TC426COA713 Datasheet, PDF (6/16 Pages) Microchip Technology – 1.5A Dual High-Speed Power MOSFET Drivers

TC426/TC427/TC428
3.0 APPLICATIONS INFORMATION
3.1 Supply Bypassing
Charging and discharging large capacitive loads
quickly requires large currents. For example, charging
a 1000 pF load to 18V in 25 nsec requires an 0.72A
current from the device 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
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.
3.2 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.
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 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/TC427/TC428. 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 thresholds are approximately 1.5V, making the
device TTL compatible over the 4.5V to 18V supply
operating range. Input current is less than 1 μA over
this range.
The TC426/TC427/TC428 may be directly driven by
the TL494, SG1526/1527, SG1524, SE5560, and
similar switch-mode power supply integrated circuits.
3.4 Power Dissipation
The supply current vs frequency and supply current
vs capacitive load characteristic curves will aid in
determining power dissipation calculations.
The TC426/TC427/TC428 CMOS drivers have greatly
reduced quiescent DC power consumption. Maximum
quiescent current is 8 mA compared to the DS0026 40
mA specification. For a 15V supply, power dissipation
is typically 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_S2
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
resistive loads or relays are driven, the P_DC component
will normally dominate.
The magnitude of P_AC is readily estimated for several
cases:
A.
B.
1. f = 200 kHZ
2. C_L =1000 pf
3. Vs = 18V
4. P_AC = 65 mW
1. f = 200 kHz
2. C_L =1000 pf
3. Vs = 15V
4. P_AC = 45 mW
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 between 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 minimizing input rise times. As shown in
the characteristic curves, average supply current is
frequency dependent.
DS21415C-page 6
© 2006 Microchip Technology Inc.