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PDF APW8720B Data sheet ( Hoja de datos )
| Número de pieza | APW8720B | |
| Descripción | Single Buck Voltage Mode PWM Controller | |
| Fabricantes | ANPEC | |
| Logotipo |  |
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APW8720B
Single Buck Voltage Mode PWM Controller
Features
General Description
• Wide 5V to 12V Supply Voltage
The APW8720B is a voltage mode, fixed 300kHz switch-
• Power-On-Reset Monitoring on VCC
ing frequency, synchronous buck converter. The
• Excellent Output Voltage Regulations
APW8720B allows wide input voltage that is either a single
- 0.8V Internal Reference
5~12V or two supply voltage(s) for various applications. A
- ±1% Over-Temperature Range
power-on-reset (POR) circuit monitors the VCC supply
• Integrated Soft-Start
voltage to prevent wrong logic controls. A built-in soft-start
• Voltage Mode PWM Operation with External circuit prevents the output voltages from overshoot as
well as limits the input current. An internal 0.8V tempera-
Compensation
ture-compensated reference voltage with high accuracy
• Up to 90% Duty Ratio for Fast Transient Response is designed to meet the requirement of low output volt-
• Constant Switching Frequency
age applications. The APW8720B provides excellent out-
- 300kHz ±10%
put voltage regulations against load current variation.
• 9V Driver Voltage for BOOT Supply with Internal The controller’s over-current protection monitors the out-
Bootstrap Diode
put current by using the voltage drop across the RDS(ON) of
• Drive Dual Low Cost N-MOSFETs with Adaptive low-side MOSFET, eliminating the need for a current sens-
Dead-Time Control
ing resistor that features high efficiency and low cost. In
• 50% Under-Voltage Protection
• 125% Over-Voltage Protection
• Adjustable Over-Current Protection Threshold
- Using the R of Low-Side MOSFET
DS(ON)
addition, the APW8720B also integrates excellent protec-
tion functions: The over-voltage protection (OVP) , under-
voltage protection (UVP). OVP circuit which monitors the
FB voltage to prevent the PWM output from over-voltage,
and UVP circuit which monitors the FB voltage to prevent
• Shutdown Control by COMP
the PWM output from under-voltage or short-circuit.
• Power Good Monitoring (TDFN-10 3mmx3mm The APW8720B is available in SOP-8P and TDFN3x3-10
Package Only)
packages.
• SOP-8P and TDFN3x3-10 Packages
• Lead Free and Green Devices Available
(RoHS Compliant)
Simplified Application Circuit
Applications
• Graphic Cards
• DSL, Switch HUB
• Wireless Lan
• Notebook Computer
• Mother Board
• LCD Monitor/TV
OFF
ON
VCC
APW8720B
VCCBOOT
UGATE
COMP
PHASE
LGATE
FBGND
VIN
VOUT
ANPEC reserves the right to make changes to improve reliability or manufacturability without notice, and
advise customers to obtain the latest version of relevant information to verify before placing orders.
Copyright © ANPEC Electronics Corp.
Rev. A.5 - Mar., 2012
1
www.anpec.com.tw
Free Datasheet http://www.datasheet4u.com/
1 page  
APW8720B
Operating Waveforms
Refer to the typical application circuit. The test condition is VIN=12V, TA=25oC unless otherwise specified.
Power On
Power Off
Enable
Shutdown
Ω
Copyright © ANPEC Electronics Corp.
Rev. A.5 - Mar., 2012
5
www.anpec.com.tw
Free Datasheet http://www.datasheet4u.com/
5 Page 
APW8720B
Function Description
Power-On-Reset (POR)
The Power-On-Reset (POR) function of APW8720B con-
tinually monitors the input supply voltage (VCC) and en-
sures that the IC has sufficient supply voltage and can
work well. The POR function initiates a soft-start process
while the VCC voltage just exceeds the POR threshold;
the POR function also inhibits the operations of the IC
while the VCC voltage falls below the POR threshold.
Soft-Start
The APW8720B builds in a soft-start function about
1.5ms (Typ.) interval, which controls the output voltage
rising as well as limiting the current surge at the start-up.
During soft-start, an internal ramp voltage connected to
the one of the positive inputs of the error amplifier re-
places the reference voltage (0.8V typical) until the ramp
voltage reaches the reference voltage. The soft-start cir-
cuit interval is shown as figure 1. The UVP function en-
able delay is from t2 to t3.
Voltage(V)
POK Delay Time
VVCC
OCSET count completed
OCSET count start
(OCSET duratiom, t2-t1, less than 1.3ms)
VPOK
0.9xVREF
VOUT
t0 t1 t2 t3 t4
Time
Figure 1. Soft-Start Interval
Over-Current Protection of the PWM Converter
The over-current function protects the switching converter
against over-current or short-circuit conditions. The con-
troller senses the inductor current by detecting the drain-
to-source voltage which is the product of the inductor’s
current and the on-resistance of the low-side MOSFET
during it’s on-state. This method enhances the converter’s
efficiency and reduces cost by eliminating a current sens-
ing resistor required.
A resistor (ROCSET), connected from the LGATE/OCSET to
GND, programs the over-current trip level. Before the IC
initiates a soft-start process, an internal current source,
IOCSET (10µA typical), flowing through the ROCSET develops
a voltage (VROCSET) across the ROCSET. The device holds
VROCSET and stops the current source IOCSET during normal
operation. When the voltage across the low-side MOSFET
exceeds the V , the APW8720B turns off the high-
ROCSET
side and low-side MOSFET,and the device will enters
hiccup mode until the over-current phenomenon is
released.
For avoid large inductor current occurring in short circuit
before power on, the controller reduces internal current
source, Iocset, to half during soft start time.
It means that when APW8720B is in soft start interval, the
internal current source, Iocset, is only 5µA (typical).
The APW8720B has an internal OCP voltage, V
,
OCP_MAX
and the value is 0.35V (minimum). When the ROCSET x
IOCSET exceed 0.35V or the ROCSET is floating or not
connected, the V
will be the default value 0.35V. The
ROCSET
over current threshold would be 0.35V across low-side
MOSFET. The threshold of the valley inductor current-limit
is therefore given by:
ILIMIT
=
IOCSET × ROCSET
RDS(ON)(low − side)
For the over-current is never occurred in the normal oper-
ating load range, the variation of all parameters in the
above equation should be considered:
- The RDS(ON) of low-side MOSFET is varied by tempera-
ture and gate to source voltage. Users should deter-
mine the maximum R by using the manufacturer’s
DS(ON)
datasheet.
- The minimum IOCSET (9µA) and minimum ROCSET should
be used in the above equation.
- Note that the ILIMIT is the current flow through the low-
side MOSFET; ILIMIT must be greater than valley inductor
current which is output current minus the half of induc-
tor ripple current.
Copyright © ANPEC Electronics Corp.
Rev. A.5 - Mar., 2012
11
www.anpec.com.tw
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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