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參數資料
| 型號： | UC3910DTR |
| 英文描述： | VERY LOW QUIESCENT CURRENT DUAL VOLTAGE REGULATOR |
| 中文描述： | D / A轉換 |
| 文件頁數： | 4/6頁 |
| 文件大小： | 247K |
| 代理商： | UC3910DTR |
pins.
OVP (Overvoltage Comparator Output):
This output
pin drives an external SCR circuit with up to 65mA
when the voltage on VSENSE rises above its nominal
value by a percentage set by the voltage on the
OVTH/UVTH pin (see below). The OVP comparator hys-
teresis is a function of both the DACBUF voltage and
the OV/UV percentage programmed.
OVPB (Overvoltage Comparator Complementary
Output):
This output is a complement to the OVP out-
put (see above) and provides an open collector capable
of sinking 1mA when the voltage on VSENSE rises
above its nominal value by a percentage set by the volt-
age on the OVTH/UVTH pin (see below).
OVTH/UVTH (Undervoltage and Lower Overvoltage
Threshold Input):
This pin is used to program the win-
dow thresholds for the OV and UV comparators. The
OV-UV window is centered around the DACBUF voltage
and can be programmed from
±
5% to
±
15% about
DACBUF. Connect a resistor divider between DACBUF
and GND to set the percentage. The threshold for the
OVP comparator is internally set to a percentage 2
times larger than the programmed OV percentage;
therefore, its range extends from 10% to 30% above
DACBUF.
PWRGOOD (Undervoltage/Lower Overvoltage Out-
put):
This pin is an open collector output which is
driven low to reset the microprocessor when VSENSE
rises above or falls below its nominal value by a per-
centage programmed by OVTH/UVTH. The OV and UV
comparators’ hysteresis is a function of the DACBUF
voltage and the OV/UV programmed percentage.
VCC (Positive Supply Voltage):
This pin supplies
power to the chip. Connect VCC to a stable voltage
source of at least 9V and capable of sourcing at least
15mA. The OVP and PWRGOOD outputs are held low,
the OVPB output is in a high impedance state, and the
VSENSE pin is pulled low until VCC exceeds the upper
undervoltage lockout threshold. This pin should be by-
passed directly to the GND pin with a 0.1
μ
F low ESR,
low ESL capacitor.
VREF (Voltage Reference Output):
This pin provides
an accurate 5V reference, capable of delivering up to
10mA to external circuitry, and is internally short circuit
current limited. For best reference stability, bypass
VREF directly to the GND pin with a 0.1
μ
F, low ESR,
low ESL capacitor.
VSENSE (Output Voltage Sensing Input):
This pin is
the input to the OVP and PWRGOOD comparators and
is connected to the system output voltage through a
lowpass filter. When choosing the resistor value for this
filter, make sure that no more than 500
μ
A will flow
PIN DESCRIPTIONS (cont.)
UC1910
UC2910
UC3910
APPLICATION INFORMATION
The Overvoltage (OV), Undervoltage (UV) and Overvol-
tage Protection Voltage (OVP) threshold detection volt-
ages are programmed as a percentage about the
nominal DAC output voltage, DACOUT. Figure 1 illus-
trates how to program the UC3910 by setting a voltage
divider, R
DIV
, at the OVTH/UVTH pin. The voltage di-
vider ratio is defined as
R
DIV
=
RS1
RS1
+
RS2
The UC3910 allows a ratio R
DIV
at the OVTH/UVTH pin
from 0.3 to 0.9, which corresponds to overvoltage and
undervoltage percentage thresholds from 5% to 15%
and an OVP percentage threshold from 10% to 30%.
These thresholds are shown in Figure 2.
The OV, UV and OVP percentage thresholds are given
by
%V
OV
= R
DIV
16.7
%V
UV
= –(R
DIV
16.7)
%V
OVP
= %V
OV
2.0 = R
DIV
33.4
An R-C filter is added to the VSENSE pin to filter noise
and ripple at the comparator inputs. An R-C filter fre-
quency of F
SWITCH
/10 is recommended. Choose the
Figure 1. Setting the OV/UV/OVP Threshold
Percentages
UDG-96020
4
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