Hi
I am designing a very simple buck converter. Just to test equations that is given in application notes from various electronic manufacturers.
The MOSFET I will be using is STP14NK50Z (N Channel).
Here is the parameters for my buck converter:
Vin: 60V
Fsw: 30kHz
Vout: 48V
Iout: 10A
Before I start the design of the buck converter, I want to to calculate what driver I will be requiring.
Using the app notes from Microchip (AN799 and AN898)
Power Dissapation in Driver:
Power loss Due to charging and discharging gate cap in mosfet:
Pc = Cg * Vgs^2*Fsw
and
Cg = Qg/Vgs
From Figure 11 in the STP14NK50Z datasheet, a Vgs of 10V is chosen and the Qg is read from the datasheet: Qg = 73nC
Thus: Cg = Qg/Vgs = 73nC/10V = 7.3nF
And:
Pc = Cg * Vgs^2*Fsw = 7.3nF* 10V^2 * 30kHz = 21.9mW
Power loss Due to cross over distortion mosfet:
Ps = CC * Fsw * Vin,
where CC is read from STP14NK50Z datasheet, Table 7, "tc" typical value
thus
Ps = 20nS * 30kHz * 60V = 36mW
Calculate Current required from Gate Driver
Idriver = Qg/dT, where
Qg = 73nC
and according to the AN799 app note dT = Turn-on/turn-off time, now I dont know if they mean Turn-on OR turn-off time or Turn-on Divide by turn-off time. So i took the absolute worst case, took td(on). (Table 7)
This resulted in:
Idriver = Q/dT = 73nC / 24nS = 3A.
The current that the gate driver is suppose to supple seems quite high.. Can you guys have a look through and suggestions/comments are welcome!!
I am designing a very simple buck converter. Just to test equations that is given in application notes from various electronic manufacturers.
The MOSFET I will be using is STP14NK50Z (N Channel).
Here is the parameters for my buck converter:
Vin: 60V
Fsw: 30kHz
Vout: 48V
Iout: 10A
Before I start the design of the buck converter, I want to to calculate what driver I will be requiring.
Using the app notes from Microchip (AN799 and AN898)
Power Dissapation in Driver:
Power loss Due to charging and discharging gate cap in mosfet:
Pc = Cg * Vgs^2*Fsw
and
Cg = Qg/Vgs
From Figure 11 in the STP14NK50Z datasheet, a Vgs of 10V is chosen and the Qg is read from the datasheet: Qg = 73nC
Thus: Cg = Qg/Vgs = 73nC/10V = 7.3nF
And:
Pc = Cg * Vgs^2*Fsw = 7.3nF* 10V^2 * 30kHz = 21.9mW
Power loss Due to cross over distortion mosfet:
Ps = CC * Fsw * Vin,
where CC is read from STP14NK50Z datasheet, Table 7, "tc" typical value
thus
Ps = 20nS * 30kHz * 60V = 36mW
Calculate Current required from Gate Driver
Idriver = Qg/dT, where
Qg = 73nC
and according to the AN799 app note dT = Turn-on/turn-off time, now I dont know if they mean Turn-on OR turn-off time or Turn-on Divide by turn-off time. So i took the absolute worst case, took td(on). (Table 7)
This resulted in:
Idriver = Q/dT = 73nC / 24nS = 3A.
The current that the gate driver is suppose to supple seems quite high.. Can you guys have a look through and suggestions/comments are welcome!!
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