TC1426/TC1427/TC1428
3.0
3.1
APPLICATIONS INFORMATION
SUPPLY BYPASSING
3.3
INPUT STAGE
Large currents are required to charge and discharge
capacitive loads quickly. For example, charging a 1000
pF load to 16V in 25 nsec requires a 0.8A current from
the device's power supply.
To ensure low supply impedance over a wide frequency
range, a parallel capacitor combination is recom-
mended for supply bypassing. Low-inductance ceramic
MLC capacitors with short lead lengths (<0.5-in.)
should be used. A 1.0
μF
film capacitor in parallel with
one or two 0.1
μF
ceramic MLC capacitors normally
provides adequate bypassing.
The input voltage level changes the no-load or
quiescent supply current. The N-channel MOSFET
input stage transistor drives a 2.5 mA current source
load. With a logic ‘1’ input, the maximum quiescent
supply current is 9 mA. Logic ‘0’ input level signals
reduce quiescent current to 500
μA
maximum.
Unused
driver inputs must be connected to V
DD
or GND.
Minimum power dissipation occurs for logic ‘0’ inputs
for the TC1426/TC1427/TC1428.
The drivers are designed with 100 mV of hysteresis.
This provides clean transitions and minimizes output
stage current spiking when changing states. Input
voltage thresholds are approximately 1.5V, making a
logic ‘1’ input any voltage greater than 1.5V up to V
DD
.
Input current is less than 1
μA
over this range.
The TC1426/TC1427/TC1428 may be directly driven
by the TL494, SG1526/27, TC38C42, TC170 and
similar switch-mode power supply integrated circuits.
3.2
GROUNDING
The TC1426 and TC1428 contain inverting drivers.
Individual ground returns for the input and output
circuits or a ground plane should be used. This will
reduce negative feedback that causes degradation in
switching speed characteristics.
Test Circuit
V
DD
= 16V
1
μF
WIMA
MKS-2
Test Circuit
V
DD
= 16V
1
μF
WIMA
MKS-2
Input
1
0.1
μF
MLC
0.1
μF
MLC
Output
C
L
= 1000 pF
Input
1
Output
C
L
= 1000 pF
2
2
TC1426
(1/2 TC1428)
TC1427
(1/2 TC1428)
+5V
Input
0V
V
DD
Output
0V
10%
10%
t
D1
90%
t
F
+5V
90%
Input
0V
10%
90%
t
R
10%
90%
t
D2
V
DD
t
R
90%
Output
0V
t
D1
t
D2
90%
t
F
10%
10%
FIGURE 3-1:
Time
Inverting Driver Switching
FIGURE 3-2:
Switching Time
Noninverting Driver
DS21393C-page 6
©
2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
