Datasheet
TC1426/TC1427/TC1428
DS21393D-page 6 2001-2012 Microchip Technology Inc.
3.0 APPLICATIONS INFORMATION
3.1 SUPPLY BYPASSING
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 F film capacitor in parallel with
one or two 0.1 F ceramic MLC capacitors normally
provides adequate bypassing.
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.
FIGURE 3-1: Inverting Driver Switching
Time
3.3 INPUT STAGE
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 A 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 A 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.
FIGURE 3-2: Noninverting Driver
Switching Time
+5V
10%
90%
10%
90%
10%
90%
V
DD
1 μF
WIMA
MKS-2
0V
0V
TC1426
(1/2 TC1428)
1
2
Test Circuit
0.1 μF MLC
Input
V
DD
= 16V
Output
t
R
C
L
= 1000 pF
t
D1
t
F
t
D2
Input
Output
V
DD
0.1 μF MLC
Input
V
DD
= 16V
Output
t
R
C
L
= 1000 pF
t
D1
t
F
t
D2
Input
Output
90%
10%
10%
10%
90%
1 μF
WIMA
MKS-2
TC1427
(1/2 TC1428)
+5V
0V
0V
90%
Test Circuit
1
2