Datasheet AP2952A Datasheet (Chipown)

AP2952A Chipown

2A, 18V Synchronous Rectified

Step-Down Converter

Description

The AP2952A is a monolithic synchronous buck regulator.
The device integrates 130mΩ MOSFETS that provide 2A
continuous load current over a wide operating input voltage
of 4.75V to 18V. Current mode control provides fast transient
response and cycle-by-cycle current limit.
An adjustable soft-start prevents inrush current at turn-on. In
shutdown mode, the supply current drops below 1μA.
This device, available in an 8-pin SOP package, provides a
very compact system solution with minimal reliance on
external components.

Applications

 Distributed Power Systems
 Networking Systems
 FPGA, DSP, ASIC Power Supplies
 Green Electronics/ Appliances


Notebook Computers

Features

 2A Output Current
 Wide 4.75V to 18V Operating Input Range
 Integrated 130mΩ Power MOSFET Switches
 Output Adjustable from 0.925V to 15V
 Up to 95% Efficiency
 Programmable Soft-Start
 Fixed 450KHz Frequency
 Cycle-by-Cycle Over Current Protection
 Input Under Voltage Lockout
 Thermally Enhanced 8-Pin SOP Package

Package

Typical Application Circuit

Vout=5V

100

90
80

70

60
50

40

Efficy(%)

30

20
10

0

0 400 800 120 0 160 0 2000

Figure 1. Typical Application Circuit

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Figure 2. Typical Efficiency Curve

Load(mA)

Vin=9V
Vin=12V
Vin=18V

AP2952A Chipown

θ

(2)

JC

Absolute Maximum Ratings

Supply Voltage (VIN)..................................-0.3V to 20V

Switch Voltage (VSW)......................–1V to VIN+ 0.3V

Bootstrap Voltage (VBS) ..........Vsw-0.3V to VSW+ 6V

Enable/UVLO Voltage (VEN)....................–0.3V to +6V

Comp Voltage (V

Feedback Voltage (VFB) ...........................–0.3V to +6V

Junction Temperature .................................... +150℃

Lead Temperature (Soldering, 10s)................... +260℃

Storage Temperature......................... –65°C to +150℃

) ..........................–0.3V to +6V

COMP

(1)

Recommended Operating Conditions

Input Voltage (VIN) ........................................ 4.75V to 18V

Output Voltage (VSW) .................................... 0.925 to 15V

Operating Temperature...................................–40℃to +85℃

(3)

Thermal Resistance

SOP8-PP ..............................50...... 10... ℃/W

Notes:

1) Exceeding these ratings may damage the device.

2) The device is not guaranteed to function outside of its
operating conditions.

3) Measured on approximately 1”square of 1 oz copper.

θ

JA

Electrical Characteristics

VIN= 12V, TA= +25℃, unless otherwise noted.

Parameter Condition Min Typ Max Units

Shutdown Supply Current

Supply Current VEN =2.0V, VFB = 1.0V 1.3 1.5 mA

Feedback Voltage

Feedback Overvoltage Threshold 1.1 V

Error Amplifier Voltage 400 V/V

Error Amplifier Transconductance ΔIC = ±10μA 800 µA/V

High-Side Switch-On Resistance 130 mΩ

Low-Side Switch-On Resistance 130 mΩ

High-Side Switch Leakage VEN = 0V, VSW = 0V 10 µA
Upper Switch Current Limit 2.4 3.4 A

Lower Switch Current Limit 1.1 A

COMP to Current Sense Transconductance 3.5 А/V

Oscillator Frequency 450 KHz

Short Circuit Frequency VFB = 0V 150 KHz

Maximum Duty Cycle VFB = 1.0V 90 %

Minimum On Time 220 nS

EN Shutdown Threshold Voltage VEN Rising 1.1 1.5 2.0 V

EN Shutdown Threshold Voltage Hysterisis 40 mV

EN Lockout Threshold Voltage 2.2 2.5 2.7 V

EN Lockout Hysterisis 210 mV

Input UVLO Threshold Rising VIN Rising 3.8 4.1 4.4 V

VEN ≤ 0.3V

4.75V≤VIN ≤18V

900 925 946 mV

1 3 µA

Input UVLO Threshold Hysteresis 210 mV

Soft-start Current VSS = 0V 6 µA

Soft-start Period CSS = 0.1μF 15 ms

Thermal Shutdown 160 °C

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AP2952A Chipown

Channel

r the high

down converter switches.

Drive IN with a 4.75V to 18V power source. Bypass IN to GND with a suitably large

Power Switching Output. SW is the switching node that supplies power to the output.

