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ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller Preliminary
Contents
1. AP2011 Specification
1.1 1.2 1.3 1.4 Features General Description Pin Assignments Pin Descriptions
1.5 Block Diagram 1.6 Absolute Maximum Ratings
2. Hardware
2.1 2.2 2.3 2.4 Introduction Description of the built-in function circuit Schematic Board of Material
2.5 Board Layout
3. Design Procedure
3.1 Introduction 3.2 Operating Specifications 3.3 Design Procedures
4. Design Example
4.1 Summary of Target Specifications 4.2 Calculating and Component Selections 4.3 Efficiency Calculation
This application note contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of this product. No rights under any patent accompany the sale of the product. Rev. A.0 Oct. 29, 2004 1/15
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller Preliminary
1. AP2011 Specification 1.1 Features
- Single 10V to 40V Supply Application - 1.25V + 2.0% Voltage Reference. - Virtual Frequency ControlTM. - Fast transient response. - Synchronous operation for high efficiency - Current limit function. - Small size with minimum external components - Soft Start and Shutdown functions - Industrial temperature range - Under Voltage Lockout function - SOP-14L Pb-Free package
1.2 General Description
The AP2011 integrates Pulse-width-Modulation (PWM) control circuit into a single chip, mainly designs for power-supply regulator. All the functions included an on-chip 1.25V reference voltage, a smart auto modulated oscillator, UVLO, SCP, circuitry, and synchronous PWM controller circuit. Recommend the output CE transistors as pre-driver for Driving externally. Switching frequency can be adjustable by Virtual Frequency Control. During low VCC situation, the UVLO makes sure that the outputs are off until the internal circuit is operational normally.
1.3 Pin Assignments
1.4 Pin Descriptions
Pin Name PGATE VCC PVCC PDRV PGND NGATE VIN CAP SS/ SHDN FB OCSET SGND PHASE VREF No. 1
(Top View) PGATE VCC PVCC PDRV PGND NGATE VIN
1 2 3 5 6 7
14 13 12 10
4 AP2011 11 9
8
VREF PHASE SGND OCSET FB SS/SHDN CAP
2 3 4
5 6
7
8 9 10 11 12 13
SOP-14L
14
Description Level shift-gate driver Internal regulator voltage Power VCC PMOS Gat driver Power Ground Low side driver output (N MOSFET) Chip supply voltage Charge pump pin Soft start, a capacitor to ground sets the slow start time/set low for shutdown function. Feedback input Sets the converter over-current trip point Signal Ground Input from the phase node between the MOSFETs Reference voltage
Anachip Corp. www.anachip.com.tw 2/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 1.5 Block Diagram
GND VCC 1.25V VOLTAGE REFERENCE + VREF INTERNAL REGULATOR 8V PGATE BIAS + VIN CAP PGATE OCSET PHASE 70uA ERROR COMP +
Preliminary
UNDER VOLTAGE
-
-
FB SS/SHDN
+
PVCC R S CROSS CURRENT CONTROL Q DRVP PDRV
-
-
0.3V VCC 12ua
VIRTUAL FREQ OSCILLATOR 200kHz
2ua
DRVN
NGATE PGND
0.2V
+
-
Q
S
QB R + 0.9V
Virtual Frequency Control - Patent Number 6,456,050.
-
AP2011 FUNCTIONAL BLOCK DIAGRAM
1.6 Absolute Maximum Ratings
Symbol VIN VPHASE JC JA TOP TST TLEAD VCC to GND PHASE to GND Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 Sec. Parameter Range. 0 to 42 0 to 42 60 150 -40 to +85 -65 to +150 300
o o
Unit V V C/W C/W
o o o
C C C
Anachip Corp. www.anachip.com.tw 3/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 2. Hardware 2.1 Introduction
AP2011 is a high efficiency and high performance synchronous PWM controller. With using one P-channel MOSFET and one N-channel MOSFET to be the synchronous switch, AP2011 can make the system operating in more than 92% efficiency situation. There are a lots of function built inside in AP2011 like programmable current limit, UVLO, soft-start, shutdown, reference voltage, voltage clamping for high input voltage, and the most important function is the Virtual Frequency Control , which make the frequency modulated automatically by the input and output voltage of the system. The functions' description will show in each section to let user know how to define the outside circuit.
