General Description
The
ZA3020
is a monolithic step down switch
mode converter with a built in internal Power
MOSFET. It achieves 2A continuous output
current over a wide input supply range with
excellent load and line regulation.
Current mode operation provides fast transient
response and eases loop stabilization.
Fault condition protection includes cycle-by-
cycle current limiting and thermal shutdown. In
shutdown mode the regulator draws 23A of
supply current.
The
ZA3020
requires a minimum number of
readily available standard external
components. A synchronization pin allows the
part to be driven to 600KHz.
Ordering Information
Part Number
Package Temperature
ZA3020D
S
SOIC8
-40 to +125
C
. For Tape & Reel use suffix - Z (e.g. ZA3020DS-Z)
Features
2A Output Current
0.18 Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic
capacitors
Up to 95% Efficiency
20A Shutdown Mode
Fixed 380kHz frequency
Thermal Shutdown
Cycle-by-cycle over current protection
Wide 4.75 to 25V operating input range
Output Adjustable from 1.22 to 21V
Programmable under voltage lockout
Frequency Synchronization Input
Available in 8 pin SO package
Evaluation Board Available
Applications
Distributed Power Systems
Battery Charger
Pre-Regulator for Linear Regulators
Figure 1: Typical Application Circuit
70
75
80
85
90
95
0
0.5
1
1.5
2
Output Current (A)
E
ffi
ci
ency (%
)
5.0V
3.3V
2.5V
SHUTDOWN
IN
BS
FB
COMP
GND
EN
SNYC
V
IN
4.75 to 25V
IN
ENABLE
OPEN
V
OUT
2.5V/2A
NOT USED
ZA3020
Efficiency versus Output
Current and Voltage. V
IN
=10V
SW
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com 1
Absolute Maximum Ratings
(
Note 1)
Recommended Operating Conditions
(Note 2)
Supply Voltage (V
IN
)
28V Input Voltage (V
IN
)
4.75V to 25V
Switch Voltage (V
SW
)
-1V to V
IN
+1V Operating Temperature
-40 to +125
C
Boost Voltage
V
SW
+ 6V
Feedback Voltage (V
FB
)
0.3 to 6V
Enable/UVLO Voltage (V
EN
)
0.3 to 6V
Comp Voltage (V
COMP
)
0.3 to 6V
Sync Voltage (V
SYNC
)
0.3 to 6V
Package Thermal Characteristics
Junction Temperature
150
C Thermal Resistance
JA
(SOIC8)
105
C/W
Lead Temperature
260
C
Storage Temperature
-65 to +150
C
Electrical Characteristics
(Unless otherwise specified V
IN
=12V, T
A
=25 C)
Parameters Condition
Min
Typ
Max
Units
Feedback Voltage
4.75V
V
IN
25V
V
COMP
< 2V
1.198 1.222 1.246 V
Upper Switch On Resistance
0.18
Lower Switch On Resistance
10
Upper Switch Leakage
V
EN
=0V; V
SW
=0V
0
10
A
Current Limit
2.4
2.85
3.3
A
Current Limit Gain.
Output Current to Comp Pin Voltage
1.95
A/V
Error Amplifier Voltage Gain
400
V/V
Error Amplifier Transconductance
I
C
=
10 A
500 770 1100
Mho
Oscillator Frequency
342
380
418
KHz
Short Circuit Frequency
V
FB
= 0V
30
42
54
KHz
Sync Frequency
Sync Drive 0 to 2.7V
445
600
KHz
Maximum Duty Cycle
V
FB
= 1.0V
90
%
Minimum Duty Cycle
V
FB
= 1.5V
0
%
Enable Threshold
I
CC
> 100A
0.7
1.0
1.3
V
Enable Pull Up Current
V
EN
= 0V
1.15
1.46
1.8
A
Under Voltage Lockout Threshold High Going
2.37
2.495
2.62
V
Under Voltage Lockout Threshold Hysteresis
210
mV
Supply current (quiescent)
V
EN
0.4V
23
36
A
Supply current (operating)
V
EN
2.6V; V
FB
=1.4V
1.0
1.2
mA
Thermal Shutdown
160
C
Note 1. Exceeding these ratings may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Measured on approximately 1" square of 1 oz. copper surrounding device leads.