Connect the output LC filter from SW to the output load. Note that a capacitor is required

Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a

resistive voltage divider from the output voltage. The feedback threshold is 0.925V. See

a series RC network from COMP to GND to compensate the regulation control loop. In

ation

on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.

start period. Connect a capacitor from SS to

start period to 15ms. To

Ordering Information

Part number Mark

AP2952AS8T

AP2952AS8R

1． Y=year

W=week

Pin Configuration

Pin Description

Pin # Name Description

1 BS

2952

YYWW

2952

YYWW

1

1

1

2

3

4

Package Temperature

SOP8&IC tube

SOP8&Embossed tape

8

7

6

5

–40℃ to +85℃

–40℃ to +85℃

High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N­MOSFET switch. Connect a 0.01μF or greater capacitor from SW to BS to powe
side switch.

Power Input. IN supplies the power to the IC, as well as the step-

2 IN

capacitor to eliminate noise on the input to the IC. See Input Capacitor.

3 SW

from SW to BS to power the high-side switch.

4 GND Ground(Connect Exposed Pad to Pin 4)..

5 FB

Setting the Output Voltage.

Compensation Node. COMP is used to compensate the regulation control loop. Connect

6 COMP

some cases, an additional capacitor from COMP to GND is required. See Compens

Components.

7 EN

Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn

Soft-Start Control Input. SS controls the soft-

8 SS

GND to set the soft-start period. A 0.1μF capacitor sets the soft-
disable the soft-start feature, leave SS unconnected.

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AP2952A Chipown

Functional Description

The AP2952A is a synchronous rectified, current-mode,
step-down regulator. It regulates input voltages from 4.75V to
18V down to an output voltage as low as 0.925V, and supplies
up to 2A of load current.
The AP2952A uses current-mode control to regulate the output
voltage. The output voltage is measured at FB through a
resistive voltage divider and amplified through the internal
transconductance error amplifier. The voltage at the COMP pin
is compared to the switch current measured internally to
control the output voltage.

Functional Block Diagram

The converter uses internal N-Channel MOSFET switches to
step-down the input voltage to the regulated output voltage.
Since the high side MOSFET requires a gate voltage greater
than the input voltage, a boost capacitor connected between
SW and BS is needed to drive the high side gate. The boost
capacitor is charged from the internal 5V rail when SW is low.
When the AP2952A FB pin exceeds 20% of the nominal
regulation voltage of 0.925V, the over voltage comparator is
tripped and the COMP pin and the SS pin are discharged to
GND, forcing the high-side switch off.

Figure 3 Functional Block Diagram

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Application Information

Component Selection
Setting the Output Voltage

The output voltage is set using a resistive voltage divider
from the output voltage to FB (see Typical Application
circuit on page 1). The voltage divider divides the output
voltage down by the ratio:

Where VOUT is the output voltage, VIN is the input voltage,
fS is the switching frequency, and ΔIL is the peak- to-peak
inductor ripple current.
Choose an inductor that will not saturate under the maximum
inductor peak current. The peak inductor current can be
calculated by:

Where VFBis the feedback voltage and V
voltage.

Thus the output voltage is:

R2 can be as high as 100kΩ, but a typical value is 10kΩ.
Using the typical value for R2, R1 is determined by:

For example, for a 3.3V output voltage, R2 is 10kΩ, and R1

is 26.1kΩ. Table 1 lists recommended resistance values of R1

and R2 for standard output voltages.

OUT

is the output

Where ILOAD is the load current.
The choice of which style inductor to use mainly depends on
the price vs. size requirements and any EMI requirements.

Optional Schottky Diode

During the transition between high-side switch and low-side
switch, the body diode of the lowside power MOSFET
conducts the inductor current. The forward voltage of this
body diode is high. An optional Schottky diode may be
paralleled between the SW pin and GND pin to improve
overall efficiency. Table 2 lists example Schottky diodes and
their Manufacturers.

Inductor

The inductor is required to supply constant current to the
output load while being driven by the switched input voltage.
A larger value inductor will result in less ripple current that
will result in lower output ripple voltage. However, the larger
value inductor will have a larger physical size, higher series
resistance, and/or lower saturation current. A good rule for
determining the inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately 30% of the
maximum switch current limit. Also, make sure that the peak
inductor current is below the maximum switch current limit.
The inductance value can be calculated by:

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Input Capacitor

The input current to the step-down converter is discontinuous,
therefore a capacitor is required to supply the AC current to
the step-down converter while maintaining the DC input
voltage. Use low ESR capacitors for the best performance.
Ceramic capacitors are preferred, but tantalum or low-ESR
electrolytic capacitors may also suffice. Choose X5R or X7R
dielectrics when using ceramic capacitors. Since the input
capacitor absorbs the input switching current it requires an
adequate ripple current rating. The RMS current in the input
capacitor can be estimated by:

AP2952A Chipown

Compensation Components

AP2952A employs current mode control for easy
compensation and fast transient response. The s ystem

The worst-case condition occurs at VIN = 2VOUT, where
ICIN = ILOAD/2. For simplification, choose the input
capacitor whose RMS current rating greater than half of the
maximum load current. The input capacitor can be
electrolytic, tantalum or ceramic. When using electrolytic or
tantalum capacitors, a small, high quality ceramic capacitor,
i.e. 0.1μF, should be placed as close to the IC as possible.
When using ceramic capacitors, make sure that they have
enough capacitance to provide sufficient charge to prevent
excessive voltage ripple at input. The input voltage ripple for
low ESR capacitors can be estimated by:

Where C1 is the input capacitance value.

