MC44603ADWR2 View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'MC44603ADWR2' PDF : 22 Pages View PDF
Vref
VCT 3.6 V
VCT low 1.6 V
VCSS + 1.6 V
MC44603A
Soft−Start
Internal Clamp
External Clamp
VOSC
Output
(Pin 3)
Figure 32. Soft−Start & Dmax
OPERATING DESCRIPTION
Error Amplifier
A fully compensated Error Amplifier with access to the
inverting input and output is provided. It features a typical
DC voltage gain of 70 dB. The noninverting input is
internally biased at 2.5 V and is not pinned out. The
converter output voltage is typically divided down and
monitored by the inverting input. The maximum input bias
current with the inverting input at 2.5 V is −2.0 mA. This can
cause an output voltage error that is equal to the product of
the input bias current and the equivalent input divider source
resistance.
The Error Amp output (Pin 13) is provided for external
loop compensation. The output voltage is offset by two
diode drops (≈ 1.4 V) and divided by three before it connects
to the inverting input of the Current Sense Comparator. This
guarantees that no drive pulses appear at the Output (Pin 3)
when Pin 13 is at its lowest state (VOL). The Error Amp
minimum feedback resistance is limited by the amplifier’s
minimum source current (0.2 mA) and the required output
voltage (VOH) to reach the current sense comparator’s 1.0 V
clamp level:
Rf(min)
[
3.0 (1.0 V) ) 1.4 V
0.2 mA
+
22 kW
+
Compensation
1.0 mA
RFB
13
Rf
Cf
14 2.5 V
Voltage
Feedback
Input
5
Error
Amplifier
2R
R
Current Sense
Comparator
1.0 V
Foldback
Input
From Power Supply Output
R1
R2
GND 4
Figure 33. Error Amplifier Compensation
Current Sense Comparator and PWM Latch
The MC44603A can operate as a current mode controller
or as a voltage mode controller. In current mode operation,
the MC44603A uses the current sense comparator. The
output switch conduction is initiated by the oscillator and
terminated when the peak inductor current reaches the
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