August 2004
1
MIC2196
MIC2196
Micrel
MIC2196
400kHz SO-8 Boost Control IC
Final Information
General Description
Micrel's MIC2196 is a high efficiency PWM boost control IC
housed in a SO-8 package. The MIC2196 is optimized for low
input voltage applications. With its wide input voltage range
of 2.9V to 14V, the MIC2196 can be used to efficiently boost
voltages in 3.3V, 5V, and 12V systems, as well as 1- or 2-cell
Li Ion battery powered applications. Its powerful 2
output
driver allows the MIC2196 to drive large external MOSFETs.
The MIC2196 is ideal for space-sensitive applications. The
device is housed in the space-saving SO-8 package, whose
low pin-count minimizes external components. Its 400kHz
PWM operation allows a small inductor and small output
capacitors to be used. The MIC2196 can implement all-
ceramic capacitor solutions.
Efficiencies over 90% are achievable over a wide range of
load conditions with the MIC2196's PWM boost control
scheme. Its fixed frequency PWM architecture also makes
the MIC2196 is ideal for noise-sensitive telecommunications
applications.
MIC2196 features a low current shutdown mode of 1
A and
programmable undervoltage lockout.
The MIC2196 is available in an 8-pin SOIC package with a
junction temperature range from 40
C to +125
C.
Typical Application
V
IN
5V
47
F
16V
4.7
H
Si4884
(
2)
10k
10nF
1
F
B530
1.15k
120
F
20V
(
3)
10k
0.01
MIC2196BM
VIN
EN/
UVLO
OUTN
CS
COMP
VDD
GND
FB
V
OUT
12V, 3A
Adjustable Output Boost Converter
Features
2.9V to 14V input voltage range
>90% efficiency
2
output driver
400kHz oscillator frequency
PWM current mode control
0.5
A micro power shutdown
Programmable UVLO
Front edge blanking
Cycle-by-cycle current limiting
Frequency foldback short-circuit protection
8-pin SOIC package
Applications
Step-up conversion in telecom/datacom systems
SLIC power supplies
SEPIC power supplies
Low input voltage flyback and forward converters
Wireless modems
Cable modems
ADSL line cards
Base stations
1-and 2-cell Li Ion battery operated equipment
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com
50
55
60
65
70
75
80
85
90
95
100
0 0.5 1 1.5 2 2.5 3 3.5 4
EFFICIENCY (%)
OUTPUT CURRENT (A)
MIC2196
5V to 12V Efficiency
V
IN
= 5V
MIC2196
Micrel
MIC2196
2
August 2004
Pin Configuration
1
COMP
FB
EN/UVLO
CS
8
VIN
OUTN
GND
VDD
7
6
5
2
3
4
8 Lead SOIC (M)
Ordering Information
Part Number Output Voltage Frequency Junction Temp. Range
Package
Standard Pb-Free
MIC2196BM MIC2196YM Adjustable 400KHz 40
C to +125
C
8-lead SOIC
Pin Description
Pin Number
Pin Name
Pin Function
1
COMP
Compensation (Output): Internal error amplifier output. Connect to a
capacitor or series RC network to compensate the regulator's control loop.
2
FB
Feedback (Input): Regulates FB to 1.245V.
3
EN/UVLO
Enable/Undervoltage Lockout (input): A low level on this pin will power down
the device, reducing the quiescent current to under 0.5
A. This pin has two
separate thresholds, below 1.5V the output switching is disabled, and below
0.9V the device is forced into a complete micropower shutdown. The 1.5V
threshold functions as an accurate undervoltage lockout (UVLO) with 100mV
hysteresis.
4
CS
The (+) input to the current limit comparator. A built in offset of 100mV
between CS and GND in conjunction with the current sense resistor sets the
current limit threshold level. This is also the (+) input to the current amplifier.
5
VDD
3V internal linear-regulator output. VDD is also the supply voltage bus for the
chip. Bypass to GND with 1
F.
6
GND
Ground.
7
OUTN
High current drive for N channel MOSFET. Voltage swing is from ground to
VIN. R
ON
is typically 3
@ 5V
IN
.
8
VIN
Input voltage to the control IC. This pin also supplies power to the gate drive
circuit.
August 2004
3
MIC2196
MIC2196
Micrel
Electrical Characteristics
V
IN
= 5V, V
OUT
= 12V, T
A
= 25
C. Bold values indicate 40
C<T
J
<+125
C; unless otherwise specified.
