February 2, 2004 V5
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! Synchronous step-down DC/DC converter
with built-in LDO regulator plus voltage detector
! Step-down DC/DC converter's output connected in parallel
with LDO regulator
!
!
!
!
SOP-8 package for high current
Small-footprint
Output Current
(DC/DC : 800mA, VR : 400mA)
! APPLICATIONS
" CD-R / RW, DVD
" HDD
" PDAs, portable communication modem
" Cellular phones
" Palmtop computers
" Cameras, video recorders
Ceramic capacitor compatible (Low ESR capacitors)
! GENERAL DESCRIPTION
! FEATURES
The XC9511 series consists of a step-down DC/DC converter and a
high-speed LDO regulator connected in parallel with the DC/DC
converter's output. A voltage detector is also built-in. Since the input
for the LDO voltage regulator block comes from the input power
supply, it is suited for use with various applications.
The DC/DC converter block incorporates a P-Channel driver transistor
and a synchronous N-Channel switching transistor. With an external
coil, diode and two capacitors, the XC9511 can deliver output currents
up to 800mA at efficiencies over 90%. The XC9511 is designed for
use with small ceramic capacitors.
A choice of three switching frequencies are available, 300 kHz,
600 kHz, and 1.2 MHz.
Output voltage settings for the DC/DC and VR are set-up internally in
100mV steps within the range of 0.9V to 4.0V (± 2.0%). For the VD,
the range is of 0.9V to 5.0V (± 2.0%).
The soft start time of the series is internally set to 5ms. With the builtin U.V.L.O. (Under Voltage Lock Out) function, the internal P-channel
driver transistor is forced OFF when input voltage becomes 1.4 V or
lower.
Input Voltage Range :
2.4V ~ 6.0V
Load Capacitors :
Ceramic Capacitor Compatible
(Low ESR Capacitors)
VD Function :
Detects output voltage from the VDOUT pin
while sensing either VDD, DCOUT,
or VROUT internally.
Nch Open Drain Output
<DC/DC Converter>
Output Voltage Range : 0.9V ~ 4.0V (Accuracy ±2%)
Output Current :
800mA
Controls :
PWM Control
PWM, PWM / PFM Automatic
Switching External
Oscillation Frequency : 300kHz, 600kHz, 1.2MHz
<Regulator>
Output Voltage Range : 0.9V ~ 4.0V (Accuracy ±2%)
! TYPICAL APPLICATION CIRCUIT
Current Limit
600mA
Dropout Voltage :
160mV @ IOUT=200mA (VOUT=2.8V)
High Ripple Rejection
60dB @1kHz (VOUT=2.8V)
! TYPICAL PERFORMANCE CHARACTERISTICS
XC9511Axxxx
L
1
PGND
LX
8
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
100
DCOUT
VIN=5.0V, Topr=25OC, L:4.7uH(CDRH4D28C)
CIN:4.7uF(ceramic), CL1:10uF(ceramic), CL2:1uF(ceramic)
90
80
+
+
CIN1
Efficiency EFFI (%)
VROUT
+
CIN2
4
VDOUT
5
AGND
( )
C L2
+
C L1
SD
SOP-8 (TOP VIEW)
70
60
50
40
30
DC/DC Efficiency
(DCOUT:3.3V, 1.2MHz)
20
10
0
0.1
1
10
100
1000
DC/DC Output Current IDOUT
Semiconductor Ltd.
Data Sheet
1
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! PIN ASSIGNMENT
! PIN CONFIGURATION
PGND 1
8 LX
PVDD 2
7 DCOUT
AVDD 3
6 VROUT
VDOUT 4
5 AGND
SOP-8 (TOP VIEW)
PIN
NUMBER
PIN NAME
1
PGND
Power Ground
2
PVDD
Power Supply 1
3
AVDD
Power Supply 2
4
VDOUT
VD Output
5
AGND
Analog Ground
6
VROUT
VR Output
7
DCOUT
DC/DC Output
8
LX
Switch
FUNCTION
! SELECTION GUIDE
" Ordering Information
XC9511
123456
DESIGNATOR
The input for the voltage regulator block comes from VDD.
