Modulating Regulators. XR-2527A Datasheet

XR-2527A Regulators. Datasheet pdf. Equivalent


EXAR XR-2527A
XR·1525A/2525A/3525A
XR·1527A/2527A/3527A
Pulse-Width Modulating Regulators
GENERAL DESCRIPTION
The XR-1525A11527A is a series of monolithic inte-
grated circuits that contain all of the control circuitry
necessary for a pulse-width modulating regulator. In-
cluded in the 16-Pin dual-in-line package is a voltage
reference, an error amplifier, a pulse-width modulator,
an oscillator, under-voltage lockout, soft-start circuitry,
and output drivers.
FUNCTIONAL BLOCK DIAGRAM
INV
INPUT
NON·Ir-;V
INPUT
SYNC
The XR-1525A12525A13525A series features NOR logic,
giving a LOW output for an OFF state. The XR-1527AI
2525A13527A series features OR logic, giving a HIGH
output for an OFF state.
FEATURES
8V to 35V Operation
5.1 V Reference Trimmed to ± 1%
100 Hz to 500 kHz Oscillator Range
Separate Oscillator Sync Terminal
Adjustable Deadtime Control
Internal Soft-Start
Input Under-voltage Lockout
Latching PWM to Prevent Double Pulsing
Dual Source/Sink Output Drivers
Capable of Over 200 mA
Power·FET Drive Capability
APPLICATIONS
OSCILLATOR
OUTPUT
CT
RT
DISCHARGE
SOFT·START
ORDERING INFORMATION
Part Number
XR-1525A127M
XR-2525A127AN
XR-2525A127AP
XR-3525A127CN
XR-3525A127CP
Package
Ceramic
Ceramic
Plastic
Ceramic
Plastic
Operating Temperature
-55°C to +125°C
- 25°C to + 85°C
- 25°C to + 85°C
O°C to + 70°C
O°C to + 70°C
Power Control Systems
Switching Regulators
Industrial Controls
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (+ VIN)
+40V
Collector Supply Voltage (Vc)
+40V
Logic Inputs
- 0.3V to 5.5V
Analog Inputs
Output Current, Source or Sink
- 0.3V to + VIN
500 mA
Reference Output Current
50 mA
Oscillator Charging Current
5 mA
Power Dissipation
Ceramic Package
1000 mW
Derate above TA = + 25°C
8.0 mW/oC
Plastic Package
625 mW
Derate above TA = + 25°C
5.0 mW/oC
Operating Junction Temperature (TJ)
+ 150°C
Storage Temperature Range
- 65°C to + 150°C
SYSTEM DESCRIPTION
The on-chip 5.1-volt reference is trimmed to ± 1% ini-
tial accuracy, and the common-mode input range of the
error amplifier is extended to include the reference
voltage. Deadtime is adjustable with a single external
resistor. A sync input to the oscillator allows multiple
units to be slaved together, or a single unit to be syn-
chronized to an external clock. A positive-going signal
applied to the shutdoown pin provides instantaneous
turnoff of the outputs. The under-voltage lockout cir-
cuitry keeps the output drivers off, and the soft-start ca-
pacitor discharged, for an input voltage below the re-
quired value. The latch on the PWM comparator in-
sures the outputs are active only once per oscillator
period, thereby eliminating any double pulsing. The
latch is reset with each clock pulse.
The output drivers are totem-pole designs capable of
sinking and sourcing over 200 mA.
5-140


XR-2527A Datasheet
Recommendation XR-2527A Datasheet
Part XR-2527A
Description Pulse-Width Modulating Regulators
Feature XR-2527A; XR·1525A/2525A/3525A XR·1527A/2527A/3527A Pulse-Width Modulating Regulators GENERAL DESCRIPTION Th.
Manufacture EXAR
Datasheet
Download XR-2527A Datasheet




