MIC9131BM Micrel Inc, MIC9131BM Datasheet - Page 10

• Manufacturer Part Number: MIC9131BM
• Description: IC CTRLR DC-DC PWM HV HS 16-SOIC
• Manufacturer: Micrel Inc

Specifications of MIC9131BM

• Applications: Controller, Telecom
• Voltage - Input: 9 ~ 18 V
• Number Of Outputs: 1
• Voltage - Output: 4.7 ~ 5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

MIC9131
plied and the depletion FET, which is normally enabled allows
current from V
V
the gate drive is enabled and the MIC9131 starts switching.
Vcc continues to increase until the Pre-Regulator turn-off
threshold, (V
turned off. The Vcc voltage decreases as energy from the
bias capacitor is used to supply the controller. The deple-
tion FET is turned back on when the pre-regulator turn-on
threshold is reached. A bias winding derived supply voltage,
set higher than the FET turn-off threshold, V
the V
from turning on.
In certain designs the MIC9131 may be powered directly from
the Line voltage, eliminating the need for an extra transformer
bias winding. When operating in this fashion the designer
must insure the power dissipation in the IC does not cause
the die temperature to exceed the 125°C maximum. Power
dissipation is calculated by:
Where :
I
a given frequency and the average current required to drive
the external switching MOSFET. A plot of typical operating
current vs. frequency is given in Figure 3. The average MOS-
FET gate drive current is calculated in the “MOSFET GATE
DRIVE” section of this specification.
The die junction temperature is calculated by
Where: T
When powered directly from the Line voltage, the V
age will vary between the upper and lower pre-regulator
thresholds. The amplitude of the output gate drive voltage
will vary with the V
for most topologies since the variation is small (equal to the
M9999-080206
VCC
CC
voltage reaches the V
is the sum of the operating current of the MIC9131 at
CC
V
V
I
T
T
θ
of the MIC9131 (listed in the operating ratings
section of the specification.
P
VCC
voltage over the threshold and prevents the FET
J
DISS
J
A
JA
IN
CC
=
is the die junction temperature
is the ambient temperature of the circuit
is the junction to ambient thermal resistance
is the line input voltage
T
PR
is the average V
=
is the total current drawn by the IC
A
IN
(
+
(OFF)), is reached and the depletion FET is
V
to charge the V
P
IN
DISS
10
CC
9
8
7
6
5
4
3
2
1
0
−
GATE DRIVE FREQUENCY (kHz)
V
voltage. This should not be a problem
CC
× θ
Quiescent Current
vs. Frequency
)
Figure 3
JA
×
CC
C t = 470pF
I
VCC
CC
enable threshold, V
CC
voltage (typically 8.5V)
C
bias capacitor. Once the
t
= 100pF
PR
(OFF), raises
GLO
CC
(ON) ,
volt-
10
ΔV
the internal circuits from V
The pre-regulator FET is protected by a thermal shutdown
circuit, which turns the MOSFET off if its temperature exceeds
approximately 150°C.
When operating at input voltages greater than 150V, a fast
input voltage risetime during turn-on (which may occur during
a hot plug operation)may cause a high peak current to flow
through the depletion FET, damaging the MIC9131. A 1.8kΩ
resistor in series between the input voltage and the Line pin
(pin 1) is recommended when operating at input voltages
greater than 150V. This resistor limits the maximum peak
current to 100mA (at 180V
The depletion mode MOSFET contains an internal parasitic
diode. The V
voltage or the V
greater than the V
in the parasitic diode will destroy the IC.
V
The power for the controller and gate drive circuitry is supplied
through the V
ground through the power ground pin (PGND). The rest of
the supply current is returned to ground through the analog
ground pin (AGND). The two ground pins must be connected
together through the PCB ground plane.
High frequency decoupling is provided at the V
the gate drive’s peak current requirements. Turn-on of the
external MOSFET causes a voltage glitch on the V
the glitch is excessive, this disruption can appear as noise or
jitter in the oscillator circuit or the gate drive waveform. The
decoupling capacitor must be able to supply the MOSFET
gate with the charge required to turn it on. A 0.1µF ceramic
capacitor is usually sufficient for most MOSFETs. Larger
FETs, with a higher gate charge requirement may require a
0.22µF ceramic capacitor or a ceramic capacitor paralleled
with a 2.2µF tantalum or 4.7uF aluminum electrolytic. It is
recommend that if V
maximum capacitor recommended on V
pacitor must be located next to the V
The ground end of the capacitor should be connected to the
ground plane, making a low impedance connection to the
power ground pin (pin 15).
The internal bias regulator block provides several internal and
external bias voltages. Referring to Figure 1, a 2.5V refer-
ence is used for the internal error amplifier, a 0.82V bias is
used by the current limit comparator and a 1.21V reference
is used by the Line UVLO circuit. An external 5V bias volt-
age (V
as a reference voltage for other external components. The
V
decoupling.
Enable and Undervoltage Monitoring Circuits
The two undervoltage lockout circuits in the MIC9131 are
shown in Figure 4. One monitors the V
other monitors the input line voltage. These signals are OR’d
together and either one can disable the gate drive pin and
discharge the voltage on the soft start capacitor.
CC
BIAS
PR
and Bias Supplies
hysteresis). The bias regulator in the MIC9131 buffers
pin requires a minimum 0.1µF capacitor to ground for
BIAS
) powers the oscillator circuit and may be used
CC
IN
CC
pin voltage must be greater than the V
pin. The gate drive current is returned to
IN
voltage will be clamped to a diode drop
LINE
voltage. Excessive power dissipation
is greater than 150V DC than the
CC
IN
) and protects the part.
variations.
CC
pin of the MIC9131.
CC
CC
is 2.2µF.The ca-
voltage and the
CC
August 2006
pin to supply
Micrel, Inc.
CC
pin. If
CC