SYMBOL
1
23
DESCRIPTION
Control Methods and the VD Sense pin (See the chart below)
Setting voltage and specifications of each DC/DC, VR, and VD (Based on the internal standard)
Oscillation Frequency of DC/DC :
3
6
C
4
5
S
300kHz
600kHz
1.2MHz
Package Type :
SOP-8
Device Orientation :
6
R
L
Embossed Tape : Standard feed
Embossed Tape : Reverse feed
# Control Methods and VD SENSE Pin
SERIES
1
DC/DC CONTROL METHODS
VD
SENSE
PWM Control
DCOUT
VDD
A
B
XC9511
VROUT
C
D
E
F
PFM/PWM
Automatic Switch
VDD
DCOUT
VROUT
Semiconductor Ltd.
Data Sheet
2
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! PACKAGING INFORMATION
# SOP-8
! BLOCK DIAGRAM
PVDD
DCOUT
Phase
Compensation
+
+
logic
-
Vref with
soft start
Buffer,
Driver
Current Limit &
Feedback
PWM/PFM
Controller
LX
R amp Wave
Generator,
OSC
AVDD
PGND
-
VROUT
U.V.L.O
+
Current
Li mi t
+
VDOUT
+
-
Vref
-
SENSE
(VDD or DCOUT or VROUT)
Vref
AGND
* Diodes shown in the above circuits are protective diodes.
! ABSOLUTE MAXIMUM RATINGS
Ta=25OC
PARAMETER
SYMBOL
RATINGS
UNITS
AVDD Pin Voltage
PVDD pin Voltage
DCOUT Pin Voltage
VROUT Pin Voltage
VROUT Pin Current
VDOUT Pin Voltage
VDOUT Pin Current
LX Pin Voltage
LX Pin Current
SOP-8
Continuous Power Dissipation (*)
Operating Temperature Range
Storage Temperature Range
AVDD
PVDD
DCOUT
VROUT
IROUT
VDOUT
IVD
LX
ILX
Pd
- 0.3 ~ 6.5
AVDD - 0.3 ~ AVDD + 0.3
- 0.3 ~ AVDD + 0.3
- 0.3 ~ AVDD + 0.3
800
- 0.3 ~ AVDD + 0.3
50
- 0.3 ~ AVDD + 0.3
+ 1300
V
V
V
V
mA
V
mA
V
mA
mW
O
C
O
C
650
- 40 ~ + 85
- 55 ~ + 125
Topr
Tstg
(*) When PC board mounted.
Semiconductor Ltd.
Data Sheet
3
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! ELECTRICAL CHARACTERISTICS
XC9511xxxCSx
# Common Characteristics
PARAMETER
Topr=25OC
SYMBOL
CONDITIONS
MIN.
TYP.
MAX.
UNITS
TEST
CIRCUIT
Supply Current 1
IDD1
VIN=CE=DCOUT=5.0V
-
250
310
µΑ
1
Supply Current 2
IDD2
VIN=CE=5.0V, DCOUT=0V
-
300
360
µΑ
1
Input Voltage Range
VIN
2.4
-
6.0
V
-
MIN.
TYP.
MAX.
UNITS
TEST
CIRCUIT
1.470
1.500
1.530
V
3
1.02
1.20
1.38
MHz
3
100
-
-
%
4
-
-
0
%
4
21
30
38
%
3
1.00
1.40
1.78
V
3
-
0.5
1.0
Ω
5
-
0.5
0.9
Ω
3
# DC/DC Converter (1.5V product)
PARAMETER
SYMBOL
Output Voltage
DCOUT(E)
Oscillation Frequency
FOSC
Maximum Duty Ratio
MAXDUTY
Minimum Duty Ratio
PFM Duty Ratio
*XC9511D/E/F
U.V.L.O Voltage (note 1)
LX SW 'High' ON Resistance
(note 2)
MINDUTY
LX SW 'Low' ON Resistance
PFMDUTY
VUVLO
RLXH
RLXL
LX SW 'High' Leak Current
(note 11)
LX SW 'Low' Leak Current
(note 11)
Maximum Output Current
IMAX1
Current Limit (note 8)
ILIM1
Efficiency (note 3)
EFFI
CONDITIONS
Connected to the external components,
IDOUT=30mA
Connected to the external components,
IDOUT=10mA
DCOUT=0V
DCOUT=VIN
Connected to the external components,
No Load
Connected to the external components
DCOUT=0V, LX=VIN-0.05V
Connected to the external components,
VIN=5.0V
IleakH
VIN=LX=6.0V, CE=0V
-
0.05
1.00
µA
11
IleakL
VIN=6.0V, LX=CE=0V
-
0.05
1.00
µA
11
800
-
-
mA
3
1.0
1.1
-
A
6
Connected to the external components,
IDOUT=100mA
-
90
-
%
3
IDOUT=30mA
-40OC<Topr<85OC
-
±100
-
ppm/OC
3
2
5
10
mS
3
-
8
25
mS
10
Output Voltage
! DCOUT
Temperature Characteristics
(!Topr"DCOUT)
Soft Start Time
TSS
Latch Time (note 4, 9)
Tlat
Connected to the external components
Connected to the external components,
CE=0V"VIN, IDOUT=1mA
Connected to the external components,
VIN=CE=5.0V,
Short DCOUT by 1Ω resistor
# Regulator (3.3V product)
Topr=25OC
UNITS
TEST
CIRCUIT
3.366
V
2
-
mA
2
50
mV
2
PARAMETER
SYMBOL
CONDITIONS
MIN.