EXAR XR-2527A
XR·1527 A/2527 A/3527 A
XR·1525A/2525A/3525A
ELECTRICAL CHARACTERISTICS
= =Test Conditions: VIN + 20V, TJ Full operating temperature range, unless otherwise specified.
XR-1525A12525A
XR-1527Al2527A
XR-3525A
XR-3527A
PARAMETERS
MIN TYP MAX MIN TYP MAX UNIT
CONDITIONS
VOLTAGE REFERENCE SECTION
Output Voltage
Line Regulation
Load Regulation
Temperature Stability (2)
Total Output Variation (2)
Output Short Circuit
Current
Output Noise Voltage (2)
Long Term Stability (2)
5.05 5.10 5.15 5.00 5.10 5.20 V TJ = 25°C
10 20
10 20
mV VIN = BV to 35V
20 50
20 50
mV IL = 0 to 20 mA
20 50
20 50
mV TJ = Full Operating Range
5.00
5.20 4.95
5.25 V Line, Load and Temperature
BO 100
BO 100
mA TJ = 25°C, Vref = OV
40 200
20 50
40 200 J.LV rms TJ = 25°C, 10 Hz s f s 10 kHz
20 50 mV/kHR TJ = 125°C
OSCILLATOR SECTION (Note 3)
Initial Accuracy (2,3)
±2 ±6
±2 ±6
Temperature Stability (2)
±3 ±6
±3 ±6
Input Voltage Stability (2,3)
±0.3 ±1
±1 ±2
Minimum Frequency
100 100
Maximum Frequency
400
400
Current Mirror
1.7 2.0 2.2 1.7 2.0 2.2
Clock Amplitude (2,3)
3.0 3.5
3.0 3.5
Clock Pulse Width (2,3)
0.3 0.5 1.0 0.3 0.5 1.0
Sync Threshold
1.2 2.0 2.B 1.2 2.0 2.B
Sync Input Current
1.0 2.5
1.0 2.5
%
%
%
Hz
kHz
mA
V
J.Lsec
V
mA
TJ = 25°C, f = 40 kHz
TJ = Full Operating Range
VIN = BV to 35V
RT = 150 kO, Cr = 0.1 J.LF
RT = 2 kO, CT = 1 nF
IRT = 2 mA
TJ = 25°C, RD = 00
Sync Voltage = 3.5V
ERROR AMPLIFIER SECTION (VCM = 5.1V)
Input Offset Voltage
0.5 5.0
2 10
Input Bias Current
1 10
1 10
Input Offset Current
11
DC Open·Loop Gain
60 75
60 75
Gain Bandwidth Product (2)
1
2
12
Output Low Voltage
0.2 0.5
0.2 0.5
Output High Voltage
3.B 5.6
3.B 5.6
Common·Mode Rejection
60 75
60 75
Ratio
Supply Voltage Rejection
50 60
50 60
Ratio
mV
J.LA
J.LA
dB
MHz
V
V
dB
dB
RL ~ 10 MO
TJ = 25°C
VCM = 1.5V to 5.2V
VIN = BV to 35V
PULSE-WIDTH MODULATING COMPARATOR
Minimum Duty Cycle
Maximum Duty Cycle
Input Threshold (3)
Input Threshold (3)
Input Bias Current (2)
00
45 49
45 49
0.6 0.9
0.6 0.9
3.3 3.6
3.3 3.6
0.05 1.0
0.05 1.0
SOFT-START SECTION
Soft-Start Current
Soft-Start Voltage
Shutdown Input Current
25 50 BO 25 50 BO
0.4 0.6
0.4 0.6
0.4 1.0
0.4 1.0
OUTPUT DRIVERS (Each Output) Vc = 20V
Output Low Voltage
Output Low Voltage
Output High Voltage
Output High Voltage
Under-voltage Lockout
Collector Leakage (4)
Rise Time (2)
Fall Time (2)
Shutdown Delay (2)
0.2 0.4
0.2 0.4
1.0 2.0
1.0 2.0
1B 19
1B 19
17 1B
17 1B
6
7
B6
7
B
200 200
100 600
100 600
50 300
50 300
0.2 0.5
0.2 0.5
TOTAL STANDBY CURRENT
%
%
V Zero Duty Cycle
V Maximum Duty Cycle
J.LA
J.LA Vshutdown = OV
V Vshutdown = 2V
mA Vshutdown = 2.5V
V
V
V
V
V
J.LA
nsec
nsec
J.Lsec
Isink = 20 mA
Isink = 100 mA
Isource = 20 mA
Isource = 100 mA
Vcomp and VSS = High
Vc = 35V
TJ = 25°C, CL = 1 nF
TJ = 25°C, CL = 1 nF
VSD = 3V, Cs = 0, TJ = 25°C
Supply Current
14 20
14 20
mA VIN = 35V
Note 2: These parameters, although guaranteed over the recommended operating conditions, are not 100% tested in production.
Note 3: Tested at f = 40 kHz (RT = 3.6 kO, CT = 0.01 J.LF, RD = 00).
Note 4: Applies to XR-1525A12525A13525A only, due to polarity of output pulses.
5-141



