參數(shù)資料
型號: ZA3020
廠商: Electronic Theatre Controls, Inc.
英文描述: 2A STEP DOWN PWM SWITCH MODE DC DC REGULATORS
中文描述: 第2A降壓PWM開關(guān)模式DC DC穩(wěn)壓器
文件頁數(shù): 3/10頁
文件大?。?/td> 134K
代理商: ZA3020
Figure 2: Functional Block Diagram
Σ
40/400KHz
Oscillator
Slope
Compensation
1.8V
Current
Comparator
8
Internal
Regulators
2
1uA
2.30/2.53V
0.7V
7
Shutdown
Comparator
Lockout
Comparato
r
3
4
M2
10 ohm
M1
0.2 ohm
6
1.22V
5
Error Amplifier
gm= 630uA/Volt
IN
SYNC
EN
COMP
FB
GND
SW
BS
1
0.7V
Frequency
Foldback
Comparator
5V
CLK
S
R
Q
Q
Current
Sense
Amplifier
Functional Description
The
ZA3020
is a current mode r egulator. That is,
the compensation pin voltage is proportional to the
current delivered to the load.
At the beginning of a cycle: the upper transistor M1
is off; the lower transistor M2 on; the COMP pin
voltage is higher than the current sense amplifier
output; and the current comparator’s output is low.
The rising edge of the 380KHz CLK signal sets the
RS Flip-Flop. Its output turns off M2 and turns on
M1 thus connecting the Switch pin and inductor to
the Input supply. The increasing inductor current is
sensed and amplified by the Current Sense
Amplifier. Ramp compensation is summed to
Current Sense Amplifier output and compared to
the error amplifier output by the Current
Comparator. When the Current Sense Amplifier
plus Slope Compensation signal exceeds the
Comp pin voltage, the RS Flip-Flop is reset and the
chip reverts to its initial M1 off, M2 on state.
If the Current Sense Amplifier plus Slope
Compensation signal does not exceed the COMP
voltage, then the falling edge of the CLK resets the
Flip-Flop.
The output of the Error amplifier integrates the
voltage difference between the feedback and the
1.22V bandgap reference. The polarity is such that
feedback pin voltages lower than 1.22V increases
the COMP pin voltage. Since the COMP pin’s
voltage is proportional to the peak inductor current
an increase in its voltage increases current
delivered to the output.
The lower 10
switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
most of the inductor current.
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.
5
2003-04-
22
www.vimicro.com
3
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