TYP.
MAX.
Output Voltage
VROUT(E)
IROUT=30mA
3.234
3.300
Maximum Output Current
400
-
Load Regulation
IMAX2
! VROUT
1mA<IROUT<100mA
-
15
Dropout Voltage 1 (note 5)
Vdif 1
IROUT=100mA
-
50
110
mV
2
Dropout Voltage 2
Vdif 2
! VROUT
IROUT=200mA
-
100
200
mV
2
IROUT=30mA
VROUT(T)+1V<VIN<6V
-
0.05
0.25
%/V
2
(!VIN"VROUT)
Line Regulation
Current Limit
ILIM2
VROUT=VROUT(E) x 0.9
480
600
-
mA
7
Short-Circuit Current
ISHORT
-
30
-
mA
7
Ripple Rejection Rate
PSRR
VROUT=VSS
VIN={VOUT(T) + 1.0} VDC + 0.5Vp-pAC
IROUT=30mA, f=1kHz
-
60
-
dB
12
IROUT=30mA
-40OC<Topr<85OC
-
±100
-
ppm / OC
2
Output Voltage
! VROUT
Temperature Characteristics
(!Topr"VROUT)
Semiconductor Ltd.
Data Sheet
4
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! ELECTRICAL CHARACTERISTICS (Continued)
# Detector (2.7V product)
Topr=25OC
PARAMETER
SYMBOL
CONDITIONS
MIN.
TYP.
MAX.
UNITS
TEST
CIRCUIT
Detect Voltage
VDF(E)
2.646
2.700
2.754
V
8
Hysteresis Range
VHYS
CE=0V
VHYS=[VDR(E) (note 10) - VDF(E)]
2
5
8
%
8
VDF(E) x 100
VD Output Current
IVD
VDOUT=0.5V, CE=0V
1
-
-
mA
9
Output Voltage
! VDF
-
±100
-
ppm/OC
8
Temperature Characteristics
(! Topr " VDF)
CE=0V,
-40OC<Topr<85OC
Test Conditions :
Unless otherwise stated;
DC/DC : VIN=3.6V [@ DCOUT:1.5V]
VR : VIN = 4.3V (VIN=VROUT(T) + 1.0V)
VD : VIN=6.0V
Common conditions for all test items : CE=VIN, MODE=0V
* VROUT(T) : Setting Output Voltage
note 1: Including hysteresis operating voltage range.
note 2: ON resistance (Ω)= 0.05 (V) / ILX (A)
note 3: EFFI = { ( Output Voltage x Output Current ) / ( Input Voltage x Input Current) } x 100
note 4: Time until it short-circuits DCOUT with GND through 1Ω of resistance from a state of operation
and is set to DCOUT=0V from current limit pulse generating.
note 5: Vdif = (VIN1 (note 6) - VROUT1 (note 7 ) )
note 6: VIN 1 = The input voltage when VROUT1 appears as input voltage is gradually decreased.
note 7: VROUT1 = A voltage equal to 98% of the output voltage whenever an amply stabilized IOUT {VROUT(T) + 1.0V} is input.
