MIC2182YM Micrel Inc, MIC2182YM Datasheet - Page 15

• Manufacturer Part Number: MIC2182YM
• Description: IC,SMPS CONTROLLER,CURRENT-MODE,BICMOS,SOP,16PIN,PLASTIC
• Manufacturer: Micrel Inc
• Type: Step-Down (Buck)r

Specifications of MIC2182YM

• Rohs Compliant: YES
• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.25 ~ 6 V
• Current - Output: 20A
• Frequency - Switching: 300kHz
• Voltage - Input: 4.5 ~ 32 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Power - Output: 400mW
• Number Of Pwm Outputs: 1
• On/off Pin: Yes
• Adjustable Output: Yes
• Topology: Boost/Buck
• Switching Freq: 330KHz
• Operating Supply Voltage (max): 32V
• Output Current: 20mA
• Output Voltage: 1.25 to 6V
• Synchronous Pin: Yes
• Rise Time: 60ns
• Fall Time: 60ns
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 16
• Package Type: SOP N
• Duty Cycle: 86%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-1068

It is recommended that the user limits the maximum synchro-
nized frequency to 600kHz. If a higher synchronized fre-
quency is required, it may be possible and will be design
dependent. Please consult Micrel applications for assis-
tance.
Soft Start
Soft start reduces the power supply input surge current at
startup by controlling the output voltage rise time. The input
surge appears while the output capacitance is charged up. A
slower output rise time will draw a lower input surge current.
Soft start may also be used for power supply sequencing.
April 22, 2004
MIC2182
Figure 10b. SSOP Gate Charge vs. Input Voltage
• Reduced maximum duty cycle due to switching
Figure 10a. SOP Gate Charge vs. Input Voltage
transition times and constant delay times in the
controller. As the switching frequency increased,
the switching period decreases. The switching
transition times and constant delays in the
MIC2182 start to become noticeable. The effect
is to reduce the maximum duty cycle of the
controller. This will cause the minimum input to
output differential voltage (dropout voltage) to
increase.
100
100
80
60
40
20
80
60
40
20
0
0
0
0
SOP
SSOP
4
4
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
400kHz
8
8 12 16 20 24 28 32
12 16 20 24 28 32
400kHz
500kHz
300kHz
500kHz
300kHz
15
The soft-start voltage is applied directly to the PWM compara-
tor. A 5uA internal current source is used to charge up the
soft-start capacitor. The capacitor is discharged when either
the enable voltage drops below the UVLO threshold (2.5V) or
the V
The part switches at a minimum duty cycle when the soft-start
pin voltage is less than 0.4V. This maintains a charge on the
bootstrap capacitor and insures high-side gate drive voltage.
As the soft-start voltage rises above 0.4V, the duty cycle
increases from the minimum duty cycle to the operating duty
cycle. The oscillator runs at the foldback frequency of 60kHz
until the output voltage rises above 0.95V. Above 0.95V, the
switching frequency increases to 300kHz (or the sync’d
frequency), causing the output voltage to rise a greater rate.
The rise time of the output is dependent on the soft-start
capacitor, output capacitance, output voltage, and load cur-
rent. The oscilloscope photo in Figure 9 show the output
voltage and the soft-start pin voltage at startup.
Minimum Pulse Width
The MIC2182 has a specified minimum pulse width. This
minimum pulse width places a lower limit on the minimum
duty cycle of the buck converter. When the MIC2182 is
operating in forced PWM mode (pin 2 low) and when the
output current is very low or zero, there is a limit on the ratio
of V
rise above the regulated voltage level. A minimum load is
required to prevent the output from rising up. This will not
occur for output voltages greater than 3V.
Figure 11 should be used as a guide when the MIC2182 is
forced into PWM-only mode. The actual maximum input
voltage will depend on the exact external components used
(MOSFETs, inductors, etc.).
This restriction does not occur when the MIC2182 is set to
automatic mode (pin 2 connected to a capacitor) since the
converter operates in skip mode at low output current.
Figure 11. Max. Input Voltage in Forced-PWM Mode
OUT
DD
/V
voltage drops below the UVLO level (4.1V).
IN
. If this limit is exceeded, the output voltage will
35
30
25
20
15
10
0
OUTPUT VOLTAGE (V)
1
2
3
4
5
6
M9999-042204
Micrel