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參數(shù)資料
| 型號： | MIC2169MM |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | 500 KHZ PWM SYNCHRONOUS BUCK CONTROL IC |
| 中文描述： | 500千赫的PWM同步降壓控制IC |
| 文件頁數(shù)： | 6/14頁 |
| 文件大?。?/td> | 160K |
| 代理商： | MIC2169MM |
MIC2169
Functional Diagram
Micrel
M9999-111803
6
November 2003
Functional Description
The MIC2169 is a voltage mode, synchronous step-down
switching regulator controller designed for high power with-
out the use of an external sense resistor. It includes an
internal soft-start function which reduces the power supply
input surge current at start-up by controlling the output
voltage rise time, a PWM generator, a reference voltage, two
MOSFET drivers, and short-circuit current limiting circuitry to
form a complete 500kHz switching regulator.
Theory of Operation
The MIC2169 is a voltage mode step-down regulator. The
figure above illustrates the block diagram for the voltage
control loop. The output voltage variation due to load or line
changes will be sensed by the inverting input of the
transconductance error amplifier via the feedback resistors
R3, and R2 and compared to a reference voltage at the non-
inverting input. This will cause a small change in the DC
voltage level at the output of the error amplifier which is the
input to the PWM comparator. The other input to the com-
parator is a 0 to 1V triangular waveform. The comparator
generates a rectangular waveform whose width t
ON
is equal
to the time from the start of the clock cycle t
0
until t
1
, the time
the triangle crosses the output waveform of the error ampli-
fier. To illustrate the control loop, let us assume the output
voltage drops due to sudden load turn-on, this would cause
Current Limit
Reference
Current Limit
Comparator
Error
Amp
LDriver
High-Side
Comparator
FB
COMP
GND
LSD
V
REF
+3%
V
REF
3%
HSD
V
DD
C
BST
CS
V
DD
5V
5V
5V
C2
C1
R1
5V
0.8V
V
IN
SW
Q2
Q1
L1
Driver
Logic
0.8V
BG Valid
Clamp &
Startup
Current
Enable
Error
Loop
Comparator
5V LDO
Bandgap
Reference
Soft-Start &
Digital Delay
Counter
MIC2169
Ramp
Clock
BOOST
R2
R3
4
RSW
RCS
C
OUT
V
OUT
C
IN
D1
MIC2169 Block Diagram
the inverting input of the error amplifier which is divided down
version of V
OUT
to be slightly less than the reference voltage
causing the output voltage of the error amplifier to go high.
This will cause the PWM comparator to increase t
ON
time of
the top side MOSFET, causing the output voltage to go up
and bringing V
OUT
back in regulation.
Soft-Start
The COMP/EN pin on the MIC2169 is used for the following
three functions:
1. Disables the part by grounding this pin
2. External compensation to stabilize the voltage
control loop
3. Soft-start
For better understanding of the soft-start feature, let
’
s as-
sume V
IN
= 12V, and the MIC2169 is allowed to power-up by
un-grounding the COMP/EN pin. The COMP pin has an
internal 6.5
μ
A current source that charges the external com-
pensation capacitor. As soon as this voltage rises to 180mV
(t = Cap_COMP
×
0.18V/8.5
μ
A), the MIC2169 allows the
internal V
DD
linear regulator to power up and as soon as it
crosses the undervoltage lockout of 2.6V, the chip
’
s internal
oscillator starts switching. At this point in time, the COMP pin
current source increases to 40
μ
A and an internal 11-bit
counter starts counting which takes approximately 2ms to
complete. During counting, the COMP voltage is clamped at
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