note 8: Current limit = When VIN is low, limit current may not be reached because of voltage falls caused
by ON resistance or serial resistance of coils.
note 9: Integral latch circuit=latch time may become longer and latch operation may not work when VIN is 3.0V or more.
note 10 : VDR(E) = VD release voltage
note 11 : When temperature is high, a current of approximately 5.0µA (maximum) may leak.
note 12 : When using the IC with a regulator output at almost no load, a capacitor should be placed as close as possible between
AVDD and AGND (CIN2), connected with low impedance. Please also see the recommended pattern layout
on page 13 for your reference. Should it not be possible to place the input capacitor nearby, the regulated output level
may increase up to the VDD level while the load of the DC/DC converter increases and the regulator output is at almost no load.
Semiconductor Ltd.
Data Sheet
5
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! TEST CIRCUITS
Circuit
1
Supply Current
Circuit
2
Output Voltage (VR), Load Regulation, Dropout Voltage,
Maximum Output Current
LX
8
LX
8
2
PVDD
DCOUT
7
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
3
AVDD
VROUT
6
4
VDOUT
AGND
5
4
VDOUT
AGND
5
1
PGND
1
DCOUT : VIN or GND
A
PGND
V
CIN :
4.7uF
(ceramic)
CIN : 1.0uF
(ceramic)
Circuit
3
V
Output Voltage (DC/DC), Oscillation Frequency,
Circuit
CL:1.0uF(ceramic,
2.2uF(ceramic,
4
IROUT
VROUT≧ 1.5V)
VROUT<1.5V)
Minimum Duty Cycle, Maximum Duty Cycle
U.V.L.O. Voltage, Soft start Time
Maximum Output Current, Efficiency,
(PFM Duty Cycle)
Probe
1
PGND
LX
8
Probe
1
PGND
LX
8
L
A
2
PVDD
DCOUT
7
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
3
AVDD
VROUT
6
4
VDOUT
AGND
5
4
VDOUT
AGND
5
V
IDOUT
V
V
CL:10uF
(ceramic)
CIN 1 2: 4.7uF
(ceramic)
Fosc
300kHz
600kHz
1.2MHz
Circuit
200Ω
5
CIN : 1.0uF
(ceramic)
L
22uH(CDRH6D38, SUMIDA)
10uH(CDRH5D28, SUMIDA)
4.7uH(CDRH4D28C, SUMIDA)
Lx ON Resistance
Circuit
6
Current Limit 1 (DC/DC)
Probe
PGND
A
LX
8
LX
8
2
PVDD
DCOUT
7
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
3
AVDD
VROUT
6
4
VDOUT
AGND
5
4
VDOUT
AGND
5
1
1
PGND
A
ILX
V
CIN : 1.0uF
(ceramic)
CIN : 4.7uF
(ceramic)
Semiconductor Ltd.
Data Sheet
6
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! TEST CIRCUITS (Continued)
Circuit
7
Current Limit 2 (VR), Short Current (VR)
1
PGND
LX
8
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
4
VDOUT
AGND
5
Circuit
8
Detect Voltage, Release Voltage (Hysteresis Range)
VD_SENSE *
(DCOUT or VROUT)
A
200k Ω
V
V
CIN : 4.7uF
(ceramic)
V
9
8
PVDD
PGND
DCOUT
7
3
AVDD
VROUT
6
4
VDOUT
AGND
5
VD Output Current
V
CIN : 1uF
(ceramic)
CL: 1.0uF
(ceramic)
CL : 1.0uF (ceramic, VROUT>1.5V)
2.2uF (ceramic, VROUT<1.5V)
Circuit
LX
2
1
* For the measurement of the VDD_Sense products,
the input voltage was controlled.
Circuit
10
Latch Time
VD_SENSE*
(DCOUT or VROUT)
L
1
A
PGND
LX
8
1
PGND
LX
8
2
PVDD
DCOUT
7
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
3
AVDD
VROUT
6
4
VDOUT
AGND
5
4
VDOUT
AGND
5
V
1Ω
CL:10uF
(ceramic)
CIN : 4.7uF
(ceramic)
CIN :1uF
(ceramic)
* For the measurement of the VDD_Sense products,
the input voltage was controlled.
