Datasheet MIC2196 Datasheet (Micrel)

MIC2196 Micrel

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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 2Ω 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 all­ceramic 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 1µA 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.

Features

• 2.9V to 14V input voltage range

• >90% efficiency

• 2Ω output driver

• 400kHz oscillator frequency

• PWM current mode control

• 0.5µA 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

T ypical Application

V

1µF

5V

47µF

16V

IN

10nF

10k

4.7µH

MIC2196BM

VIN
EN/

UVLO
VDD

COMP

OUTN

CS

GND

FB

Si4884

(×2)

0.01Ω

B530

10k

1.15k

Adjustable Output Boost Converter

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

August 2004 1 MIC2196

V

OUT

12V, 3A

120µF
20V
(×3)

MIC2196

5V to 12V Efficiency

100

95
90
85
80
75
70
65

EFFICIENCY (%)

60
55
50

0 0.5 1 1.5 2 2.5 3 3.5 4

OUTPUT CURRENT (A)

VIN = 5V

MIC2196 Micrel

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 Configuration

FB

EN/UVLO

CS

Pin Description

Pin Number Pin Name Pin Function

1 COMP Compensation (Output): Internal error amplifier output. Connect to a

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

4 CS The (+) input to the current limit comparator. A built in offset of 100mV

5 VDD 3V internal linear-regulator output. VDD is also the supply voltage bus for the

6 GND Ground.
7 OUTN High current drive for N channel MOSFET. Voltage swing is from ground to

8 VIN Input voltage to the control IC. This pin also supplies power to the gate drive

1COMP
2
3
4

8 VIN

OUTN

7

GND

6

VDD

5

8 Lead SOIC (M)

capacitor or series RC network to compensate the regulator’s control loop.

the device, reducing the quiescent current to under 0.5µA. 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.

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.

chip. Bypass to GND with 1µF.

VIN. RON is typically 3Ω @ 5VIN.

circuit.

MIC2196 2 August 2004

MIC2196 Micrel

Absolute Maximum Ratings (Note 1)

Supply Voltage (V

Digital Supply Voltage (VDD) ...........................................7V

Comp Pin Voltage (V

Feedback Pin Voltage (VFB) .......................... –0.3V to +3V

Enable Pin Voltage (V

) .....................................................15V

IN

)............................ –0.3V to +3V

COMP

EN/UVLO

) ..................... –0.3V to 15V

Operating Ratings (Note 2)

Supply Voltage (V

Junction Temperature ....................... –40°C ≤ TJ ≤ +125°C

Package Thermal Resistance

θJA 8-lead SOIC ................................................140°C/W

) .................................... +2.9V to +14V

IN

Current Sense Voltage (VCS) ......................... –0.3V to +1V

Power Dissipation (PD) ..................... 285mW @ TA = 85°C

Ambient Storage Temperature................. –65°C to +150°C

ESD Rating, Note3 ....................................................... 2kV

Electrical Characteristics

VIN = 5V, V

Parameter Condition Min Typ Max Units
Regulation

Feedback Voltage Reference (±1%) 1.233 1.245 1.258 V

Feedback Bias Current 50 nA
Output Voltage Line Regulation 3V ≤ VIN ≤ 9V +0.08 % / V
Output Voltage Load Regulation 0mV ≤ VCS ≤ 75mV –1.2 %
Output Voltage Total Regulation 3V ≤ VIN ≤ 9V ; 0mV ≤ VCS ≤ 75mV (±3%) 1.208 1.282 V

Input & VDD Supply

VIN Input Current (IQ) (excluding external MOSFET gate current) 1 2 mA
Shutdown Quiescent Current V
Digital Supply Voltage (VDD)I
Digital Supply Load Regulation IL = 0 to 5mA 0.1 V
Undervoltage Lockout VDD 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

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 (fO) 360 400 440 kHz
Maximum Duty Cycle VFB = 1.0V 85 %
Minimum On Time VFB = 1.5V 165 ns
Frequency Foldback Threshold Measured on FB 0.3 V
Frequency Foldback Frequency 90 kHz

= 12V, TA = 25°C. Bold values indicate –40°C<TJ<+125°C; unless otherwise specified.

OUT

(±2%) 1.220 1.245 1.270 V

EN/UVLO

= 0 2.82 3.0 3.18 V

L

EN/UVLO

= 0V 0.5 5 µA

= 5V 0.2 5 µA

August 2004 3 MIC2196

MIC2196 Micrel

Parameter Condition Min Typ Max Units
Gate Drivers

Rise/Fall Time CL = 3300pF 25 ns
Output Driver Impedance Source, VIN = 12V 2 6 Ω

Sink, VIN = 12V 2 6 Ω
Source, V
Sink, VIN = 5V 3 7 Ω

= 5V 3 7 Ω

IN

Note 1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when

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, 1.5kΩ in series with 100pF.

operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction
temperature, T

, the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA.

