TC7MBL3253CFT/FK
2017-02-23
Rise and Fall Time (tr / tf) of the TC7MBL3253C I/O Signals
The tr(out) and tf(out) values of the output signals are affected by the CR time constant of the input, which consists of
the switch terminal capacitance (C
I/O
) and the on-resistance (R
ON
) of the input.
In practice, the tr(out) and tf(out) values are also affected by the circuit’s capacitance and resistance components other
than those of the TC7MBL3253C.
The tr(out) / tf(out) values can be approximated as follows. (Figure 3 shows the test circuit.)
tr(out) / tf(out) (approx) = - ( C
I/O
+ C
L
) ･ (R
DRIVE+
R
ON
) ･ ln ( ( ( V
OH
– V
OL
) – V
M
) / ( V
OH
– V
OL
) )
where, R
DRIVE
is the output impedance of the previous-stage circuit.
Calculation example:
tr(out) (approx) = - ( 13
+ 15
)E-12 ･ ( 120 + 9) ･ ln ( ( ( 3.0 - 0
) – 1.5 ) / ( 3.0 – 0
) )
≈ 2.5 ns
Calculation conditions:
V
CC
= 3.0 V, C
L
= 15 pF, R
DRIVE
= 120 Ω (output impedance of the previous IC), V
M
= 1.5 V (V
CC
/ 2)
Output of the previous IC = digital (i.e., high-level voltage = V
CC
; low-level voltage = GND)
Characteristics
V
CC
3.3 ± 0.3 V 2.5 ± 0.2 V 1.8 ± 0.15 V
V
M
V
CC
/ 2 V
CC
/ 2 V
CC
/ 2
Figure 3 Test Circuit
C
I/O
(Switch On)
R
DRIVE
= output impedance of the previous IC
R
ON
tr(out)
DRIVE
= output impedance of the previous IC
Waveform generated without the TC7MBL3253C
tf(out)
Waveform generated with the TC7MBL3253C added