Circuit
V
V
11
Off-Leak
12
PGND
LX
8
LX
8
PVDD
DCOUT
7
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
3
AVDD
VROUT
6
4
VDOUT
AGND
5
4
VDOUT
AGND
5
PGND
1
A
~
L
22uH(CDRH6D38,
600kHz
1.2MHz
10uH(CDRH5D28, SUMIDA)
4.7uH(CDRH4D28C, SUMIDA)
SUMIDA)
Ripple Rejection Rate
2
1
V
Circuit
Fosc
300kHz
V
V
IROUT
CIN : 4.7uF
(ceramic)
CIN : 1.0uF
(ceramic)
CL:1.0uF(ceramic,
2.2uF(ceramic,
VROUT >1.5V)
VROUT<1.5V)
Semiconductor Ltd.
Data Sheet
7
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! TYPICAL APPLICATION CIRCUIT
L
1
PGND
LX
8
2
PVDD
DCOUT
7
3
AVDD
VROUT
6
4
VDOUT
DCOUT
VROUT
+
+
CIN1
+
CIN2
AGND
5
( )
C L2
FOSC
L
1.2MHz
4.7µH (CDRH4D28C, SUMIDA)
600kHz
10µH (CDRH5D28, SUMIDA)
300kHz
22µH (CDRH6D28, SUMIDA)
SD : XB0ASB03A1BR (TOREX)
+
C L1
SD
SOP-8 (TOP VIEW)
CIN
: 4.7µF x 2 (ceramic, TAIYO-YUDEN)
CL1
: 10µF (ceramic, TAIYO-YUDEN)
CL2
:
1µF (ceramic, TAIYO-YUDEN), VROUT>1.5V
: 2.2µF (ceramic, TAIYO-YUDEN), VROUT<1.5V
The DC/DC converter of the XC9511 series automatically switches between synchronous / non-synchronous. The Schottky diode is not
normally needed. However, in cases where high efficiency is required when using the DC/DC converter during light load while in nonsynchronous operation, please connect a Schottky diode externally.
! OPERATIONAL EXPLANATION
The XC9511 series consists of a synchronous step-down DC/DC converter, a high speed LDO voltage regulator, and a voltage detector.
# DC/DC Converter
The series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase compensation circuit, output
voltage adjustment resistors, driver transistor, synchronous switch, current limiter circuit, U.V.L.O. circuit and others. The series ICs compare,
using the error amplifier, the voltage of the internal voltage reference source with the feedback voltage from the VOUT pin through split
resistors. Phase compensation is performed on the resulting error amplifier output, to input a signal to the PWM comparator to determine the
turn-on time during PWM operation. The PWM comparator compares, in terms of voltage level, the signal from the error amplifier with the ramp
wave from the ramp wave circuit, and delivers the resulting output to the buffer driver circuit to cause the Lx pin to output a switching duty cycle.
This process is continuously performed to ensure stable output voltage. The current feedback circuit monitors the P-channel MOS driver
transistor current for each switching operation, and modulates the error amplifier output signal to provide multiple feedback signals. This
enables a stable feedback loop even when a low ESR capacitor, such as a ceramic capacitor, is used, ensuring stable output voltage.
< Reference Voltage Source >
The reference voltage source provides the reference voltage to ensure stable output voltage of the DC/DC converter.
< Ramp Wave Circuit >
The ramp wave circuit determines switching frequency. The frequency is fixed internally and can be selected from 300kHz, 600 kHz and 1.2
MHz. Clock pulses generated in this circuit are used to produce ramp waveforms needed for PWM operation, and to synchronize all the internal
circuits.
< Error Amplifier >
The error amplifier is designed to monitor output voltage. The amplifier compares the reference voltage with the feedback voltage divided by the
internal split resistors. When a voltage lower than the reference voltage is fed back, the output voltage of the error amplifier increases. The
gain and frequency characteristics of the error amplifier output are fixed internally to deliver an optimized signal to the mixer.
< PWM/PFM >
The XC9511A to C series are PWM control, while the XC9511D to F series can be automatically switched to PWM/PFM control.
The PWM mode of the XC9511A to C series are controlled on a specified frequency from light loads through to heavy loads. Since the frequency
is specified, the composition of a noise filter etc. becomes easy. However, the efficiency at the time of the light load may become low.
