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PDF KB3426 Data sheet ( Hoja de datos )
| Número de pieza | KB3426 | |
| Descripción | 800mA Synchronous Step-Down Regulator | |
| Fabricantes | Kingbor Technology | |
| Logotipo |  |
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Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
FEATURES
■ High Efficiency: Up to 96%
■ Very Low Quiescent Current: Only 20µA
www.DataSheDeut4rUin.cgomOperation
■ 800mA Output Current
■ 2.5V to 6.5V Input Voltage Range
■ 1.5MHz Constant Frequency Operation
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ 0.6V Reference Allows Low Output Voltages
■ Shutdown Mode Draws ) 1µA Supply Current
■ Current Mode Operation for Excellent Line and
Load Transient Response
■ Overtemperature Protected
■ Low Profile (1mm) SOT23-5 Package
APPLICATIONS
■ Cellular Telephones
■ Personal Information Appliances
■ Wireless and DSL Modems
■ Digital Still Cameras
■ MP3 Players
■ Portable Instruments
KB3426
1.5MHz, 800mA
Synchronous Step-Down
Regulator in SOT23-5
DESCRIPTION
The KB3426 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
version and fixed output voltages of 1.8V and 3.3V. Supply
current during operation is only 20µA and drops to )1µA
in shutdown. The 2.5V to 5.5V input voltage range makes
the KB3426 ideally suited for single Li-Ion battery-pow-
ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
Automatic Burst Mode operation increases efficiency at
light loads, further extending battery life.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feed-
back reference voltage. The KB3426 is available in a low
profile (1mm) SOT23-5 package.
TYPICAL APPLICATION
VIN
3.6V
TO 6.5V
+ CIN
4.7µF
Tan
4
VIN
4.7µH
3
SW
KB3426-3.3
15
RUN VOUT
GND
2
COUT
10µF
CER
VOUT
3.3V
800mA
Figure 1a. High Efficiency Step-Down Converter
95
VIN = 3.6V
90
85
VIN = 3.8V
80
VIN = 4.2V
75
70
65
60
0.1
VOUT = 3.3V
1 10 100
OUTPUT CURRENT (mA)
1000
Figure 1b. Efficiency vs Load Current
1
1 page  
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
TYPICAL PERFORMANCE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
KB3426
Start-Up from Shutdown
RUN
2V/DIV
VOUT
2V/DIV
www.DataSheet4U.com
ILOAD
500mA/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 800mA
40µs/DIV
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 0mA TO 800mA
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 50mA TO 800mA
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 100mA TO 800mA
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 200mA TO 800mA
PIN FUNCTIONS
RUN (Pin 1): Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
VIN (Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
VFB (Pin 5) (kB3426): Feedback Pin. Receives the feed-
back voltage from an external resistive divider across the
output.
VOUT (Pin 5) (kB3426-1.8/kB3426-3.3): Output Volt-
age Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal refer-
ence voltage.
5
5 Page 
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
KB3426
APPLICATIONS INFORMATION
The junction temperature, TJ, is given by:
TJ = TA + TR
where TA is the ambient temperature.
As an example, consider the KB3426 in dropout at an
input voltage of 2.7V, a load current of 800mA and an
www.DataaSmhebeti4eUn.tcotmemperature of 70°C. From the typical perfor-
mance graph of switch resistance, the RDS(ON) of the
P-channel switch at 70°C is approximately 0.521. There-
fore, power dissipated by the part is:
PD = ILOAD2 • RDS(ON) = 187.2mW
For the SOT-23 package, the eJA is 250°C/ W. Thus, the
junction temperature of the regulator is:
TJ = 70°C + (0.1872)(250) = 116.8°C
which is below the maximum junction temperature of
125°C.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance (RDS(ON)).
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to (6ILOAD • ESR), where ESR is the effective series
resistance of COUT. 6ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steady-
state value. During this recovery time VOUT can be moni-
tored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
A second, more severe transient is caused by switching in
loads with large (>1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25 • CLOAD).
Thus, a 10µF capacitor charging to 3.3V would require a
250µs rise time, limiting the charging current to about
130mA.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
KB3426. These items are also illustrated graphically in
Figures 5 and 6. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW
trace and the VIN trace should be kept short, direct and
wide.
2. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1/R2 must be con-
nected between the (+) plate of COUT and ground.
3. Does the (+) plate of CIN connect to VIN as closely as
possible? This capacitor provides the AC current to the
internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive
VFB node.
5. Keep the (–) plates of CIN and COUT as close as possible.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet KB3426.PDF ] | |
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