HA17524P Datasheet, PDF (2/18 Pages) Hitachi Semiconductor – Switching Regulator Controller

HA17524P/FP
Functional Description
Principals of HA17524 Operation
The HA17524 switching regulator circuit, using pulse width modulation (PWM), is constructed as shown
in figure 1.
Timing resistances R_T and timing capacitance C_T control the oscillation frequency. C_T is charged by a
constant current generated by R_T. Ramp signals (saw-tooth waves) at the C_T terminal generated by this
oscillator is available for reference input signal to comparator which control the pulse width.
V_REF
V_CC 15
R_T 6
C_{T 7}
(Ramp)
Ref.
Volt.
+5 V
Osc.
+5V
16
+5 V to internal circuitry
OSC Out
+5V
Q
3
Flip Flop
NOR
Q
+5V
—
Comparator
NOR
+
+5V
INV. Input 1
NON-INV. Input 2
GND 8
— Error Amp.
+
1kΩ
10
9 COMP
+
C.L.
—
4 CL(+)
5 CL(—)
Current Limiter
SHUT _10kΩ
DOWN
12 C₁
Q₁
11 E₁
13 C₂
Q₂
14 E₂
Figure 1 HA17524 Block Diagram
The reference voltage connects to the non-inverted or inverted input terminal of the error amplifier via
resistance divider (figure 2).
The output voltage from the error amplifier is compared with the ramp signal capacitance C_T (figure 1).
The comparator can provide a signal with modulated pulse width.
This signal, then, controls output transistors Q₁ and Q₂, making an open loop to stabilize output voltage.
Outputs form the error amplifier the current limiter, and the shut-down circuit are connected together at the
comparator, so that an input signal from any one of these circuits can break the output stage.
2