The XC9511D to F series can switch to PWM/PFM automatic switching control. With the automatic PWM/PFM switching control function, the
series ICs are automatically switched from PWM control to PFM control mode under light load conditions. The series can not control only PFM
mode. If during light load conditions the coil current becomes discontinuous and on-time rate falls lower than 30%, the PFM circuit operates to
output a pulse with 30% of a fixed on-time rate from the Lx pin. During PFM operation with this fixed on-time rate, pulses are generated at
different frequencies according to conditions of the moment. This causes a reduction in the number of switching operations per unit of time,
resulting in efficiency improvement under light load conditions. However, since pulse output frequency is not constant, consideration should be
given if a noise filter or the like is needed. Necessary conditions for switching to PFM operation depend on input voltage, load current, coil value
and other factors.
Semiconductor Ltd.
Data Sheet
8
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! OPERATIONAL EXPLANATION (Continued)
< Synchronous / Non-synchronous >
The XC9511 series automatically switches between synchronous / non-synchronous according to the state of the DC/DC converter.
Highly efficient operations are achievable using the synchronous mode while the coil current is in a continuous state.
The series enters non-synchronous operation when the built-in Nch switching transistor for synchronous operation is shutdown which happens
when the load current becomes low and the operation changes to a discontinuous state.
The IC can operate without an external schottky diode because the parasitic diode in the Nch switching transistor provides the circuit's stepdown operation. However, since Vf of the parasitic diode is a high 0.6V, the efficiency level during non-synchronous operation shows a slight
decrease. Please use an external Schottky diode if high efficiency is required during light load current.
# Continuous Mode : Synchronous
# Discontinuous Mode : Non-Synchronous
ILmax
Coil Current
ILmax
ILmin
Coil Current
0mA
0mA
LX
W ave Form
LX
W ave Form
< Current Limit >
The current limiter circuit of the XC9511 series monitors the current flowing through the P-channel MOS driver transistor connected to the Lx
pin, and features a combination of the constant-current type current limit mode and the operation suspension mode.
1 When the driver current is greater than a specific level, the constant-current type current limit function operates to turn off the pulses from
the Lx pin at any given timing.
2 When the driver transistor is turned off, the limiter circuit is then released from the current limit detection state.
3 At the next pulse, the driver transistor is turned on. However, the transistor is immediately turned off in the case of an over current state.
4 When the over current state is eliminated, the IC resumes its normal operation.
The IC waits for the over current state to end by repeating the steps 1 through 3 . If an over current state continues for 8msec* and the
above three steps are repeatedly performed, the IC performs the function of latching the OFF state of the driver transistor, and goes into
operation suspension mode. Once the IC is in suspension mode, operations can be resumed by either turning the IC off via the CE pin, or by
restoring power to the VIN pin. The suspension mode does not mean a complete shutdown, but a state in which pulse output is suspended;
therefore, the internal circuitry remains in operation. The constant-current type current limit of the XC9511 series can be set at 1.1A.
.
Limit<8mS
*
Limit>8mS
*
Current Limit LEVEL
IDOUT
0mA
DCOUT
VSS
LX
CE
Restart
VIN
*1.2MHz, Typical
Semiconductor Ltd.
Data Sheet
9
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! OPERATIONAL EXPLANATION (Continued)
< U.V.L.O. Circuit>
When the VIN pin voltage becomes 1.4 V or lower, the P-channel output driver transistor is forced OFF to prevent false pulse output caused by
unstable operation of the internal circuitry. When the VIN pin voltage becomes 1.8 V or higher, switching operation takes place. By releasing
the U.V.L.O. function, the IC performs the soft start function to initiate output startup operation. The soft start function operates even when the
VIN pin voltage falls momentarily below the U.V.L.O. operating voltage. The U.V.L.O. circuit does not cause a complete shutdown of the IC, but
causes pulse output to be suspended; therefore, the internal circuitry remains in operation.
# High Speed LDO Voltage Regulator
The voltage regulator block of the XC9511 series consists of a reference voltage source, error amplifier, and current limiter circuit.
The voltage divided by split resistors is compared with the internal reference voltage by the error amplifier. The P-Channel MOSFET, which is
connected to the VROUT pin, is then driven by the subsequent output signal. The output voltage at the VROUT pin is controlled and stabilized
by a system of negative feedback. A stable output voltage is achievable even if used with low ESR capacitors as a phase compensation circuit
is built-in.
