ISL89163 Datasheet, PDF (10/15 Pages) Intersil Corporation – High Speed, Dual Channel, 6A, Power MOSFET Driver with Enable Inputs

ISL89163, ISL89164, ISL89165
VH = 10V
Vthres = 63% × 5V
VL = .3V
High level of the logic signal into the RC
Positive going threshold for 5V logic (B option)
Low level of the logic signal into the RC
Rdel = 100Ω
Timing values
Cdel = 1nF
tdel
=
−Rdel Cdel ×
⎛
ln⎜
VL
−
Vthres
⎝ ^{VH − VL}
+
⎞
1⎟
⎠
tdel = 34.788 ns
nominal delay time for this example
(EQ. 1)
In this example, the high logic voltage is 10V, the
positive threshold is 63% of 5V and the low level logic is
0.3V. Note the the rising edge propagation delay of the
driver must be added to this value.
The minimum recommended value of C is 100pF. The
parasitic capacitance of the PCB and any attached scope
probes will introduce significant delay errors if smaller
values are used. Larger values of C will further minimize
errors.
Acceptable values of R are primarily effected by the
source resistance of the logic inputs. Generally, 100Ω
resistors or larger are usable.
Power Dissipation of the Driver
The power dissipation of the ISL89163, ISL89164,
ISL89165 is dominated by the losses associated with the
gate charge of the driven bridge FETs and the switching
frequency. The internal bias current also contributes to
the total dissipation but is usually not significant as
compared to the gate charge losses.
12
10
V_DS = 64V
8
V_DS = 40V
6
4
2
0
0 2 4 6 8 10 12 14 16 18 20 22 24
Q_g, GATE CHARGE (nC)
FIGURE 16. MOSFET GATE CHARGE vs GATE VOLTAGE
Figure 16 illustrates how the gate charge varies with
the gate voltage in a typical power MOSFET. In this
example, the total gate charge for V_gs = 10V is 21.5nC
when V_DS = 40V. This is the charge that a driver must
source to turn-on the MOSFET and must sink to
turn-off the MOSFET.
Equation 2 shows calculating the power dissipation of
the driver:
P_D
=
2
•
Q_c
•
freq
•
V_GS
•
---------------^R-----^g---^a---^t--^e----------------
R_gate + r_DS(ON)
+
I_DD(freq)
•
V_DD
(EQ. 2)
where:
freq = Switching frequency,
V_GS = V_DD bias of the ISL89163, ISL89164, ISL89165
Q_c = Gate charge for V_GS
I_DD(freq) = Bias current at the switching frequency
(see Figure 7)
r_DS(ON) = ON-resistance of the driver
R_gate = External gate resistance (if any).
Note that the gate power dissipation is proportionally
shared with the external gate resistor. Do not overlook
the power dissipated by the external gate resistor.
10
FN7707.0
October 12, 2010