1.5A DUAL HIGH-SPEED
POWER MOSFET DRIVERS
TC426
TC427
TC428
*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under "Absolute Maximum Ratings" may cause perma-
nent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions above those
indicated in the operational sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods may
effect device reliability.
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SUPPLY BYPASSING
Charging and discharging large capacitive loads quickly
requires large currents. For example, charging a 1000-pF
load to18V in 25nsec requires an 0.72A current from the
device power supply.
To guarantee low supply impedance over a wide fre-
quency range, a parallel capacitor combination is recom-
mended for supply bypassing. Low-inductance ceramic
disk capacitors with short lead lengths (< 0.5 in.) should be
used. A 1
µF
film capacitor in parallel with one or two
0.1
µF
ceramic disk capacitors normally provides adequate
bypassing.
The TC426/427/428 CMOS drivers have greatly re-
duced quiescent DC power consumption. Maximum quies-
cent current is 8 mA compared to the DS0026 40 mA
specification. For a 15V supply, power dissipation is typi-
cally 40 mW.
Two other power dissipation components are:
• Output stage AC and DC load power.
• Transition state power.
Output stage power is:
Po = P
DC
+ PAC
= Vo (I
DC
) + f C
L
V
S
Where:
Vo = DC output voltage
I
DC
= DC output load current
f
= Switching frequency
Vs = Supply voltage
In power MOSFET drive applications the P
DC
term is
negligible. MOSFET power transistors are high imped-
ance, capacitive input devices. In applications where resis-
tive loads or relays are driven, the P
DC
component will
normally dominate.
The magnitude of P
AC
is readily estimated for several
cases:
A.
1. f
2. C
L
3. Vs
4. P
AC
= 20kHZ
=1000pf
= 18V
= 65mW
B.
1. f
2. C
L
3. VS
4. P
AC
= 200kHz
=1000pf
=15V
= 45mW
GROUNDING
The TC426 and TC428 contain inverting drivers. Ground
potential drops developed in common ground impedances
from input to output will appear as negative feedback and
degrade switching speed characteristics.
Individual ground returns for the input and output
circuits or a ground plane should be used.
INPUT STAGE
The input voltage level changes the no-load or quies-
cent supply current. The N-channel MOSFET input stage
transistor drives a 2.5mA current source load. With a logic
"1" input, the maximum quiescent supply current is 8 mA.
Logic "0" input level signals reduce quiescent current to
0.4 mA maximum. Minimum power dissipation occurs for
logic "0" inputs for the TC426/427/428.
Unused driver
inputs must be connected to V
DD
or GND.
The drivers are designed with 100 mV of hysteresis.
This provides clean transitions and minimizes output stage
current spiking when changing states. Input voltage thresh-
olds are approximately 1.5V, making the device TTL com-
patible over the 4.5V to 18V supply operating range. Input
current is less than 1
µA
over this range.
The TC426/427/428 may be directly driven by the
TL494, SG1526/1527, SG1524, SE5560, and similar switch-
mode power supply integrated circuits.
POWER DISSIPATION
The supply current vs frequency and supply current vs
capacitive load characteristic curves will aid in determining
power dissipation calculations.
During output level state changes, a current surge will
flow through the series connected N and P channel output
MOSFETS as one device is turning "ON" while the other is
turning "OFF". The current spike flows only during output
transitions. The input levels should not be maintained be-
tween the logic "0" and logic "1" levels.
Unused driver
inputs must be tied to ground and not be allowed to
float.
Average power dissipation will be reduced by mini-
mizing input rise times. As shown in the characteristic
curves, average supply current is frequency dependent.
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