< Reference Voltage Source >
The reference voltage source provides the reference voltage to ensure stable output voltage of the regulator.
< Error Amplifier >
The error amplifier compares the reference voltage with the signal from VROUT, and the amplifier controls the output of the Pch driver transistor.
<Current Limit Circuit>
The voltage regulator block includes a combination of a constant current limiter circuit and a foldback circuit. The voltage regulator senses
output current of the built-in P channel output driver transistor inside. When the load current reaches the current limit level, the current limiter
circuit operates and the output voltage of the voltage regulator block drops. As a result of this drop in output voltage, the foldback circuit
operates, output voltage drops further and the load current decreases. When the VROUT and GND pin are shorted, the load current of about
30mA flows.
# Voltage Detector
The detector block of the XC9511 series detects output voltage from the VDOUT pin while sensing either VDD, DCOUT, or VROUT internally.
(N channel Open Drain Type)
Semiconductor Ltd.
Data Sheet
10
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! NOTES ON USE
" Application Information
1. The XC9511 series is designed for use with a ceramic output capacitor. If, however, the potential difference between dropout voltage or
output current is too large, a ceramic capacitor may fail to absorb the resulting high switching energy and oscillation could occur on the
output. If the input-output potential difference is large, connect an electrolytic capacitor in parallel to compensate for insufficient
capacitance.
2. Spike noise and ripple voltage arise in a switching regulator as with a DC/DC converter. These are greatly influenced by external
component selection, such as the coil inductance, capacitance values, and board layout of external components. Once the design has
been completed, verification with actual components should be done.
3. When the difference between VIN and VOUT is large in PWM control, very narrow pulses will be outputted, and there is the possibility
that some cycles may be skipped completely.
4. When the difference between VIN and VOUT is small, and the load current is heavy, very wide pulses will be outputted and there is the
possibility that some cycles may be skipped completely: in this case, the Lx pin may not go low at all.
# DC/DC Waveform (3.3V, 1.2MHz)
CH1:LX
CH1:LX
CH2:DCOUT
CH2:DCOUT
Off-set Voltage:3.3V
Off-set Voltage:3.3V
VIN=3.7V, IDOUT=100mA
VIN=3.5V, IDOUT=100mA
<External Components>
L: 4.7µH (CDRH4D28C, SUMIDA)
CIN: 4.7µF (ceramic)
CL: 10µF (ceramic)
<External Components>
L: 4.7µH (CDRH4D28C, SUMIDA)
CIN: 4.7µF (ceramic)
CL: 10µF (ceramic)
5. The IC's DC/DC converter operates in synchronous mode when the coil current is in a continuous state and non-synchronous mode when
the coil current is in a discontinuous state. In order to maintain the load current value when synchronous switches to non-synchronous and
vise versa, a ripple voltage may increase because of the repetition of switching between synchronous and non-synchronous. When this
state continues, the increase in the ripple voltage stops. To reduce the ripple voltage, please increase the load capacitance value or use a
schottky diode externally. When the current used becomes close to the value of the load current when synchronous switches to nonsynchronous and vise versa, the switching current value can be changed by changing the coil inductance value. In case changes to coil
inductance are to values other than the recommended coil inductance values, verification with actual components should be done.
Ics=
(VIN - DCOUT) x OnDuty / (L x Fosc)
Ics : Switching current from synchronous rectification to non-synchronous rectification
OnDuty : OnDuty ratio of P-ch driver transistor (
step down ratio : DCOUT / VIN)
L : Coil inductance value
Fosc : Oscillation Frequency
IDOUT : The DC/DC load current
Semiconductor Ltd.
Data Sheet
11
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! NOTES ON USE (Continued)
" Application Information (Continued)
6. When the XC9511D to F series operate in PWM/PFM automatic switching control mode, the reverse current may become quite high
around the load current value when synchronous switches to non-synchronous and vise versa (also refer to no. 5 above). Under this
condition, switching synchronous rectification and non-synchronous rectification may be repeated because of the reverse current, and the
ripple voltage may be increased to 100mV or more. The reverse current is the current that flows in the PGND direction through the Nch
driver transistor from the coil. The conditions which cause this operation are as follows.
