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参数资料
| 型号： | G5180 |
| 厂商： | Global Mixed-mode Technology Inc. |
| 英文描述： | Switching Regulator Power Controller |
| 中文描述： | 开关稳压电源控制器 |
| 文件页数： | 7/9页 |
| 文件大小： | 341K |
| 代理商： | G5180 |
Ver: 0.4 Preliminary
Apr 27, 2006
TEL: 886-3-5788833
http://www.gmt.com.tw
7
G5180
Global Mixed-mode Technology Inc.
Description
Soft Start SCP
At power on, the G5180 enters the soft-start mode to
prevent current spike and overshoot. The capacitor CS
is charged from 0V with a constant current of 1A.
The soft-start time for the duty cycle
tS = 0.8 x CS (F)
When VSCP reaches 0.8V, the G5180 leaves the
soft-start mode to enter the normal mode and enable
the SCP function. If the output load conditions change
rapidly causing the output to drop suddenly, the ex-
ternal capacitor CS will start to charge because the
error amplifier output (FB pin) is fixed at VOMax
+. When
the external capacitor is charged above 0.8V, the out-
put pin is set low. Once the latch circuit has set, the
capacitor CS will be discharged to low state and the
latch circuit will not reset until power is turned off or
the power supply is restarted.
Short-circuit detection time (or full soft-start time):
tPE = 0.8 x CS (F)
Setting Oscillating Frequency
The oscillator circuit generates a triangular sawtooth
wave with a peak of 0.8V and a trough of 0.1V using
the timing capacitor (CT) and the timing resistor (RT)
that are connected to the OSC pin. This oscillator can
provide oscillating frequency in the range from 20kHz
to 1MHz. The waveform of the OSC pin is shown as
Figure 1.
Figure 1
The cycle (T) can be determined as follows:
VX
VX = VH x e
- t / (C
T
x R
T
)
t = -CT x RT x ln
(
VH
)
(
)
[ ]s
R
C
1
.
2
8
.
0
/
1
.
0
ln
R
C
T
×
≈
×
=
Switching Regulator Function
Reference Voltage circuit
A temperature-compensated reference voltage (~1.25V)
is generated by the reference voltage circuit from the
voltage supplied by the power supply pin (pin 3). The
circuit also sets the idle period besides providing the
reference voltage for the switching regulator.
Error Amplifier
The error amplifier detects the output voltage of the
switching regulator and sets the PWM control signal.
The voltage gain is fixed. The system is made stable
by connecting a phase compensation capacitor to the
FB pin (pin 8).
PWM Comparator
The voltage comparator includes one inverting and
three non-inverting inputs. The comparator is a voltage
to pulse width converter that controls the ON time of
the output pulse depending on the level of input volt-
age. The output level remains high when the sawtooth
wave is lower than the error amplifier output voltage,
the soft start setting voltage, and the idle period setting
voltage.
Output Circuit
The output circuit can drive an external NPN transistor
or NMOS directly. The value of the ON/OFF current
can be set by a resistor connected to the BR/CTL pin
(pin 4). Stand-by mode (supply current 1A or less)
can be set by connecting the BR/CTL pin (pin 4) to VCC
or by making the pin open.
Under-Voltage Lockout (UVLO)
Transients during powering on or instantaneous
glitches in the supply voltage can cause the control IC
to malfunction and damage the system. To prevent
malfunction at low input voltage, the circuit compares
the supply voltage to the internal reference voltage to
detect a low input voltage. Once detected, the circuit
sets the output pin low.
0.8V
0.1V
V
OSC
V
H
V
X
V
L
t
Time
0.8V
0.1V
V
OSC
V
H
V
X
V
L
t
Time
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