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
2
Figure 2: Functional Block Diagram
40/400KHz
Oscillator
Slope
Compensation
1.8V
Current
Comparator
8
Internal
Regulators
2
1uA
2.30/2.53V
0.7V
7
Shutdown
Comparator
Lockout
Comparato
r
3
4
M2
10 ohm
M1
0.2 ohm
6
1.22V
5
Error Amplifier
gm= 630uA/Volt
IN
SYNC
EN
COMP
FB
GND
SW
BS
1
0.7V
Frequency
Foldback
Comparator
5V
CLK
S
R
Q
Q
Current
Sense
Amplifier
Functional Description
The
ZA3020
is a current mode r egulator. That is,
the compensation pin voltage is proportional to the
current delivered to the load.
At the beginning of a cycle: the upper transistor M1
is off; the lower transistor M2 on; the COMP pin
voltage is higher than the current sense amplifier
output; and the current comparator's output is low.
The rising edge of the 380KHz CLK signal sets the
RS Flip-Flop. Its output turns off M2 and turns on
M1 thus connecting the Switch pin and inductor to
the Input supply. The increasing inductor current is
sensed and amplified by the Current Sense
Amplifier. Ramp compensation is summed to
Current Sense Amplifier output and compared to
the error amplifier output by the Current
Comparator. When the Current Sense Amplifier
plus Slope Compensation signal exceeds the
Comp pin voltage, the RS Flip-Flop is reset and the
chip reverts to its initial M1 off, M2 on state.
If the Current Sense Amplifier plus Slope
Compensation signal does not exceed the COMP
voltage, then the falling edge of the CLK resets the
Flip-Flop.
The output of the Error amplifier integrates the
voltage difference between the feedback and the
1.22V bandgap reference. The polarity is such that
feedback pin voltages lower than 1.22V increases
the COMP pin voltage. Since the COMP pin's
voltage is proportional to the peak inductor current
an increase in its voltage increases current
delivered to the output.
The lower 10 switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
most of the inductor current.
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
3
Pin Descriptions
Pin 1: BS - Bootstrap - C5
This capacitor is needed to drive the power
switch's gate above the supply voltage. It is
connected between SW and Bootstrap pins to
effect a floating supply across the power switch
driver. The voltage across C5 is about 5V and is
supplied by the internal +5V supply when the SW
pin voltage is low.
Pin 2: IN - Supply Voltage
The
ZA3020
operates from a +4.75V to +25V
unregulated input. C1 is needed to prevent large
voltage spikes from appearing at the input.
Pin 3: SW - Switch
This connects the inductor to either IN through M1
or to GND through M2.
Pin 4: GND - Ground
This pin is the voltage reference for the regulated
voltage. For this reason care must be taken in its
layout. This node should be placed outside of the
D
SCH
to C1 ground path to prevent switching
current spikes to induce voltage noise into the
part.
Pin 5: FB - Feedback
An external resistor divider from the output voltage
to GND, tapped to the FB pin sets the output
voltage. To prevent current limit run away during
a short circuit fault condition the frequency fold
back comparator lowers the oscillation frequency
when the FB voltage is below 650mV.
Pin 6: COMP - Compensation
This node is the output of the transconductance
error amplifier and the input to the current
comparator. Frequency compensation is done at
this node by connecting a series R-C to ground.
See the compensation section for exact details.
Pin 7: EN - Enable/UVLO
A voltage greater than 2.495V enables operation.
Leave the input unconnected if unused. An Under
Voltage Lockout (UVLO) function can be
implemented by the addition of a resistor divider
from V
IN
to GND. For complete low current
shutdown its needs to be less than 0.7V.
Pin 8: SYNC - Synchronization Input
This pin is used to synchronize the internal
oscillator frequency to an external source. There
is an internal 11K pull down resistor to GND
hence leave the input unconnected if unused.
Sync Pin Operation
The SYNC pin driving waveform should be a
square wave with a rise time of less than 20ns.
Minimum Hi voltage level is 2.7V. Low level is
less than 0.8V. The frequency of the external Sync
signal needs to be greater than 445 KHz.