PFM Duty < Step down ratio = DCOUT / VIN x 100 (%)
PFM Duty : 30% (TYP.)
The XC9511A to C series are recommended in cases where the load current value of the DC/DC converter is close to synchronous.
# DC/DC Waveform (1.8V, 600kHz) @ VIN=6.0V
CH1:LX
CH2:DCOUT
Off-set Voltage:1.8V
VIN=6.0V, IDOUT=50mA
<External Components>
L: 10µH (CDRH5D28, SUMIDA)
CIN: 4.7µF (ceramic)
CL: 10µF (ceramic)
Step down ratio : 1.8V / 6.0V =30% <PFM Duty 31%>
7. With the DC/DC converter of the IC, the peak current of the coil is controlled by the current limit circuit. Since the peak current increases
when dropout voltage or load current is high, current limit starts operating, and this can lead to instability. When peak current becomes
high, please adjust the coil inductance value and fully check the circuit operation. In addition, please calculate the peak current according
to the following formula:
Peak current : Ipk = (VIN - DCOUT) x OnDuty / (2 x L x Fosc) + IDOUT
8. When the peak current which exceeds limit current flows within the specified time, the built-in driver transistor is turned off (the integral
latch circuit). During the time until it detects limit current and before the built-in transistor can be turned off, the current for limit current
flows; therefore, care must be taken when selecting the rating for the coil or the Schottky diode.
9. When VIN is low, limit current may not be reached because of voltage falls caused by ON resistance or serial resistance of the coil.
10. In the integral latch circuit, latch time may become longer and latch operation may not work when VIN is 3.0V or more.
11. Use of the IC at voltages below the recommended voltage range may lead to instability.
12. This IC and the external components should be used within the stated absolute maximum ratings in order to prevent damage to the device.
13. When using IC with a regulator output at almost no load, a capacitor should be placed as close as possible between AVDD and AGND
(CIN2), connected with low impedance. Please also see the recommended pattern layout on page 13 for your reference. Should it not be
possible to place the input capacitor nearby, the regulated output level may increase up to the VDD level while the load of the DC/DC
converter increases and the regulator output is at almost no load.
Semiconductor Ltd.
Data Sheet
12
XC9511 Series
Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
Preliminary
! NOTES ON USE (Continued)
" Application Information (Continued)
14. Should the bi-directional load current of the synchronous DC/DC converter and the regulator become large, please be careful of the
power dissipation when in use. Please calculate power dissipation by using the following formula.
Pd=PdDC/DC + PdVR
PdDC/DC = IDOUT2 x RON
DC/DC power dissipation (when in synchronous operation) :
DCOUT (V)
VIN
VR power dissipation : PDVR = (VIN - VROUT) x IROUT
DC/DC
IDOUT (mA)
RON: ON resistance of the built-in driver transistor to the DC/DC ( = 0.5Ω <TYP.>)
VROUT (V)
VR
IROUT (mA)
RON=Rpon x PchOnDuty / 100
+ Rnon x (1 - PchOnDuty / 100)
# Instructions on Pattern Layout
1. In order to stabilize VIN's voltage level, we recommend that a by-pass capacitor (CIN) be connected as close as possible to the AVDD &
AGND pins. Should it not be possible to place the input capacitors nearby, the regulated output level may increase because of the switching
noise of the DC/DC converter.
2. Please mount each external component as close to the IC as possible.
3. Wire external components as close to the IC as possible and use thick, short connecting traces to reduce the circuit impedance.
4. Make sure that the PCB GND traces are as thick as possible, as variations in ground potential caused by high ground currents at the time of
switching may result in instability of the DC/DC converter and have adverse influence on the regulator output.
5. If using a Schottky diode, please connect the anode side to the AGND pin through CIN. Characteristic degradation caused by the noise may
occur depending on the arrangement of the Schottky diode.
6. Please use the AVDD and PVDD pins with the same electric potential.
<SOP-8 Recommended pattern layout>
CL1
PGND
L
SD
LX
+
PVDD
IC
VDOUT
+
DCOUT
VROUT
+
AGND
AVDD
CIN1
CL2
CIN2
( Through Hole to CIN1 )
( Through Hole to SD )
Semiconductor Ltd.
Data Sheet
13