MIC2142(2000) View Datasheet(PDF) - Micrel
Part Name
Description
Manufacturer
MIC2142 Datasheet PDF : 17 Pages
| |||
MIC2142
Functional Diagram
Bandgap
Reference
EN
Shutdown
FB
MIC2142
VCC
Oscillator
330kHz
FIXED DUTY CYCLE
Micrel
SW
GND
Functional Description
This MIC2142 is a fixed duty cycle, constant frequency, gated
oscillator, micropower, switch-mode power supply controller.
Quiescent current for the MIC2142 is only 85µA in the switch
off state, and since a MOSFET output switch is used, addi-
tional switch drive current is minimized. Efficiencies above
85% throughout most operating conditions can be realized.
A functional block diagram is shown above and typical
schematic is shown on page 1. Regulation is performed by a
hysteretic comparator, which regulates the output voltage by
gating the internal oscillator. The internal oscillator operates
at a fixed 57% duty cycle and 330kHz frequency. For the fixed
output versions, the output is divided down internally and then
compared to the internal VREF input. An external resistive
divider is use for the adjustable version.
The comparator has hysteresis built into it, which determines
the amount of low frequency ripple that will be present on the
output. Once the feedback input to the comparator exceeds
the control voltage by 18mV, the high frequency oscillator
drive is removed from the output switch. As the feedback
input to the comparator returns to the reference voltage level,
the comparator is reset and the high frequency oscillator is
again gated to the output switch. The 18mV of hysteresis
seen at the comparator will be multiplied by the ratio of the
output voltage to the reference voltage. For a five volt output
this ratio would be 4, corresponding to a ripple voltage of
72mV at the output.
The maximum output voltage is limited by the voltage capa-
bility of the output switch. Output voltages up to 22V can be
achieved with a standard boost circuit. Higher output volt-
ages can be realized with a flyback configuration.
MIC2142
6
December 2000
Share Link: 