TM
Preliminary
2.2 Description of the built-in function
Programmable Current Limit Control
The programmable current limit control circuit is designed for engineer who needs to control the limit current to avoid too large system current. The current limit set pin (OCSET) just needs to add an outside resistor between VCC and OCSET pin, which resistor can make a voltage drop to VCC with the internal current source (70uA). This voltage drop will compare with the voltage drop of PWM waveform (Phase pin waveform) because the voltage drop of PWM is made by output current and P-channel MOSFET RDSON, so we can limit the output current by this formula:
I
LOAD
x R DS ( on ) - PMOS =
I
OCSET
x ROCSET
If the comparator detected the PWM high voltage level is under the OCSET pin voltage level, it will sent turn off signal to shutdown the PWM control and SS pin will discharge the outside capacitor with a 2uA current. After SS pin voltage lower than 0.2V, AP2011 will reset to make PWM and start to charge SS pin. If SS pin charges to 0.9V but PWM still lower than OCSET voltage, then the comparator will send the signal to shutdown PWM again.
OCSET IOCSET PHASE +
DRVP
-
PWM Control DRVN
Figure 1. Programmable Current Limit Control Circuit
Anachip Corp. www.anachip.com.tw 4/15 Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller
Under Voltage Lock Out (UVLO)
The circuit shown in Figure 2 is a simple explanation of UVLO function. VCC voltage will make that two resistors get a compared voltage with VREF. AP2011 is designed for UVLO voltage is 6.5V, and recovery voltage is 6.8V (that 0.3V voltage is depend on the offset voltage of the comparator). If VCC voltage is lower than 6.5V, the separate voltage of those two resistors is under 1.25V, than that comparator will send low level signal to SS pin to shutdown AP2011. And if VCC is higher than 6.8V, that comparator will send high level signal to SS and AP2011 will start to enter normal operation mode.
VCC VREF 1.25V VREF +
Preliminary
-
SS/SHDN
Figure 2. Under Voltage Lock-Out circuit
Soft-Start and Shutdown ( SS/ SHDN )
The circuit shown in Figure 3 is about soft-start and shutdown function. If outside system force SS pin always under 0.2V, AP2011 will turn into shutdown mode and turn off the PWM. When SS pin higher than 0.2V, PWM will turn on to drive outside MOSFET, but now PWM duty is depend on the comparison of SS and FB. According to SS pin raising curve, FB will follow this curve until SS reaches to VREF + 0.3V, and then PWM duty will turn to depend on the comparison of VREF and FB.
VREF FB VCC 10uA SS/SHDN +0.3V
+ +
-
DRVP + 2uA 0.2V 0.9V
-
PWM Control DRVN
+
Figure 3. Soft-start and Shutdown circuit
Anachip Corp. www.anachip.com.tw 5/15 Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller
Voltage Clamping for High Input Voltage
Normally the MOSFETs AP2011 used can be bought easily, but always the easy-buying parts have 25V VGS maximum rating. If we use AP2011 in more than 25V input voltage system, we need a voltage clamping function for protecting the MOSFETs. AP2011 is built-in a 8V voltage drop circuit to clamp the voltage between VIN to PGATE, and NGATE to GND. This 8V voltage will show in PVCC pin to GND and make PDRV to PGATE always keep a VIN-8V voltage. In this function's operation, first we add a capacitor outside in CAP pin (Figure. 4), AP2011 will make a current to charge the outside capacitor by the resistor. And if that charging current is large enough to make the voltage of that resistor larger than VBE of the PNP, the PNP will turn on and have ICE passing through. This current will be mirrored to make charging current of CBOOST. We need choose a suitable capacitor for CAP pin to make sure that charging current is enough for CBOOST. If Ccap value is not enough, the P channel MOSFET may conduct a large short-through current during supply transition.