Parameter
Condition
Min
Typ
Max
Units
Regulation
Feedback Voltage Reference
(
1%)
1.233
1.245
1.258
V
(
2%)
1.220
1.245
1.270
V
Feedback Bias Current
50
nA
Output Voltage Line Regulation
3V
V
IN
9V
+0.08
% / V
Output Voltage Load Regulation
0mV
V
CS
75mV
1.2
%
Output Voltage Total Regulation
3V
V
IN
9V ; 0mV
V
CS
75mV (
3%)
1.208
1.282
V
Input & V
DD
Supply
V
IN
Input Current (I
Q
)
(excluding external MOSFET gate current)
1
2
mA
Shutdown Quiescent Current
V
EN/UVLO
= 0V
0.5
5
A
Digital Supply Voltage (V
DD
)
I
L
= 0
2.82
3.0
3.18
V
Digital Supply Load Regulation
I
L
= 0 to 5mA
0.1
V
Undervoltage Lockout
V
DD
upper threshold (turn on threshold)
2.65
V
UVLO Hysteresis
100
mV
Enable/UVLO
Enable Input Threshold
0.6
0.9
1.2
V
UVLO Threshold
1.4
1.5
1.6
V
Enable Input Current
V
EN/UVLO
= 5V
0.2
5
A
Current Limit
Current Limit Threshold Voltage
(Voltage on CS to trip current limit)
90
110
130
mV
Error Amplifier
Error Amplifier Gain
20
V/V
Current Amplifier
Current Amplifier Gain
3.7
V/V
Oscillator Section
Oscillator Frequency (f
O
)
360
400
440
kHz
Maximum Duty Cycle
V
FB
= 1.0V
85
%
Minimum On Time
V
FB
= 1.5V
165
ns
Frequency Foldback Threshold
Measured on FB
0.3
V
Frequency Foldback Frequency
90
kHz
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) ..................................................... 15V
Digital Supply Voltage (V
DD
) ........................................... 7V
Comp Pin Voltage (V
COMP
) ............................ 0.3V to +3V
Feedback Pin Voltage (V
FB
) .......................... 0.3V to +3V
Enable Pin Voltage (V
EN/UVLO
) ..................... 0.3V to 15V
Current Sense Voltage (V
CS
) ......................... 0.3V to +1V
Power Dissipation (P
D
) ..................... 285mW @ T
A
= 85
C
Ambient Storage Temperature ................. 65
C to +150
C
ESD Rating, Note3 ....................................................... 2kV
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) .................................... +2.9V to +14V
Junction Temperature ....................... 40
C
TJ
+125
C
Package Thermal Resistance
JA
8-lead SOIC ................................................ 140
C/W
MIC2196
Micrel
MIC2196
4
August 2004
Parameter
Condition
Min
Typ
Max
Units
Gate Drivers
Rise/Fall Time
C
L
= 3300pF
25
ns
Output Driver Impedance
Source, V
IN
= 12V
2
6
Sink, V
IN
= 12V
2
6
Source, V
IN
= 5V
3
7
Sink, V
IN
= 5V
3
7
Note 1.
Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when
operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction
temperature, T
J(Max)
, the junction-to-ambient thermal resistance,
JA
, and the ambient temperature, T
A
.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive, handling precautions required. Human body model, 1.5k
in series with 100pF.
August 2004
5
MIC2196
MIC2196
Micrel
Typical Characteristics
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
2
4
6
8
10 12 14
QUIESCENT CURRENT (mA)
INPUT VOLTAGE (V)
Quiescent Current
vs. Supply Voltage
Switching
Standby
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-60 -40 -20 0 20 40 60 80 100120
QUIESCENT CURRENT (mA)
TEMPERATURE (
C)
Quiescent Current vs.