J(Max)

MIC2196 4 August 2004

MIC2196 Micrel

y

2.8

2.85

2.9

2.95

3

3.05

0246810121416

V

DD

(V)

INPUT VOLTAGE (V)

V

DD

vs. Input Voltage

1.238

1.239

1.24

1.241

1.242

1.243

1.244

1.245

1.246

0246810121416

REFERENCE VOLTAGE (V)

INPUT VOLTAGE (V

INA

)

Reference Voltage

vs. Input Voltage

g

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

VIN = 5V

-50

0

50

100

150

200

02468101214

ENABLE PIN CURRENT (µA)

INPUT VOLTAGE (V)

Enable Pin

vs. Input Voltage

Typical Characteristics

Quiescent Current
vs. Supply Voltage

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

QUIESCENT CURRENT (mA)

0.0
02468101214

INPUT VOLTAGE (V)

3.02

3.01

3.00

2.99

2.98

(V)

2.97

DD

V

2.96

2.95

2.94

2.93

2.92
0 0.2 0.4 0.6 0.8 1.0 1.2

VDD LOAD CURRENT (mA)

Switching

VDD

vs. Load

VIN = 3.3V

VIN = 12V

Standb

VIN = 5V

Quiescent Current vs.

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

QUIESCENT CURRENT (mA)

0

-60 -40 -20 0 20 40 60 80 100120

3.5

3.4

3.3

3.2

3.1

(V)

3

DD

V

2.9

2.8

2.7

2.6

2.5

-40 -20 0 20 40 60 80 100 120

Temperature

VIN = 5V

TEMPERATURE (°C)

V

DD

vs. Temperature

VIN = 5V

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

130.0

125.0

120.0

115.0

110.0

August 2004 5 MIC2196

105.0

100.0

THRESHOLD (mV)

Reference Voltage

vs. Temperature

1.3

1.29

1.28

1.27

1.26

1.25

1.24

1.23

1.22

1.21

1.2

-40 -20 0 20 40 60 80 100 120

TEMPERATURE (°C)

Overcurrent Threshold

vs Input Voltage

95.0

90.0
02468101214

INPUT VOLTAGE (V)

VIN = 5V

Switching Frequency

vs. Input Volta

0.5

0.0

-0.5

-1.0

-1.5

-2.0

FREQUENCY VARIATION (%)

-2.5
0 2 4 6 8 10 12 14

INPUT VOLTAGE (V)

Current Limit

120
115
110
105
100

CURRENT LIMIT THRESHOLD (mV)

vs. Temperature

95
90
85
80

-40 -20 0 20 40 60 80 100 120

TEMPERATURE (°C)

e

VIN = 5V

MIC2196 Micrel

Functional Diagram

V

IN

C

IN

L1

D1

V

OUT

EN/UVLO

C

DECOUP

V

IN

8

V

3

On

Bias

REF

V

DD

COMP

Control

fs/4

Reset

Osc

Corrective

Ramp

2

100k

V

DD

5

V

DD

Overcurrent Reset

PWM
Comparator

Error

Amplifier

gm = 0.0002

Gain = 20

GND

fs/4

0.11V

Overcurrent
Comparator

Gain = 3.7

V

REF

0.3V

Frequency

Foldback

OUTN
7

CS
4

V

fb

2

R

SENSE

C

OUT

R1

R2

6GND

Figure 1. MIC2196 Block Diagram

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 N­channel MOSFETs. It features multiple frequency and duty
cycle settings. Current mode control is used to achieve
superior transient line and load regulation. An internal correc­tive ramp provides slope compensation for stable operation
above a 50% duty cycle. The controller is optimized for high­efficiency, high-performance DC-DC converter applications.
Figure 1 shows a block diagram of the MIC2196 configured

The switching cycle starts when OUTN goes high and turns
on the low-side, N-channel MOSFET, Q1. The VGS of the
MOSFET is equal to VIN. This forces current to ramp up in the
inductor. The inductor current flows through the current
sense resistor, R

. The voltage across the resistor is

SENSE

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.

as a PWM boost converter.

MIC2196 6 August 2004

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 opera­tion. 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.