A rising edge on the SYNC pin forces a reset of
the oscillator. The upper DMOS is switched off
immediately if it is not already off. 250nS later the
upper DMOS turns on connecting SW to V
IN
.
BS 1
2
3
4
5
6
7
8
IN
SW
GND
SYNC
EN
COMP
FB
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
4
Applications Information
Bootstrap Capacitor C6
This bypasses the upper switch gate drive. Its
value should be > 4.7nF. For simplicity of design
this capacitor can be the same value as
Compensation cap C3.
Compensation Capacitor C3
This is the system compensation cap that is in
series with R3. Using a ceramic 10nF, 50V, X7R
capacitor allows it to match C5.
Auxiliary Compensation Capacitor C6
This is the system compensation cap that connects
between the COMP and GND pin. This capacitor
rolls off the high frequency noise and gain that can
cause duty cycle jitter. On well laid out boards
using low ESR Output capacitor (C2) C6 may not
be necessary. It 3DB frequency is set by
1/ (R3 X C6). For R3=10K and C6=100pF the
cut-off frequency is 159KHz which filters out the
400KHz switching noise and yet is above the GBW
target of 10KHz to 80KHz Use a ceramic 100pF,
50V, X7 capacitor.
Compensation Resistor R3
The loop compensation gain is directly proportional
to R3's value. The higher it's value the higher the
gain. Calculation of its value is discussed in detail
in the Loop Compensation section. Refer Table 4
for recommended values that accompany a
surface mount ceramic and special polymer output
capacitor.
Feedback Divider Resistors R2, R1
The Output voltage is set by R2 and R3:
V
OUT
= 1.22V
[
1 + (R2 / R1)]
The maximum recommended value of R1 is
100K . Too high an impedance can make the
Feedback node prone to noise injection particularly
if unshielded inductors are used. 10K is a good
standard value.
Input Bypass Capacitor C1
C1 is the bulk supply capacitor whose value should
be
10uF. The capacitor can be electrolytic,
tantalum or ceramic. However since it absorbs the
input switching current it requires an adequate
ripple current rating. Its RMS current rating should
be greater than approximately 1/2 of the output
current.
For insuring stable operation C1 should be placed
as close to the IC as possible. Alternately a
smaller high quality ceramic 0.1F capacitor may
be placed closer to the IC and the bulk C1 placed
further away. However if using this technique
some caution is needed if the bulk C1 is also a
high quality ceramic capacitor. Large voltage
excursions caused by resonant energy oscillation
between the two is possible.
Schottky Catch Diode D1
D1 supplies most of the current to inductor L1
when V
SW
is low. The lower the forward Schottky
voltage drop (V
SCH
) the higher the regulator
efficiency.
Tables 2 provides the Schottky part numbers
based on the maximum input voltage and current
rating. Table 3 lists manufacturer's websites.
D1's maximum reverse voltage rating should be
greater than the maximum input voltage V
IN
(Max).
The diode's average current rating must be above
the average load current:
I
DIODE
(AVG) = I
LOAD
X [V
IN
(V
OUT
+V
SCH
)] /V
IN
Example:
V
IN
= 12V, V
OUT
= 3.3V, I
LOAD
= 1.2A, V
SCH
=0.5V.
I
DIODE
(AVG) = 1.2A X [12-(3.3+0.5)] / 12V
= 0.82A
In this case a 1A diode can be used.
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
5
Applications Information Continued
Table 2: Diode Selection Guide
V
IN
(Max) 1A Diodes
2A Diodes
15V
10BQ15 30BQ15
20V
1N5817
B120
SS12
B220
SK23
SR22
30V
1N5818
B130
MBRS130
SS13
20BQ030
B230
SK23
SR23
SS23
Table 3: Schottky Diode Manufacturers
Vendor Web
Site
Diodes, Inc.
www.diodes.com
Fairchild Semiconductor
www.fairchildsemi.com
General Semiconductor
www.gensemi.com
International Rectifier
www.irf.com
On Semiconductor
www.onsemi.com
Pan Jit International
www.panjit.com.tw
Inductor L1
Optimal inductor selection involves trade-offs in
electrical value, current rating and mechanical
sizing.