Temperature
V
IN
= 5V
2.8
2.85
2.9
2.95
3
3.05
0
2
4
6
8
10 12 14 16
V
DD
(V)
INPUT VOLTAGE (V)
V
DD
vs. Input Voltage
2.92
2.93
2.94
2.95
2.96
2.97
2.98
2.99
3.00
3.01
3.02
0
0.2
0.4
0.6
0.8
1.0
1.2
V
DD
(V)
V
DD
LOAD CURRENT (mA)
VDD
vs. Load
V
IN
= 5V
V
IN
= 3.3V
V
IN
= 12V
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
3.3
3.4
3.5
-40 -20 0
20 40 60 80 100 120
V
DD
(V)
TEMPERATURE (
C)
V
DD
vs. Temperature
V
IN
= 5V
1.238
1.239
1.24
1.241
1.242
1.243
1.244
1.245
1.246
0
2
4
6
8
10 12 14 16
REFERENCE VOLTAGE (V)
INPUT VOLTAGE (V
INA
)
Reference Voltage
vs. Input Voltage
1.2
1.21
1.22
1.23
1.24
1.25
1.26
1.27
1.28
1.29
1.3
-40 -20 0
20 40 60 80 100 120
REFERENCE VOLTAGE (V)
TEMPERATURE (
C)
Reference Voltage
vs. Temperature
V
IN
= 5V
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
0
2
4
6
8
10 12 14
FREQUENCY VARIATION (%)
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
350
360
370
380
390
400
410
420
430
440
450
-40 -20 0
20 40 60 80 100 120
FREQUENCY (kHz)
TEMPERATURE (
C)
Frequency
vs. Temperature
V
IN
= 5V
90.0
95.0
100.0
105.0
110.0
115.0
120.0
125.0
130.0
0
2
4
6
8
10 12 14
THRESHOLD (mV)
INPUT VOLTAGE (V)
Overcurrent Threshold
vs Input Voltage
80
85
90
95
100
105
110
115
120
-40 -20 0
20 40 60 80 100 120
CURRENT LIMIT THRESHOLD (mV)
TEMPERATURE (
C)
Current Limit
vs. Temperature
V
IN
= 5V
-50
0
50
100
150
200
0
2
4
6
8
10 12 14
ENABLE PIN CURRENT (
A)
INPUT VOLTAGE (V)
Enable Pin
vs. Input Voltage
MIC2196
Micrel
MIC2196
6
August 2004
Functional Description
The MIC2196 is a BiCMOS, switched-mode multi-topology
controller. It will operate most low-side drive topologies
including boost, SEPIC, flyback and forward. The controller
has a low impedance driver capable of switching large N-
channel MOSFETs. It features multiple frequency and duty
cycle settings. Current mode control is used to achieve
superior transient line and load regulation. An internal correc-
tive ramp provides slope compensation for stable operation
above a 50% duty cycle. The controller is optimized for high-
efficiency, high-performance DC-DC converter applications.
Figure 1 shows a block diagram of the MIC2196 configured
as a PWM boost converter.
Functional Diagram
Osc
Error
Amplifier
0.11V
D1
L1
C
IN
fs/4
V
IN
Control
Bias
PWM
Comparator
V
REF
V
DD
GND
Overcurrent
Comparator
Frequency
Foldback
fs/4
Reset
Overcurrent Reset
Corrective
Ramp
On
Gain = 3.7
CS
4
OUTN
7
V
IN
8
V
fb
6
GND
2
V
DD
5
COMP
2
EN/UVLO
3
gm = 0.0002
Gain = 20
0.3V
100k
R2
R1
R
SENSE
C
OUT
V
OUT
V
REF
C
DECOUP
V
DD
Figure 1. MIC2196 Block Diagram
The switching cycle starts when OUTN goes high and turns
on the low-side, N-channel MOSFET, Q1. The V
GS
of the
MOSFET is equal to V
IN
. This forces current to ramp up in the
inductor. The inductor current flows through the current
sense resistor, R
SENSE
. The voltage across the resistor is
amplified and combined with an internal ramp for stability.
This signal is compared with the error voltage signal from the
error amplifier. When the current signal equals the error
voltage signal, the low-side MOSFET is turned off. The
inductor current then flows through the diode, D1, to the
output. The MOSFET remains off until the beginning of the
next switching cycle.
August 2004
7
MIC2196
MIC2196
Micrel
The description of the MIC2196 controller is broken down into
several functions:
Control Loop
PWM Operation
Current Limit
MOSFET gate drive
Reference, enable & UVLO
Oscillator
Control Loop
The MIC2196 operates in PWM (pulse-width modulated)
mode.
PWM Operation
Figure 2 shows typical waveforms for PWM mode of opera-
tion. The gate drive signal turns on the external MOSFET
which allows the inductor current to ramp up. When the
MOSFET turns off, the inductor forces the MOSFET drain
voltage to rise until the boost diode turns on and the voltage
is clamped at approximately the output voltage.
