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D1067
DESCRIPTION
The DMS1067 is a monolithic step-down switch
mode converter with a built in internal power
MOSFET. It achieves 2A continuous output cur-
rent over a wide input supply range with excel-
lent load and line regulation.
The DMS1067 requires a minimum number of
readily available standard external components.
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 25µA of
supply current.
FEATURES
2A Output Current
0.22Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic Ca-
pacitors
Up to 95% Efficiency
25µA Shutdown Mode
Fixed 420KHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Wide 4.75 to 25V Operating Input Range
Output Adjustable from 1.22V to 21V
Programmable Under Voltage Lockout
APPLICATIONS
Distributed Power Systems
Battery Chargers
Pre-Regulator for Linear Regulators
PC Monitors
4.75 to 25
DMS1067
PACKAGE REFERENCE
Part number
DMS1067S
DMS1067P
Package
SOIC8
PDIP8
Temperature
–40°C to +125°C
–40°C to +125°C
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ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage (VIN)..................................... 27V
Switch Voltage (VSW)................ –1V to VIN + 1V
Bootstrap Voltage (VBS) ...Vsw-0.3V to VSW + 6V
Enable/UVLO Voltage (VEN)...........–0.3V to +6V
Comp Voltage (VCOMP) ...................–0.3V to +6V
Feedback Voltage (VFB) ................–0.3V to +6V
Junction Temperature ........................... +150°C
Lead Temperature ................................. +260°C
Storage Temperature.............. –65°C to +150°C
D1067
Recommended Operating Conditions(2)
Input Voltage (VIN) ......................... 4.75V to 25V
Operating Temperature...............–40°C to +125°C
Thermal Resistance(3) θJA θJC
SOIC8 .................................... 105..... 50... °C/W
PDIP8 ...................................... 95…...55.. °C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The device is not guaranteed to function outside of its
operating conditions.
3) Measured on approximately 1” square of 1 oz copper.
ELECTRICAL CHARACTERISTICS
VIN = 12V, VEN = 5V,TA = +25°C, unless otherwise noted.
Parameter
Condition
Feedback Voltage
Upper Switch-On Resistance
4.75V VIN 25V
Lower Switch-On Resistance
Upper Switch Leakage
Current Limit
VEN = 0V, VSW = 0V
Oscillator Frequency
Short Circuit Frequency
Maximum Duty Cycle
Minimum Duty Cycle
EN Shutdown Threshold Voltage
EN UVLO Threshold Rising
EN UVLO Threshold Hysteresis
Enable Pull-Up Current
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
VFB = 0V
VFB = 1.0V
VFB = 1.5V
ICC > 100µA
VEN Rising
VEN = 0V
VEN 0.4V
VEN 2.6V, VFB = 1.4V
Min
1.184
2.4
370
2.0
2.0
Typ
1.222
0.22
10
3.1
420
42
90
2.3
2.5
200
2
25
1.0
160
Max
1.258
10
470
0
2.5
3.0
50
1.5
Units
V
µA
A
KHz
KHz
%
%
V
V
mV
µA
µA
mA
°C
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D1067
PIN FUNCTIONS
Pin # Name Description
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-channel
1 BS MOSFET switch. Connect a 10nF or greater capacitor from SW to BS to power the
switch.
Power Input. IN supplies the power to the IC, as well as the step-down converter switch.
2 IN Drive In with a 4.75 to 25V power source. Bypass IN to GND with a suitably large capaci-
tor to eliminate noise on the input to the IC. See Input Capacitor.
3 SW Power Switching Output. SW is the switching node that supplies power to the output.
Connect the output LC filter from SW to the output load. Note that a capacitor is required
from SW to BS to power the high-side switch.
4 GND Ground.
5 FB Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a
resistive voltage divider from the output voltage. The feedback threshold is 1.222V. See
Setting the Output Voltage.
6 COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect
a series RC network from COMP to GND to compensate the regulation control loop. See
Compensation.
7 EN Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn
on the regulator, low to turn it off. For automatic startup, leave EN unconnected.
