NCP4300A
http://onsemi.com
5
55
50
60
65
Figure 8. Common Mode Rejection Ratio
vs. Supply Voltage
V
CC
, SUPPLY VOLTAGE (V)
CMRR, COMMON MODE REJECTION RATIO (dB)
0302010 40
V
CC
= 3.0 V to 35 V
105°C
25°C
0°C
DETAILED OPERATING DESCRIPTION
INTRODUCTION
Power supplies and battery chargers require precise
control of output voltage and current in order to prevent
catastrophic damage to the system connected. Many present
day power sources contain a wide assortment of building
blocks and glue devices to perform the required sensing for
proper regulation. Typical feedback loop circuits may
consist of a voltage and current amplifier, summing circuitry
and a reference. The NCP4300A contains all of these basic
functions in a manner that is easily adaptable to many of the
various power source−load configurations.
OPERATING DESCRIPTION
The NCP4300A is an analog regulation control circuit that
is designed to simultaneously close the voltage and current
feedback loops in power supply and battery charger
applications. This device can control the feedback loop in
either constant−voltage (CV) or constant−current (CC)
mode with smooth crossover. A concise description of the
integrated circuit blocks is given in below. The functional
block diagram of the IC is shown in Figure 1.
Internal Reference
An internal precision band gap reference is used to set the
2.6 V voltage threshold and current threshold setting. The
reference is initially trimmed to a ±0.5% tolerance at
T
A
= 25_C and is guaranteed to be within ±1.0% over an
ambient temperature range of 0_C to 105_C.
Voltage Sensing Operational Amplifier (Op−Amp 1)
The internal Op−Amp 1 is designed to perform the voltage
control function. The non−inverting input of the op−amp is
connected to the precision voltage reference internally. The
inverting input of the op−amp monitors the voltage
information derived from the system output. As the control
threshold is internally connected to the voltage reference,
the voltage regulation threshold is fixed at 2.6 V. For any
output voltage from 2.6 V up to the maximum limit can be
configurated with an external resistor divider. The output
terminal of Op−Amp 1 (pin 1) provides the error signal for
output voltage control. The output pin also provides a means
for external compensation.
Independent Operational Amplifier (Op−Amp 2)
The internal Op−Amp 2 is configurated as a general
purpose op−amp with all terminals available for the user.
With the low offset voltage provided, 0.5 mV, this op−amp
can be used for current sensing in a constant current
regulator.