Conditions:
V
IN
= 3V
V
O
= 9V
I
O
= 0.6A
MOSFET gate
drive @ 10V/div
Switch Mode Voltage
(MOSFET Drain)
@10V/div
VOUT Ripple Voltage
@50mV/div
Inductor Current @
1A/div
PWM Mode Waveforms
TIME (1
s/div)
Figure 2. PWM Mode Waveforms
The MIC2196 uses current mode control to improve output
regulation and simplify compensation of the control loop.
Current mode control senses both the output voltage (outer
loop) and the inductor current (inner loop). It uses the inductor
current and output voltage to determine the duty cycle (D) of
the buck converter. Sampling the inductor current effectively
removes the inductor from the control loop, which simplifies
compensation. A simplified current mode control diagram is
shown in Figure 3.
I_inductor
T
ON
T
PER
V
COMP
I_inductor
I_inductor
Gate Driver
I_inductor
Voltage
Divider
V
REF
V
IN
Gate Drive at OUTN
Figure 3: PWM Control Loop
A block diagram of the MIC2196 PWM current mode control
loop is shown in Figure 1. The inductor current is sensed by
measuring the voltage across a resistor, R
SENSE
. The current
sense amplifier buffers and amplifies this signal. A ramp is
added to this signal to provide slope compensation, which is
required in current mode control to prevent unstable opera-
tion at duty cycles greater than 50%.
A transconductance amplifier is used as an error amplifier,
which compares an attenuated output voltage with a refer-
ence voltage. The output of the error amplifier is compared to
the current sense waveform in the PWM block. When the
current signal rises above the error voltage, the comparator
turns off the low-side drive. The error signal is brought out to
the COMP pin (pin 1) to provide access to the output of the
error amplifier. This allows the use of external components to
stabilize the voltage loop.
Current Sensing and Overcurrent Protection
The inductor current is sensed during the switch on time by
a current sense resistor located between the source of the
MOSFET and ground (R
SENSE
in Figure 1). Exceeding the
current limit threshold will immediately terminate the gate
drive of the N-channel MOSFET, Q1. This forces the Q1 to
operate at a reduced duty cycle, which lowers the output
voltage. In a boost converter, the overcurrent limit will not
protect the power supply or load during a severe
overcurrent condition or short circuit condition. If the
output is short-circuited to ground, current will flow from the
input, through the inductor and output diode to ground. Only
the impedance of the source and components limits the
current.
MIC2196
Micrel
MIC2196
8
August 2004
The mode of operation (continuous or discontinuous), the
minimum input voltage, maximum output power and the
minimum value of the current limit threshold determine the
value of the current sense resistor. Discontinuous mode is
where all the energy in the inductor is delivered to the output
at each switching cycle. Continuous mode of operation
occurs when current always flows in the inductor, during both
the low-side MOSFET on and off times. The equations below
will help to determine the current sense resistor value for
each operating mode.
The critical value of output current in a boost converter is
calculated below. The operating mode is discontinuous if the
output current is below this value and is continuous if above
this value.
I
V
V
V
2
fs L
V
CRIT
IN
2
O
IN
O
2
=
-
(
)
where:
is the efficiency of the boost converter
V
IN
is the minimum input voltage
L is the value of the boost inductor
F
S
is the switching frequency
V
O
is the output voltage
Maximum Peak Current in Discontinuous Mode:
The peak inductor current is:
I
2 I
V
V
L
fs
IND(pk)
O
O
IN
=
-
(
)
where:
I
O
is the maximum output current
V
O
is the output voltage
V
IN
is the minimum input voltage
L is the value of the boost inductor
f
S
is the switching frequency
is the efficiency of the boost converter
The maximum value of current sense resistor is:
R
V
I
SENSE
SENSE
IND(pk)
=
where:
V
is the minimum current sense threshold of the
CS pin.
Maximum Peak Current in Continuous Mode:
The peak inductor current is equal to the average inductor
current plus one half of the peak to peak inductor current.
The peak inductor current is:
I
I
1
2
I
I
V
I
V
V
V
V
2
V
fs L
IND(pk)
IND(ave)
IND(pp)
IND(pk)
O
O
IN
L
O
IN
O
=
+
=
+
-
(
)
where:
I
O
is the maximum output current
V
O
is the output voltage
V
IN
is the minimum input voltage
L is the value of the boost inductor
f
S
is the switching frequency
is the efficiency of the boost converter
V
L
is the voltage across the inductor
V
L
may be approximated as V
IN
for higher input voltage.
