying the drive
circuitry required for the input. This input can withstand
voltages up to 15V above and below ground. This makes
the chip more tolerant to ringing on the input digital signal
caused by parasitic inductance.
1.09V
OUT
C
VCC
4441 F01
1.21V
UVLO
DRIVER
ENABLE
DRIVER
M
REG
FB
R2
R1
330k
–
+
V
IN
DRV
CC
PGND
REG
LTC4441
Figure 1. DRV
CC
Regulator