8 NC No Connect.
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D1067
OPERATION
The DMS1067 is a current-mode step-down
switch-mode regulator. It regulates input voltages
from 4.75V to 25V down to an output voltage as
low as 1.222V and is able to supply up to 2A of
load current. The DMS1067 uses current-mode
control to regulate the output voltage. The output
voltage is measured at FB through a resistive
voltage divider and amplified through the internal
error amplifier. The output current of the trans-
conductance error amplifier is presented at
COMP where a network compensates the regu-
lation control system. The voltage at COMP is
compared to the switch current measured inter-
nally to control the output voltage.
The converter uses an internal N-Channel
MOSFET switch to step down the input voltage
to the regulated output voltage. Since the
MOSFET requires a gate voltage greater than
the input voltage, a boost capacitor connected
between SW and BS drives the gate. The ca-
pacitor is internally charged while the switch is
off. An internal 10 switch from SW to GND is
used to ensure that SW is pulled to GND when
the switch is off to fully charge the BS capacitor.
42-450KHz
Figure 1 – Functional Block Diagram
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D1067
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive volt-
age divider from the output voltage to FB (see
Typical Application circuit on page 1). The volt-
age divider divides the output voltage down by
the ratio:
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
R2 can be as high as 100kQ, but a typical value
is 10k. Using that value, R1 is determined by:
For example, for a 3.3V output voltage, R2 is
10k, and R1 is 16.9k.
Inductor
The inductor is required to supply constant cur-
rent to the output load while being driven by the
switched input voltage. A larger value inductor
results in less ripple current that results in lower
output ripple voltage. However, the larger value
inductor has a larger physical size, higher series
resistance and/or lower saturation current.
Choose an inductor that does not saturate under
the worst-case load conditions. A good rule for
determining the inductance is to allow the peak-
to-peak ripple current in the inductor to be ap-
proximately 30% of the maximum load current.
Also, make sure that the peak inductor current
(the load current plus half the peak-to-peak in-
ductor ripple current) is below the 2.4A minimum
current limit.
The inductance value can be calculated by the
equation:
Where VIN is the input voltage, f is the switching
frequency, and Δl is the peak-to-peak inductor
ripple current.
Table 1 lists a number of suitable inductors from vari-
ous manufacturers.
Table 1—Inductor Selection Guide
Vendor/ Model Core
Core Ma- Package
Type
terial Dimensions
(mm)
W LH
Sumida
CR75
CDH74
CDRH5D28
CDRH5D28
CDRH6D28
CDRH104R
Open
Open
Shielded
Shielded
Shielded
Shielded
Ferrite 7.0 7.8 5.5
Ferrite 7.3 8.0 5.2
Ferrite 5.5 5.7 5.5
Ferrite 5.5 5.7 5.5
Ferrite 6.7 6.7 3.0
Ferrite 10.1 10.0 3.0
Toko
D53LC Type A Shielded
D75C
Shielded
D104C
Shielded
D10FL
Open
Ferrite 5.0 5.0 3.0
Ferrite 7.6 7.6 5.1
Ferrite 10.0 10.0 4.3
Ferrite 9.7 1.5 4.0
Coilcraft
DO3308
D03316
Open
Open
Ferrite 9.4
Ferrite 9.4
13.0 3.0
13.0 5.1
Input Capacitor
The input current to the step-down converter is dis-
continuous, and therefore an input capacitor C1 is
required to supply the AC current to the step-down
converter while maintaining the DC input voltage. A
low ESR capacitor is required to keep the noise at the
IC to a minimum. Ceramic capacitors are preferred,
but tantalum or low-ESR electrolytic capacitors may
also suffice.
The input capacitor value should be greater than
10uF. The capacitor can be electrolytic, tantalum or
ceramic. However, since it absorbs the input switch-
ing current it requires an adequate ripple current rat-
ing. Its RMS current rating should be greater than ap-
proximately 1/2 of the DC load current.
For insuring stable operation, C2 should be placed as
close to the IC as possible. Alternately a smaller high
quality ceramic 0.1 uF capacitor may be placed closer
to the IC and a larger capacitor placed further away. If
using this technique, it is recommended that the lar-
ger capacitor be a tantalum or electrolytic type. All
ceramic capacitors should be placed close to the
DMS1067.
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