Preliminary
VCC ICAP CAP Ccap R
VCC PGATE + 0.7V Mirror Cboost
ICE
PDRV Ccap > 20*Cboost Cboost = 47nF (recommendation) outside inside
Figure 4. Voltage Clamping Function Circuit
Virtual Frequency Control
Virtual Frequency Control combines the advantages of constant frequency and constant off-time control in a single mode of operation. This allows fix frequency, precision switching voltage regulator control with fast transient response and the smallest solution size. Switch duty cycle can be adjusted from 0% to 100% on a pulse by pulse basis when responding to transient conditions. Both 0% and 100% duty cycle operation can be maintained for extended periods of time in response to load or line transients. Figure 5 depicts a simplified operation of the Virtual Frequency Control technique: The VFC oscillator generates a pulse of a known duration (VFC_Pulse). The regulator loop responds by returning a complementary feedback pulse (FB_Pulse). The FB_Pulse duration is a result of external conditions such as inductor size, the voltage
Anachip Corp. www.anachip.com.tw 6/15 Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller Preliminary
across the inductor and the duration of the VFC_Pulse. A VFC control loop is then formed whereby the duration of the VFC_Pulse is modified as a result of the FB_Pulse duration. The VFC loop arrives at a state of equilibrium, where the operating frequency remains inherently constant.
VIN
ERROR COMP Vref
+
-
GATE CONTROL LOGIC VFC Pulse FB Pulse
Lout Cout
Vout Rfb1 Rfb2
VIRTUAL FREQ OSCILLATOR
DON > 0.1, 240-50 x (1DON < 0.1,
) - VIN VIN 10000 x VOUT/ VIN 5.9 - 0.01VIN
VOUT
Figure 5: Virtual Frequency Control LoopSynchronous single supply application. Virtual frequency control is a technique that provides stable, constant frequency of operation for pulse controlled architectures such as constant off-time/on-time. This is all done internal to the IC with minimal number of components and without the need for connections to external terminals such as input and/or output. No external compensation is required, thus providing a low cost, high performance fix frequency solution for switching voltage regulators. Virtual Frequency Control is a trademark of PWRTEK, LLC.
Anachip Corp. www.anachip.com.tw 7/15
Rev. A.0 Oct, 29, 2004
Anachip Corp. www.anachip.com.tw
2.3 Schematic
VCC_20V
20V
R4 20K U1 C3
PMOS
R3 6.8
AP2011 G Q3 AF4435 D 47nF D L2 33uH
S
Vout=1.25*(R7+R9)/R9
CN1 5V/5A
C1
C4
470uF/35V 10nF
14 13 12 11 10 9 8 BP PGATE PHASE Vcc SGND VCCPWR OSCSET PDRV FB PGND SS NGATE CAP Vin
1 2 3 4 5 6 7
4 3 2 1 C5 150nF C13 10nF
Application Note AP2011 High Efficiency Synchronous PWM Controller
Figure 5. AP2011 Application Circuit
8/15
G C9 0.1uF 330nF 1uF 330nF 0.1uF C10 C11 C6 C7 S Q5 AF4410
NMOS
4 3 2 1 R7 3K 1% D5 optional 2.5mm 4X1
C12
R8 0 R9 1K 1%
680uF/16V LOW ESR
ANP015
Rev. A.0 Oct, 29, 2004
Preliminary
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 2.4 Board of Materials
No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Value Q'ty Part Reference AP2011 1 U1 470uF/35V 1 C1 47nF/50V 1 C3 10nF/50V 2 C4, C13 150nF/50V 1 C5 330nF/50V 2 C6, C10 0.1uF/50V 2 C7, C9 1uF/50V 1 C11 680uF/16V 1 C12 6.8 1 R3 3K 2 R4, R7 1K 1 R9 0 1 R8 SB340 1 D5 33uH 1 L2 AF4435 1 Q3 AF4410 1 Q5 Connecter CN1 Description AP2011 Low ESR 0805 ceramic SMD capacitor 0805 ceramic SMD capacitor 0805 ceramic SMD capacitor 0805 ceramic SMD capacitor 0805 ceramic SMD capacitor 0805 ceramic SMD capacitor Low ESR 1% 0805 SMD resistor 1% 0805 SMD resistor 1% 0805 SMD resistor 1% 0805 SMD resistor optional ring core inductor 5A 30V 10A P-MOSFET 30V 10A N-MOSFET Manufacturers Part Number Anachip AP2011 OST Viking Tech Viking Tech Viking Tech Viking Tech Viking Tech Viking Tech OST Viking Tech Viking Tech Viking Tech Viking Tech Viking Tech Anachip Anachip