Output Capacitor

The output capacitor is required to maintain the DC output
voltage. Ceramic, tantalum, or low ESR electrolytic capacitors
are recommended. Low ESR capacitors are preferred to keep
the output voltage ripple low. The output voltage ripple can be
estimated by:

stability and transient response are controlled through the
COMP pin. COMP pin is the output of the internal
transconductance error amplifier. A series capacitorresistor
combination sets a pole-zero combination to control the
characteristics of the control system.
The DC gain of the voltage feedback loop is given by:

Where VFB is the feedback voltage, 0.925V;
AVEA is the error amplifier voltage gain; GCS is the current
sense transconductance and RLOAD is the load resistor value.
The system has two poles of importance. One is due to the
compensation capacitor (C3) and the output resistor of the
error amplifier, and the other is due to the output capacitor
and the load resistor. These poles are located at:

Where GEA is the error amplifier transconductance.

Where C2 is the output capacitance value and

RESR is the equivalent series resistance (ESR) value of the
output capacitor. In the case of ceramic capacitors, the
impedance at the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly caused by the
capacitance. For simplification, the output voltage ripple can
be estimated by:

In the case of tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching frequency. For
simplification, the output ripple can be approximated to:

The characteristics of the output capacitor also affect the
stability of the regulation system. The AP2952A can be
optimized for a wide range of capacitance and ESR values.
For AP2952A normal operation, the output can be an
electrolytic capacitor in parallel.

The system has one zero of importance, due to the
compensation capacitor (C3) and the compensation resistor
(R3). This zero is located at:

The system may have another zero of importance, if the
output capacitor has a large capacitance and/or a high ESR
value. The zero, due to the ESR and capacitance of the output
capacitor, is located at:

In this case (as shown in Figure 4), a third pole set by the
compensation capacitor (C6) and the compensation resistor
(R3) is used to compensate the effect of the ESR zero on the
loop gain. This pole is located at:

The goal of compensation design is to shape the converter
transfer function to get a desired loop gain. The system
crossover frequency where the feedback loop has the unity
gain is important. Lower crossover frequencies result in slower
line and load transient responses, while higher crossover
frequencies could cause system instability. A good rule of

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AP2952A Chipown

thumb is to set the crossover frequency below one-tenth of the
switching frequency.

To optimize the compensation components, the following
procedure can be used.

1. Choose the compensation resistor (R3) to set the desired
crossover frequency. Determine the R3 value by the following
equation:

Where fC is the desired crossover frequency which is

typically below one tenth of the switching frequency.

2. Choose the compensation capacitor (C3) to achieve the
desired phase margin. For applications with typical inductor
values, setting the compensation zero, fZ1, below one-forth of
the crossover frequency provides sufficient phase margin.

Determine the C3 value by the following equation:

Where R3 is the compensation resistor.

3. Determine if the second compensation capacitor (C6) is
required. It is required if the ESR zero of the output capacitor
is located at less than half of the switching frequency, or the
following relationship is valid:

If this is the case, then add the second compensation
capacitor (C6) to set the pole fP3 at the location of the ESR
zero. Determine the C6 value by the equation:

External Bootstrap Diode

An external bootstrap diode may enhance the efficiency of the
regulator, the applicable conditions of external BS diode are:

● VOUT is 5V or 3.3V; and

● Duty cycle is high: D=VOUT/VIN >65%

In these cases, an external BS diode is recommended from the
output of the voltage regulator to BS pin, as shown in Figure4

Figure 4 Add Optional External Bootstrap Diode to

Enhance Efficiency
The recommended external BS diode is IN4148, and the BS
cap is 0.1~1µF.

Typical Performance Characteristics

Channel1:EN, Channel3:VO

VIN=12V,VO=3.3V,No Load

Soft-Start shutdown

Ripple Transient response(Iout=0-2A)

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AP2952A Chipown

Typical Application Circuits

Figure 5 AP2952A with 3.3V output, 2X22uF Ceramic Output Capacitor

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AP2952A Chipown

Package Information

SOP8-PP

Important Notice

Chipown Microelectronics Co. Ltd. reserves the right to make changes without further notice to any products or specifications
herein. Chipown Microelectronics Co. Ltd. does not assume any responsibility for use of any its products for any particular purpose,
nor does Chipown Microelectronics Co. Ltd assume any liability arising out of the application or use of any its products or circuits.
Chipown Microelectronics Co. Ltd does not convey any license under its patent rights or other rights nor the rights of others.

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