However, the voltage drop across the inductor winding resis-
tance and low-side MOSFET on-resistance must be ac-
counted for at the lower input voltages that the MIC2196
operates at:
V
V
V
I
V
R
R
L
IN
O
O
IN
WINDING
DSON
=
-
+
(
)
where:
R
WINDING
is the winding resistance of the inductor
R
DSON
is the on resistance of the low side switching
MOSFET
The maximum value of current sense resistor is:
R
V
I
SENSE
SENSE
IND(pk)
=
where:
V
SENSE
is the minimum current sense threshold
of the CS pin.
The current sense pin, CS, is noise sensitive due to the low
signal level. The current sense voltage measurement is
referenced to the signal ground pin of the MIC2196. The
current sense resistor ground should be located close to the
IC ground. Make sure there are no high currents flowing in this
trace. The PCB trace between the high side of the current
sense resistor and the CS pin should also be short and routed
close to the ground connection. The input to the internal
current sense amplifier has a 30ns dead time at the beginning
of each switching cycle. This dead time prevents leading
edge current spikes from prematurely terminating the switch-
ing cycle. A small RC filter between the current sense pin and
current sense resistor may help to attenuate larger switching
spikes or high frequency switching noise. Adding the filter
slows down the current sense signal, which has the effect of
slightly raising the overcurrent limit threshold.
MOSFET Gate Drive
The MIC2196 converter drives a low-side N-channel MOSFET.
The driver for the OUTN pin has a 2
typical source and sink
impedance. The VIN pin is the supply pin for the gate drive
circuit. The maximum supply voltage to the VIN pin is 14V.
MOSFET Selection
In a boost converter, the V
DS
of the MOSFET is approxi-
mately equal to the output voltage. The maximum V
DS
rating
of the MOSFET must be high enough to allow for ringing and
spikes in addition to the output voltage.
The VIN pin supplies the N-channel gate drive voltage. The
V
GS
threshold voltage of the N-channel MOSFET must be
August 2004
9
MIC2196
MIC2196
Micrel
low enough to operate at the minimum V
IN
voltage to guaran-
tee the boost converter will start up.
The maximum amout of MOSFET gate charge that can be
driven is limited by the power dissipation in the MIC2196. The
power dissipated by the gate drive circuitry is calculated
below:
P_gate_drive = Q_gate
V
IN
f
S
where:
Q_gate is the total gate charge of the external
MOSFET
The graph in Figure 4 shows the total gate charge which can
be driven by the MIC2196 over the input voltage range.
Higher gate charge will slow down the turn-on and turn-off
times of the MOSFET, which increases switching losses.
0
50
100
150
200
250
0
2
4
6
8
10 12 14
MAXIMUM GATE CHARGE (nC)
INPUT VOLTAGE (V)
Max. Gate Charge
Figure 4. MIC2196 Frequency vs. Gate Charge
External Schottky Diode
In a boost converter topology, the boost diode, D1 must be
rated to handle the peak and average current. The average
current through the diode is equal to the average output
current of the boost converter. The peak current is calculated
in the current limit section of this specification.
For the MIC2196, Schottky diodes are recommended when
they can be used. They have a lower forward voltage drop
than ultra-fast rectifier diodes, which lowers power dissipa-
tion and improves efficiency. They also do not have a recov-
ery time mechanism, which results in less ringing and noise
when the diode turns off. If the output voltage of the circuit
prevents the use of a Schottky diode, then only ultra-fast
recovery diodes should be used. Slower diodes will dissipate
more power in both the MOSFET and the diode. The will also
cause excessive ringing and noise when the diode turns off.
Reference, Enable and UVLO Circuits
The output drivers are enabled when the following conditions
are satisfied:
The V
DD
voltage (pin 5) is greater than its
undervoltage threshold.
The voltage on the enable pin is greater than the
enable UVLO threshold.
The internal bias circuitry generates a 1.245V bandgap
reference for the voltage error amplifier and a 3V V
DD
voltage
for the internal supply bus. The VDD pin must be decoupled
to ground with a 1
F ceramic capacitor.
