ZA3020 Datasheet, PDF (3/10 Pages) List of Unclassifed Manufacturers – 2A STEP DOWN PWM SWITCH MODE DC DC REGULATORS

ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
Figure 2: Functional Block Diagram
IN 2
SYNC 8
EN 7
Internal
Regulators
Oscillator
40/400KHz
Shutdown
Comparator
0.7V
1uA
Σ
Slope
Compensation
CLK
2.30/2.53V
Lockout
Comparato
r
Current
Sense
Amplifier
5V
Current
Comparator
SQ
RQ
1.8V
Frequency
Foldback
Comparator
0.7V
5 FB
1.22V
Error Amplifier
gm= 630uA/Volt
6 _COMP
1 BS
M1
0.2 ohm
3 SW
M2
10 ohm
4 GND
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 10ȍ switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
most of the inductor current.
ZA3020 Rev. 3.5 2003-04-22
www.vimicro.com
3