MIC2199 MICREL [Micrel Semiconductor], MIC2199 Datasheet - Page 7

• Manufacturer Part Number: MIC2199
• Manufacturer: MICREL [Micrel Semiconductor]

A ramp is added to the amplified current-sense signal to
provide slope compensation, which is required to prevent
unstable operation at duty cycles greater than 50%.
A transconductance amplifier is used for the error amplifier,
which compares an attenuated sample of the output voltage
with a reference voltage. The output of the error amplifier is
November 2004
MIC2199
C
R
COMP
COMP
COMP
1
MIC2199
RESET
PULSE-WIDTH MODULATOR
R
Q
Oscillator
COMPARATOR
CONTROL LOGIC AND
S
CORRECTIVE
PWM
Reset
Pulse
V
V
V
HSD
LSD
SW
I
RAMP
L1
V
IN
+ V
I
LOAD
V
V
V
0A
0V
0V
0V
DD
DD
0V
DD
IN
100k
Error
Amp
Figure 3. PWM-Mode Timing
Figure 2. PWM Operation
Reference
G
m
= 0.2×10
-3
7
V
V
DD
IN
the COMP (compensation) pin, which is compared to the
current-sense waveform in the PWM block. When the current
signal becomes greater than the error signal, the comparator
turns off the high-side drive. The COMP pin (pin 1) provides
access to the output of the error amplifier and allows the use
of external components to stabilize the voltage loop.
Current
Sense
Amp
A
V
= 2
CSH
4
VOUT
5
FB
3
VDD
7
VIN
6
BST
10
HSD
12
VSW
11
LSD
8
PGND
9
V
IN
V
Q2
Q1
OUT
=
0.8V
C
C
D1
D2
IN
BST
L1
⎛
⎝
1
+
R1
R2
4.7µF
R
⎞
⎠
CS
R1
R2
V
C
OUT
OUT
MIC2199
Micrel