Table 4 lists the recommended minimum inductor
values for common output voltage values. Table 5
Selection guide lists inductors by manufacturer,
electrical value, maximum output current, DC
resistance, core type, core material and
mechanical sizing.
The Maximum current rating of the inductor should
be above the peak operating current:
I
PEAK
= I
LOAD
+ (V
OUT
)(V
IN
-V
OUT
)
2(L)(F)(V
IN
)
Example: V
IN
=12V V
OUT
=3.3V, L=15H, I
LOAD
=1.2A
I
PEAK
= 1.6 + (3.3)(12-3.3)
2(15u)(380KHz)(12)
I
PEAK
= 1.809A
Using Table 5 select a 15H inductor with a Max
I
DC
rating of > 1.809A.
Output Capacitor - C2
The selection of the output capacitor is the most
critical component of a switching regulator. Its
electrical value and equivalent series resistance
(ESR) directly affect:
System stability
Loop compensation components R3
and C3
Output ripple voltage
Moreover C2 is frequently the most expensive
component of a switching regulator.
Figures 3 and 4 along with Table 4 are schematics
for two C2 components that have low ESR value.
Table IV. Recommended components for standard output voltages
V
OUT
R2
L1
minimum
1.22V
0 6.8H
1.5V
2.32K 6.8H
1.8V
4.75K 10H
2.5V
10.5K 10H
3.3V
16.9K 15H
5.0V
30.9K 22H
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
6
Figure 3:
ZA3020
with Murata 22F / 10V Ceramic Output
IN
BS
SW
FB
COMP
GND
EN
SYNC
L1
15H
D1
R2
10.5K
R1
10K
C2
22F/10V
Ceramic
C3
22
nF
R3
10K
INPUT
4.75 to 25V
C1
10F/35V
OPEN
C5
10nF
OUTPUT
2.5V/3A
NOT USED
ZA3020
C6
100pF
Figure 4:
ZA3020
with Panasonic 47F / 6.3V Special Polymer Output Capacitor
IN
BS
SW
FB
COMP
GND
EN
SYNC
L1
15H
D1
R2
10.5K
R1
10K
C2
47F/6.3V
Panasonic SP
C3
22
nF
R3
4.99K
INPUT
4.75 to 25V
C1
10F/50V
OPEN
C5
10nF
OUTPUT
2.5V/3A
NOT USED
ZA3020
C6
100pF
Note 1: For V
OUT
<2.5V R3 = 4.7K
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
7
Table 5. Inductor Selection Guide
Vendor/Model
Value
(H)
Max
I
DC
(A)
Max
DCR
( )
Core
Type
Core
Material
Package Dimensions (mm)
W
L
H
Sumida
CR75
10
2.3
0.070
Open
Ferrite
7.0 7.8 5.5
CR75
15
1.8
0.090
Open
Ferrite
7.0 7.8 5.5
CR75
22
1.5
0.110
Open
Ferrite
7.0 7.8 5.5
CDH74
10
2.75
0.056
Open
Ferrite
7.3 8.0 5.2
CDH74
15
2.1
0.083
Open
Ferrite
7.3 8.0 5.2
CDH74
22
1.7
0.130
Open
Ferrite
7.3 8.0 5.2
CDRH5D28
6.8
1.6
0.053
Shielded
Ferrite
5.5 5.7 5.5
CDRH5D28
10
1.3
0.065
Shielded
Ferrite
5.5 5.7 5.5
CDRH5D28
15
1.1
0.103
Shielded
Ferrite
5.5 5.7 5.5
CDRH6D28
6.8
2.3
0.031
Shielded
Ferrite
6.7 6.7 3.0
CDRH6D28
10
1.7
0.065
Shielded
Ferrite
6.7 6.7 3.0
CDRH6D28
15
1.6
0.057
Shielded
Ferrite
6.7 6.7 3.0
CDRH6D28
22
1.3
0.096
Shielded
Ferrite
6.7 6.7 3.0
CDRH6D38
6.8
2.3
0.031
Shielded
Ferrite
6.7 6.7 4.0
CDRH6D38
10
2.0
0.038
Shielded
Ferrite
6.7 6.7 4.0
CDRH6D38
15
1.6
0.057
Shielded
Ferrite
6.7 6.7 4.0
CDRH6D38
22
1.3
0.096