The enable pin (pin 3) has two threshold levels, allowing the
MIC2196 to shut down in a micro-current mode, or turn-off
output switching in standby mode. Below 0.9V, the device is
forced into a micro power shutdown. If the enable pin is
between 0.9V and 1.5V the output gate drive is disabled but
the internal circuitry is powered on and the soft start pin
voltage is forced low. There is typically 135mV of hysteresis
below the 1.5V threshold to insure the part does not oscillate
on and off due to ripple voltage on the input. Raising the
enable voltage above the UVLO threshold of 1.5V enables
the output drivers and allows the soft start capacitor to
charge. The enable pin may be pulled up to VINA.
Oscillator and Sync
The internal oscillator is self-contained and requires no
external components. The maximum duty cycle of the MIC2196
is 85%.
Minimum duty cycle becomes important in a boost converter
as the input voltage approaches the output voltage. At lower
duty cycles, the input voltage can be closer to the output
voltage without the output rising out of regulation. Minimum
duty cycle is typically 7%.
A frequency foldback mode is enabled if the voltage on the
feedback pin (pin 2) is less than 0.3V. In frequency foldback
the oscillator frequency is reduced by approximately a factor
of 4.
Voltage Setting Components
The MIC2196 requires two resistors to set the output voltage
as shown in Figure 5.
Pin
6
Voltage
Amplifier
V
REF
1.245V
MIC2196
R1
R2
Figure 5. Voltage Setting Components
The output voltage is determined by the equation below.
V
V
1
R1
R2
O
REF
=
+
Where: V
REF
for the MIC2196 is nominally 1.245V.
Lower values of resistance are preferred to prevent noise
from apprearing on the VFB pin. A typically recommended
value for R1 is 10K.
Decoupling Capacitor Selection
A 1
F decoupling capacitor is used to stabilize the internal
regulator and minimize noise on the VDD pin. Placement of
this capacitor is critical to the proper operation of the MIC2196.
It must be next to the VDD and signal ground pins and routed
with wide etch. The capacitor should be a good quality
ceramic. Incorrect placement of the VDD decoupling capaci-
tor will cause jitter and/or oscillations in the switching wave-
form as well as variations in the overcurrent limit.
MIC2196
Micrel
MIC2196
10
August 2004
A minimum 1
F ceramic capacitor is required to decouple the
V
IN
. The capacitor should be placed near the IC and con-
nected directly between pins 8 (VCC) and 6 (GND). For V
IN
greater than 8V, use a 4.7
F or a 10
F ceramic capacitor to
decouple the VDD pin.
Efficiency Calculation and Considerations
Efficiency is the ratio of output power to input power. The
difference is dissipated as heat in the boost converter. The
significant contributors at light output loads are:
The VIN pin supply current which includes the
current required to switch the external
MOSFETs.
Core losses in the inductor.
To maximize efficiency at light loads:
Use a low gate charge MOSFET or use the
smallest MOSFET, which is still adequate for the
maximum output current.
Use a ferrite material for the inductor core, which
has less core loss than an MPP or iron power
core.
The significant contributors to power loss at higher output
loads are (in approximate order of magnitude):
Resistive on-time losses in the MOSFET
Switching transition losses in the MOSFET
Inductor resistive losses
Current sense resistor losses
Output capacitor resistive losses (due to the
capacitor's ESR)
To minimize power loss under heavy loads:
Use logic level, low on resistance MOSFETs.
Multiplying the gate charge by the on-resistance
gives a figure of merit, providing a good balance
between switching and resistive power dissipa-
tion.
Slow transition times and oscillations on the
voltage and current waveforms dissipate more
power during the turn-on and turn-off of the low
side MOSFET. A clean layout will minimize
parasitic inductance and capacitance in the gate
drive and high current paths. This will allow the
fastest transition times and waveforms without
oscillations. Low gate charge MOSFETs will
switch faster than those with higher gate charge
specifications.
For the same size inductor, a lower value will
have fewer turns and therefore, lower winding
resistance. However, using too small of a value
will increase the inductor current and therefore
require more output capacitors to filter the output
ripple.
Lowering the current sense resistor value will
decrease the power dissipated in the resistor.
However, it will also increase the overcurrent
limit and may require larger MOSFETs and
inductor components to handle the higher
currents.
Use low ESR output capacitors to minimize the
power dissipated in the capacitor's ESR.
August 2004
11
MIC2196
MIC2196
Micrel
Package Information
45
0
8
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8)
SEATING
PLANE
0.026 (0.65)
MAX
)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Pin SOIC (M)
MICREL INC.
1849 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 474-1000
WEB
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
2004 Micrel Incorporated
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