Preliminary
Anachip Corp. www.anachip.com.tw 9/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 2.5 Board Layout
Top Side
Preliminary
Bottom Side
Anachip Corp. www.anachip.com.tw 10/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 3. Design Procedure 3.1 Introduction
The AP2011 integrated circuit is a synchronous PWM controller, it operates over a wide input voltage range. Being low cost, it is a very popular choice of PWM controller. This section will describe the AP2011 design procedure. The operation and the design of this application will also be discussed in detail.
Preliminary
3.2 Operating Specifications
Specification Input Voltage Output Voltage Operating Frequency Output power Min 18 4.9 160 0 Typ 20 5 180 25 Max 22 5.1 200 30 Units V V KHz W
Table 1. Operating Specifications
3.3 Design Procedures
This section describes the steps to design synchronous buck converter, and explains how to construct basic power conversion circuits including the design of the control chip functions and the basic loop.
Synchronous buck converter
Example calculations accompany the design equations. Since this is a buck output system, this example calculations apply to the converter with output power is 60W and input voltage set to 25V, unless specified otherwise. The first quantity to be determined is the converter the duty cycle value. Vo + VDS(sat),N VIN - VDS(sat),P + VDS(sat),N Ton Ts
Duty ratio
D=
=
,
0D1
Assuming the low-side N-channel MOSFET switch-on voltage VDS(sat),N = 0.1 V, the high-side P-channel MOSFET switch on voltage VDS(sat),P = 0.1V and Vo = 5V. In this case the duty cycle for VIN = 20V is 0.255 for 5V/5A output system.
Anachip Corp. www.anachip.com.tw 11/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller
Inductor Selection
The inductor plays a central role in the proper operation of the buck circuit. To find the inductor value it is necessary to consider the inductor ripple current. Choose an inductor to maintain continuous-mode operation down to 10 percent (Io(min)) of the rated output load: IL = 2 x 10% x Io = 2 x 0.1 x 5 = 1A The inductor "LB" value for this system is connected to be: (Vin - Vds(sat) - Vo) x Dmin IL x fs (25 - 0.1 - 12) x 0.484 1 x (180 x 10^3)
Preliminary
LB
=
= 21H
So we choose buck inductor value to be 33uH for this case, and if the core loss is a problem, increasing the inductance of L will be helpful.
Output Capacitor Selection
A. The output capacitor is required to filter the output and provide regulator loop stability. When selecting an output capacitor, the important capacitor parameters are; the 100KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is the most important parameter. The ESR can be calculated from the following formula.
ESR = V RIPPLE 2x I LOAD (min)
An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings may be needed to provide the low ESR values required for low output ripple voltage. If the selected capacitor's ESR is extremely low, resulting in an oscillation at the output. It is recommended to replace this low ESR capacitor by using two general standard capacitors in parallel. B. The capacitor voltage rating should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low ESR requirements needed for low output ripple voltage.