Shielded
Ferrite
6.7 6.7 4.0
CDRH104R
6.8
4.8
0.027
Shielded
Ferrite
10.1 10.0 3.0
CDRH104R
10
4.4
0.035
Shielded
Ferrite
10.1 10.0 3.0
CDRH104R
15
3.6
0.050
Shielded
Ferrite
10.1 10.0 3.0
CDRH104R
22
2.9
0.073
Shielded
Ferrite
10.1 10.0 3.0
Toko
D53LC Type A
6.8
2.01
0.068
Shielded
Ferrite
5.0 5.0 3.0
D53LC Type A
10
1.77
0.090
Shielded
Ferrite
5.0 5.0 3.0
D53LC Type A
15
1.40
0.142
Shielded
Ferrite
5.0 5.0 3.0
D53LC Type A
22
1.15
0.208
Shielded
Ferrite
5.0 5.0 3.0
D75C
6.8
1.79
0.050
Shielded
Ferrite
7.6 7.6 5.1
D75C
10
1.63
0.055
Shielded
Ferrite
7.6 7.6 5.1
D75C
15
1.33
0.081
Shielded
Ferrite
7.6 7.6 5.1
D75C
22
1.09
0.115
Shielded
Ferrite
7.6 7.6 5.1
D104C
10
4.3
0.0265
Shielded
Ferrite
10.0 10.0 4.3
D104C
16
3.3
0.0492
Shielded
Ferrite
10.0 10.0 4.3
D104C
22
2.5
0.0265
Shielded
Ferrite
10.0 10.0 4.3
D10FL
10
2.26
0.051
Open
Ferrite
9.7
11.5
4.0
D10FL
15
2.00
0.066
Open
Ferrite
9.7
11.5
4.0
D10FL
22
1.83
0.100
Open
Ferrite
9.7
11.5
4.0
Coilcraft
DO3308
10
2.4
0.030
Open
Ferrite
9.4
13.0
3.0
DO3308
15
2.0
0.040
Open
Ferrite
9.4
13.0
3.0
DO3308
22
1.6
0.050
Open
Ferrite
9.4
13.0
3.0
DO3316
10
3.8
0.030
Open
Ferrite
9.4
13.0
5.1
DO3316
15
3.0
0.040
Open
Ferrite
9.4
13.0
5.1
DO3316
22
2.6
0.050
Open
Ferrite
9.4
13.0
5.1
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.5 2003-04-22 www.vimicro.com
8
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
ZA3020 Rev. 3.
5 2003-04-22 www.vimicro.com
9
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+
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DC IN
ZA3020 DC-DC
R? + R02
-
(V)
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Packaging
SOIC8
NOTE:
1) Control dimension is in inches. Dimension in bracket is millimeters.
2) Heat Slug Option Only (N Package)
0.016(0.410)
0.050(1.270)
0
o
-8
o
DETAIL "A"
0.011(0.280)
0.020(0.508)
x 45
o
SEE DETAIL
0.0075(0.191)
0.0098(0.249)
0.229(5.820)
0.244(6.200)
SEATING PLANE
0.001(0.030)
0.004(0.101)
0.189(4.800)
0.197(5.004)
0.053(1.350)
0.068(1.730)
0.049(1.250)
0.060(1.524)
0.150(3.810)
0.157(4.000)
PIN 1 IDENT.
0.050(1.270)BSC
0.013(0.330)
0.020(0.508)
ZA3020
2A Step-Down, PWM, Switch-Mode
DC-DC Regulators
Notice:
Vimicro Corporation believes the information in this document to be accurate and reliable. However, it is subject
to change without notice. Please Contact the factory for current specifications No Responsibility is assumed by Vimicro
Corporation for its use or fit to any application, nor for infringement of patent or rights of third parties.
ZA3020 Rev. 3.
5
VIMICRO Corporation
2003-4-
22
4/F T2-B Building, South District, High-Tech Industrial Park Shenzhen, Guangdong P.R.C.
2003 VIMICRO Corp.
Tel:+86-755-26719818 Fax:+86-755-26719539 Web:www.Vimicro.com
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