EXAR XR-2527A
XR·1525A/2525A/3525A
XR·1527 A/2527 A/3527 A
PRINCIPLES OF OPERATION
The different control blocks within the XR-1525AJ1527A
function as follows:
Voltage Reference Section
The internal voltage reference circuit of the XR-1525AJ
1527A is based on the well-known "band-gap" refer-
ence, with a nominal output voltage of 5.1 volts, inter-
nally trimmed to ± 1% accuracy. It is short circuit pro-
tected and is capable of providing up to 20 mA of
reference current. A simplified circuit schematic is
shown in Figure 7.
Oscillator Section
The sawtooth oscillator derives its frequency from an
external timing resistor/capacitor pair. The timing resis-
tor, RT, determines the charging current into the timing
capacitor, Cr. The magnitude of this current is approxi-
mately given by:
Vref - 2VBE 3.7V
RT Rr
where RT may range from 2 kO to 150 kO. In general,
temperature stability is maximized with lower values of
Rr. The current source charging CT creates a linear
ramp voltage which is compared to fixed thresholds
within. When the capacitor voltage reaches + 3.3 volts,
the oscillator output (Pin 4) goes high, turning ON the
discharge transistor. The capacitor is discharged
through the deadtime resistor, RO. When the voltage on
CT falls to + 1.0 volt, the oscillator output goes low, the
discharge transistor is turned OFF, and the capacitor is
charged through the constant current source as an-
other cycle starts. With large values of RO (5000, maxi-
mum), deadtime is increased. The actual operating fre-
quency is thus a function of the charge and discharge
times. Figure 2 shows how charge time is related to RT
and Cr, with RO = 00. Oeadtime is a function of RO
and Cr, and can vary between 0.5 to 7 Ilsec, with RO =
00, as shown in Figure 3. The equivalent circuit sche-
matic of the oscillator section is shown in Figure 8.
A unit can be synchronized to an external source by se-
lecting its free-running oscillator period to be 10%
longer than the period of the external source. A
positive-going pulse of at least 300 nsec wide should be
applied to the sync terminal for reliable triggering; how-
ever, it should not exceed the free-running pulse width
by more than 200 nsec. The amplifier of the pulse
should be kept between 2 and 5 volts. Multiple units
can be synchronized to each other by connecting all CT
pins, and oscillator output pins together; RT pins and
discharge pins on slave oscillators must be left open.
Error Amplifier
The error amplifier of the XR-1525AJ1527A is a differen-
tial input transconductance amplifier. Its common-
mode range covers the reference voltage. Its open-loop
gain, typically 75 dB, can be reduced by a load resistor
on Pin 9. To ensure proper operation, the output load
should be limited to 50 kO or greater. An equivalent cir-
cuit schematic of the error amplifier is shown in Figure 9.
Soft-Start Circuitry
The soft-start fun'ction is provided to achieve controlled
turn-on of the pulse-width modulator. When power is
applied to the device, the external capacitor, Csoft-
start, on Pin 8 is charged by a 50 IlA constant current
source. The ramp voltage appearing on this capacitor
is fed into the pulse-width modulator, which gradually
increases its output duty cycle from zero to the pre-
scribed value. When the shutdown terminal is raised to
a positive value, an internal transistor turns ON, and
discharges the capacitor, CS, causing the PWM to turn
OFF. When the shutdown terminal is open or pulled low,
the transistor turns OFF, and Cs begins charging as be-
fore. The turn-on time (time required to charge Cs to
+ 2.7 volts) can be approximated as:
TC (msec) = 54 Cs
where Cs is in IlF.
Output Section
The output drivers of the XR-1525AJ1527A are totem-
pole designs capable of sinking and sourcing 200 mA.
The low source impedance in the high or low states pro-
vides ideal interfaCing with bipolar as well as FET
power transistors. Either push-pull or single-ended out-
put configurations are possible with separate collector
supply terminals. The equivalent schematic of the out-
put drivers is shown in Figure 10.
RECOMMENDED OPERATING CONDITIONS
Note 1: Range over which the device is functional
and parameter limits are guaranteed.
Collector Supply Voltage (Vc)
+ 4.5V to + 35V
Sink/Source Load Current
(Steady State)
Sink/Source Load Current (Peak)
Reference Load Current
o to 100 mA
o to 400 mA
o to 20 mA
Oscillator Frequency Range
100 Hz to 400 kHz
Oscillator Timing Resistor
2 kO to 150 kO
Oscillator Timing Capacitor
Oeadtime Resistor Range
0.001 IlF to 0.1 IlF
o to 5000
5-142





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