MIC5031 Datasheet, PDF (6/8 Pages) Micrel Semiconductor – High-Speed High-Side MOSFET Driver

MIC5031
Applications Information
Power-Up Sequence
The supply voltage (V_DD) must be applied to VDD before EN
is asserted. If EN is not required for the application, an RC
network must be used to delay the voltage rise applied to EN
with respect to VDD. See Figure 1.
100µF
+4.5V to +30V
100nF
0.01µF _10k
On
Off
0.01µF
0.01µF
MIC5031
7 _VDD
FLG ¹
4 _EN
RV ¹⁴
3 _CTL
10 _CP1+
G ¹⁶
CB ¹²
0.1µF
8 _CP1–
S ¹³
11 _CP2+
9 _CP2–
RI ¹⁵
0.1µF
CS ⁶
12k*
5 _GND
DLY ²
15µF
IRF540
M
2N5822
Figure 1. Enable Application
Refer to “Typical Application” for controlling EN from open-
collector or open-drain logic. The 10k resistor and 0.01µF
capacitor connected to VDD, GND, and EN keep EN low
during power up before the open-collector or open-drain logic
becomes active.
The 10k resistor and 0.01µF capacitor can be omitted if EN
is held low by the external logic until VDD is powered.
Overcurrent Detection
Using the MOSFET manufacturer’s data and the maximum
allowable load current, determine the maximum drain-to-
source voltage drop, V_DS, that will occur across the external
MOSFET in normal operation. This will also be the reference
voltage and the overcurrent trip voltage, V_R1.
V_R1 = maximum R_DS(on) × maximum load current
Supply
Micrel
Reference Current Resistor
Resistor R2 sets the reference current. For most applica-
tions, a reference current of 100µA is suggested.
R2 = ^R1
I_R2
where:
R2 = reference current resistor (Ω)
I_R2 = reference current (A) [R2 = 12kΩ for
approximately 100µA]
Reference Voltage Resistor
The reference voltage resistor value is calculated from the
reference current and the reference voltage (overcurrent
drop voltage).
R1= ^VR1
I_R2
where:
R1 = reference voltage resistor (Ω)
V_R1 = reference voltage (V) [see above]
I_R2 = reference current (A) [see above]
Overcurrent Delay Capacitor
For lamp switching applications, the delay capacitor (C_DLY)
may be as high as several microfarads. Lamps often have an
inrush current of 10× their steady-state operating current. In
PWM applications, pay attention to the input frequency vs.
the overcurrent delay. They can conflict with each other if not
properly planned.
1.23V
Bandgap
Reference
V_R1 ^IR2 R1
RV
RI
I_{R2 R2}
1.23V
External
N-Channel VDS
MOSFET
Figure 2. Resistor Calculations
MIC5031
6
August 1999