PWM Mode Waveforms

Inductor Current @

Conditions:

VIN = 3V

VO = 9V

IO = 0.6A

TIME (1µs/div)

1A/div

MOSFET gate
drive @ 10V/div

Switch Mode Voltage
(MOSFET Drain)
@10V/div

VOUT Ripple Voltage
@50mV/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

V

IN

Voltage

Divider

I_inductor

Gate Driver

V

I_inductor

I_inductor

V

COMP

Gate Drive at OUTN

T

ON

T

PER

REF

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 opera­tion at duty cycles greater than 50%.

A transconductance amplifier is used as an error amplifier,
which compares an attenuated output voltage with a refer­ence 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

in Figure 1). Exceeding the

SENSE

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.

August 2004 7 MIC2196

MIC2196 Micrel

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

CRIT

2

VVV

×−

()

IN

=

O

×××

2fsLV

×

η

IN

2

O

where:

η is the efficiency of the boost converter
VIN is the minimum input voltage
L is the value of the boost inductor
FS is the switching frequency

VO is the output voltage
Maximum Peak Current in Discontinuous Mode:
The peak inductor current is:

I

IND(pk)

×× −×

=

OO

η

()

Lfs

×

IN

2I V V

where:

IO is the maximum output current
VO is the output voltage
VIN is the minimum input voltage
L is the value of the boost inductor
fS is the switching frequency
η is the efficiency of the boost converter

The maximum value of current sense resistor is:

V

R

SENSE

=

SENSE

I

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:

II

=+×

IND(pk) IND(ave) IND(pp)

VI

I

IND(pk)

OO

=

V

IN

1

2
VVV

×

+

×

I

×−×

()

L

O

×××η

2 V fs L

O

IN

η

where:

IO is the maximum output current
VO is the output voltage
VIN is the minimum input voltage
L is the value of the boost inductor
fS is the switching frequency
η is the efficiency of the boost converter
VL is the voltage across the inductor

VL may be approximated as VIN for higher input voltage.
However, the voltage drop across the inductor winding resis­tance and low-side MOSFET on-resistance must be ac­counted for at the lower input voltages that the MIC2196
operates at:

VI

×

VV

=−

LIN

OO

V

×

η

IN

RR

×+

()

WINDING DSON

where:

R

WINDING

R

DSON

is the winding resistance of the inductor

is the on resistance of the low side switching

MOSFET

The maximum value of current sense resistor is:

V

R

SENSE

=

SENSE

I

IND(pk)

where:

V

is the minimum current sense threshold

SENSE

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 switch­ing 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 2Ω 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 VDS of the MOSFET is approxi­mately equal to the output voltage. The maximum VDS 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
VGS threshold voltage of the N-channel MOSFET must be

MIC2196 8 August 2004

MIC2196 Micrel

VV 1

R1

R2

O

REF

=×+

low enough to operate at the minimum VIN voltage to guaran­tee 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 × VIN × 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.

Max. Gate Charge

250

200

150

100

50

MAXIMUM GATE CHARGE (nC)

0

02468101214

INPUT VOLTAGE (V)

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 dissipa­tion and improves efficiency. They also do not have a recov­ery 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 VDD 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 VDD voltage
for the internal supply bus. The VDD pin must be decoupled
to ground with a 1µF 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.

MIC2196

Voltage

Amplifier

V

REF

1.245V

Pin

R1

6

R2

Figure 5. Voltage Setting Components

The output voltage is determined by the equation below.

Where: V

for the MIC2196 is nominally 1.245V.

REF

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 1µF 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 capaci­tor will cause jitter and/or oscillations in the switching wave­form as well as variations in the overcurrent limit.

August 2004 9 MIC2196

MIC2196 Micrel

A minimum 1µF ceramic capacitor is required to decouple the
VIN. The capacitor should be placed near the IC and con­nected directly between pins 8 (VCC) and 6 (GND). For V
greater than 8V, use a 4.7µF or a 10µF 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

IN

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 dissipa­tion.

• 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.

MIC2196 10 August 2004

MIC2196 Micrel

Package Information

0.026 (0.65)
MAX)

PIN 1

0.157 (3.99)

0.150 (3.81)

0.050 (1.27)

0.064 (1.63)

0.045 (1.14)

TYP

0.197 (5.0)

0.189 (4.8)

DIMENSIONS:

INCHES (MM)

0.020 (0.51)

0.013 (0.33)

0.0098 (0.249)

0.0040 (0.102)

0°–8°

SEATING

PLANE

8-Pin SOIC (M)

45°

0.050 (1.27)

0.016 (0.40)

0.244 (6.20)

0.228 (5.79)

0.010 (0.25)

0.007 (0.18)

MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 [phone] FAX + 1 [phone] 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

August 2004 11 MIC2196