TC78B002FNG
2013-10-17
14
4. OSC Frequency and PWM Frequency
Oscillation frequency is approximated by below formula.
f
OSC
= 1/(2C[F]
×
R
OSC
[
Ω
]) [Hz]= 1/(2
×
2.08e-12[F]
×
R
OSC
[
Ω
]) [Hz]
Oscillation frequency f
OSC
is 10MHz(typ) when external resistor ROSC is 24k
Ω
PWM frequency f
PWM
=f
OSC
/400.
5. PWM Output Drive
In PWM drive, upper power transistor is turned on and off repeatedly.
In switching phase, power transistor operates in below order.
6. Startup Sequence
Output starts when VSP pin at the voltage of V
AD(L)
or more. In order to ensure the starting torque, PWM
output is 50% duty when the motor rotating speed is lower than 5Hz (typ).
When output phase is switched during startup sequence, PWM OFF term of 1ms (typ) is inserted to reduce the
regenerating current to the power supply.
VM
RF
M
RS
VM
RF
M
RS
VM
RF
M
RS
PWM ON
PWM ON
→
OFF
PWM ON
VM
RF
M
RS
VM
RF
M
RS
VM
RF
M
RS
VM
RF
M
RS
VM
RF
M
RS
PWM ON
PWM OFF
PWM OFF
PWM ON
Short brake
200ns (Design target value)
0.55V
VSP
HP
HM
OFF
（
Hi-Z)
OFF
（
Hi-Z)
OUT1
OUT2
f<5Hz
f>5Hz
50%
Duty
出力
1ms
VSP
電圧による
Duty
を出力
50% duty output
Duty is output by VSP voltage
