MC44604_05 ONSEMI [ON Semiconductor], MC44604_05 Datasheet - Page 14

• Manufacturer Part Number: MC44604_05
• Description: High Safety Pulsed Mode Standby GreenLine TM PWM Controller
• Manufacturer: ONSEMI [ON Semiconductor]

Error Amplifier
inverting input and output is provided. It features a typical
DC voltage gain of 70 dB. The non−inverting 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.
loop compensation. The output voltage is offset by two
diodes 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 Source Output (Pin 3) when Pin 13 is at its lowest state
(V
the load is removed, or at the beginning of a soft−start
interval. The Error Amp minimum feedback resistance is
limited by the amplifier’s minimum source current (0.2 mA)
and the required output voltage (V
sense comparator’s 1.0 V clamp level:
is drawn from the pin 12 that is connected to the pin 15 in
normal mode (Note 1). Using a resistor connected on pin 12,
this current generates a voltage that is the input signal of the
error amplifier arrangement.
Note 1. The error amplifier is not used in the standby mode
R
C
Compensation
R
FB
A fully compensated Error Amplifier with access to the
The Error Amp Output (Pin 13) is provided for external
In a preferred embodiment, the feedback signal (current)
OL
1
1
). This occurs when the power supply is operating and
Feedback
Foldback
Voltage
regulation.
Figure 28. Error Amplifier Compensation
R
Input
Input
R
Pin 12
f
f (min)
13
14
2.5 V
5
+
[
R
3 · 0(1 · 0 V) ) 1· 4 V
2
Amplifier
Error
0 · 2 mA
4.7 W
MC44604
+
1.0 mA
OH
) to reach the current
2R
+ 22 kΩ
R
GND
1.0 V
4
Comparator
Current
Sense
http://onsemi.com
MC44604
14
(from Oscillator)
Current Sense Comparator and PWM Latch
and/or as a voltage mode controller. In current mode
operation, the MC44604 uses the current sense comparator,
where the output switch conduction is initiated by the
oscillator and terminated when the peak inductor current
reaches the threshold level established by the Error
Amplifier output (Pin 13). Thus the error signal controls the
peak inductor current on a cycle−by−cycle basis. The
Current Sense Comparator PWM Latch configuration used
ensures that only a single pulse appears at the Source Output
during the appropriate oscillator cycle.
the ground referenced sense resistor R
power switch Q1.
Sense Input (Pin 7) and compared to a level derived from the
Error Amp output. The peak inductor current under normal
operating conditions is controlled by the voltage at Pin 13
where:
clamped to 1.0 V. Therefore the maximum peak switch
current is:
Oscillator
V
Protection
demag out
The MC44604 can operate as a current mode controller
The inductor current is converted to a voltage by inserting
In normal mode, this voltage is monitored by the Current
The Current Sense Comparator threshold is internally
The oscillator is a very accurate sawtooth generator.
Thermal
V
OSC
V
Current Sense
OSCPROT
Comparator
Figure 29. Output Totem Pole
I
S
pk
R
R
UVLO
I
[
pk(max)
Q
V
PWM
Latch
(pin13)
Substrate
[
3 R
1· 0 V
* 1· 4 V
S
R
S
Current
Sense
V
14
7
3
C
S
in series with the
R
C
2
R
R
3
R
V
S
in
Q1