Anachip Corp. www.anachip.com.tw 12/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller
Output P-channel MOSFET and N-channel MOSFET Selection
A. The current ability of the output P-channel and N-channel MOSFETs must be at least larger than the peak switch current IPK. The voltage rating VDS of the P-channel and N-channel MOSFETs should be at least 1.25 times the maximum input voltage. B. The MOSFETs must be fast (switch time) and must be located close to the AP2011 using short leads and short printed circuit traces. In case of a large output current, we must layout a copper to reduce the temperature of these two MOSFETs. Because of their fast switching speed and low DS(ON) resistor (RDS(ON)), the Anachip AF44XX series provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications.
Preliminary
Input Capacitor Selection
A. The RMS current rating of the input capacitor can be calculated from the following formula table. The capacitor manufactured by data sheet must be checked to assure that this current rating is not exceeded. Calculation Step-down (buck) regulator
I I I I
PK
m L
Ton/(Ton+Toff) I LOAD(max) - I LOAD(min)
I
LOAD (max)
+ I LOAD (min)
2 x I LOAD(min)
IN ( rms )
x (I PK x I m ) +

1 ( I L )2 3
B. This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage.
Anachip Corp. www.anachip.com.tw 13/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 4. Design Example 4.1 Summary of Target Specifications
Input Power Regulated Output Power Output Ripple Voltage Output Voltage Load Regulation Efficiency Switching Frequency
Preliminary
V V V
IN (max)
OUT
= +20V;
V
IN (min)
= +20V
= + 5V;
I
LOAD(max)
= 5A;
I
LOAD(min)
= 0.5A
RIPPLE
50 mV peak-to-peak
1% (0.2A to 5A) 87% minimum at full load. F = Virtual Control (180KHz 10 %)
4.2 Calculating and Components Selection
Calculation Formula
VOUT=VFB x ((R7/R9) + 1)
L(min)
[V
IN (min)
- V SAT - V OUT x T ON (max) 2 x I LOAD (min) - I LOAD (min)
]
Select Condition 560 R9 5K
Component spec. R9=1k; R7=3k Select L2=33uH
L
(min)
21uH
PK
I
PK
=
I
I
rms
I
= 4.5A
LOAD (max)
ESR = V RIPPLE 2x I LOAD (min) V WVDC 1.5 xV OUT
1 2 I IN ( rms ) = x (I PK x I m ) + 3 ( I L ) V WVDC 1.5 xV IN (max)
ESR 50m V WVDC 7.5V
Select C12 680uF/16V*1pcs
I
ripple
I
IN ( rms )
=2.5A
V
WVDC
30V
Select C1 470uF/35V*1pcs
Anachip Corp. www.anachip.com.tw 14/15
Rev. A.0 Oct, 29, 2004
ANP015
Application Note AP2011 High Efficiency Synchronous PWM Controller 4.3 Efficiency Calculation
Vin(V) 20.09 20.01 20.1 20.02 20.05 Iin(A) 0.28 0.55 0.83 1.12 1.42 Vout(V) 4.99 4.98 4.98 4.98 4.97 Iout(A) 1 2 3 4 5 Eff(%) 88.70796 90.5002 89.55224 88.83973 87.2818
Preliminary
Eff(%)
92 90 88 86 0 1 2 3 4
Iout(A)
5
AP2011 Temperature VS Efficiency
Parameter -40 Vin(V) Iin(A) Vout(V) Iout(A) Efficiency (%) 20.04 0.29 4.85 1 -25 20.02 0.28 4.94 1 0 20.01 0.28 4.94 1
Temperature()
25 20.03 0.28 4.92 1 50 20.06 0.28 4.89 1 75 20.10 0.28 4.87 1 100 20.06 0.28 4.84 1 125 20.03 0.28 4.78 1
83.453 88.162 88.170 87.725 87.060 86.531 86.170 88.385
Written by Maverick Huang
Anachip Corp. www.anachip.com.tw 15/15
Rev. A.0 Oct, 29, 2004

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