ETC PJ3800

PJ3800
Low Voltage Switching Regulator Controller
T
he PJ3800 is a single-channel switching regulator
control IC for low voltage applications incorporating a
SOP-8
TSSOP-8
soft start function and short circuit detection function.
The device has a low minimum operating voltage of 1.8 V and
is ideal for the power supply of battery-operated electronic
equipment.
.
FEATURES
z
Wide supply voltage operating range: 1.8 to 15 V
z
Low current consumption: Typically 5.5 mA in
operation, 1 mA or less in stand-by
z
High speed operation is possible: Maximum 1 MHz
z
The error amplifier gain is set inside the IC, so
ORDER INFORMATION
peripheral components are minimized.
z
Incorporates a soft start circuit.
z
Incorporates a timer-latch type short circuit detection
z
Pin 1. Error amplifier inverting input
2. Soft Star & SCP
3. Power supply
4. Output current setting and control
5. Output
6. Ground
7. Oscillation frequency
8. Error amplifier output
Device
circuit (SCP).
PJ3800CS
Totem-pole type output with adjustable on/off current
PJ3800CA
Operation Temperature
-20 ~ +85℃
Package
SOP-8
TSSOP-8
(for NPN transistors)
z
Incorporates a stand-by function.
BLOCK DIAGRAM
1-8
2003/04.rev.A
PJ3800
Low Voltage Switching Regulator Controller
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Rated Value
Min.
Max.
Unit
Power supply voltage
VCC
—
16
V
Output source current
IO+
—
-50
mA
Output sink current
IO-
—
50
mA
Allowable dissipation
PD
—
570*
mW
Operating temperature
Top
-30
+85
℃
Storage temperature
Tstg
-55
+125
℃
* : When mounted on a 10 cm square double-sided epoxy board
WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current, temperature, etc.)
in excess of absolute maximum ratings. Do not exceed these ratings.
RECOMMENDED OPERATING CONDITIONS
Parameter
Symbol
Values
Unit
Min.
Typ.
Max.
VCC
1.8
—
15
V
VI
–0.2
—
1
V
BR/CTL pin input voltage
VBR
–0.2
—
VCC
V
Output source current
IO+
–40
—
—
mA
Output sink current
IO–
—
—
40
mA
SCP pin capacitance
CPE
—
0.1
—
μF
Phase compensation capacitance
CP
—
0.1
—
μF
Output current setting resistance
RB
150
390
5000
Ω
Timing resistance
RT
1
3
10
kΩ
Timing capacitance
CT
100
270
10000
pF
Oscillation frequency
fOSC
10
500
1000
kHz
Operating temperature
TOP
–30
+25
+85
℃
Power supply voltage
Error amplifier input voltage
WARNING: Recommended operating conditions are normal operating ranges for the semiconductor device. All the device’s
electrical characteristics are warranted when operated within these ranges.
Always use semiconductor devices within the recommended operating conditions. Operation outside
these ranges may adversely affect reliability and could result in device failure.
No warranty is made with respect to uses, operating conditions, or combinations not represented on the data sheet.
Users considering application outside the listed conditions are advised to contact their Promax Johnton
representative beforehand.
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PJ3800
Low Voltage Switching Regulator Controller
ELECTRICAL CHARACTERISTICS (VCC = +2 V, Ta = +25 °C)
Parameter
Circuit to prevent
Reset voltage
malfunction at low
input voltage (U.V.L.O.) Threshold voltage
Charging current
Soft start
Voltage at soft start completion
Short circuit
detection (S.C.P.)
Saw tooth wave
oscillator (OSC)
Error amplifier
Idle period
adjustment section
Symbol
V
VTH
Unit
Min.
Typ.
Max.
—
—
0.9
V
1.1
1.3
1.5
V
VSCP = 0 V
-0.5
-1.0
-0.7
μA
VtS
—
0.7
0.8
0.9
V
Charging current
ICPC
VSCP = 0 V
-1.5
-1.0
-0.7
μA
Threshold voltage
VtPC
—
0.7
0.8
0.9
V
Oscillation frequency
fOCS
RT=3.0kΩ, CT = 270 pF
400
500
600
kHz
Frequency input stability
fdV
VCC = 2 V to 15 V
—
2
10
%
fdT
Ta =-20℃ to +85℃
—
5
—
%
VT
VFB = 450 mV
480
500
520
mV
VT input stability
VTdV
VCC = 2 V to 15 V
—
5
20
mV
VT variation with temperature
VTdT
Ta =-20℃ to +85℃
—
1
—
%
Input bias current
IB
VIN = 0 V
-1.0
-0.2
1.0
μA
Voltage gain
AV
—
70
100
145
V/V
Frequency bandwidth
BW
AV = 0 dB
—
6
—
MHz
Maximum output
voltage range
VOM+
0.78
0.87
—
V
—
0.05
0.2
V
Output source current
IOM+
—
-40
-24
μA
Output sink current
IOM-
24
40
—
μA
Maximum duty cycle
tDUTY
65
75
85
%
1.0
1.2
—
V
Frequency variation with
temperature
Input threshold voltage
VOM-
—
VFB = 0.45 V
RT=3.0kΩ,CT =270pF
VFB =0.8V
RB = 390ΩIO =-15mA
VOH2
RB=750Ω,VCC=1.8V
IO = -10mA
0.8
1
—
V
VOL1
RB = 390Ω,IO=15mA
—
0.1
0.2
V
VOL2
RB = 750Ω VCC=1.8V
IO = 10mA
—
0.1
0.2
V
Output source current
IO+
RB = 390Ω VO = 0.9V
—
-30
-20
mA
Output sink current
IO-
RB = 390Ω VO = 0.3V
30
60
—
mA
Pull down resistance
RO
—
20
30
40
k
Pin voltage
VBR
RB = 390Ω
0.2
0.3
0.4
V
Input off condition
IOFF
-20
—
0
μA
Input on condition
ION
—
—
-45
μA
Pin current range
IBR
-1.8
—
-0.1
mA
Stand-by current
Average supply current
t
ICCS
BR/CTL pin open or VCC
—
—
1
μA
ICC
RB = 390Ω
—
5.5
9.3
mA
Output voltage
Output section
Entire device
—
Value
ICS
VOH1
Output current
setting section/
Control section
Condition
3-8
—
2003/04.rev.A
PJ3800
Low Voltage Switching Regulator Controller
DIAGRAM
HOW TO SET THE TIME CONSTANT FOR SOFT START AND SHORT CIRCUIT DETECTION
1. Soft Start
At power on, the capacitor
CPE
connected to the SCP pin starts charging. The PWM comparator compares the soft start setting
voltage as a proportion of the voltage at the SCP pin with the saw tooth waveform. The comparison controls the ON duty of the
OUT pin, causing the soft start operation. On completion of soft start operation, the voltage at the SCP pin stays low, the soft
start setting voltage stays high, and the circuit enters the output short circuit detection wait state.
Soft start time (The time until the output ON duty reaches approximately 50%)
tS [s] ≅ 0.35 × CPE [μF]
2. Short Circuit Protection
If the switching regulator output suddenly drops due to load effect, the error amplifier output (FB pin) is fixed at VOM + and
capacitor CPE starts charging. When the voltage at the SCP pin reaches approximately 0.8V, the output pin is set low and the
SCP pin stays low.
Once the protection circuit operates, the circuit can be restored by resetting the power supply.
• Short circuit detection time
tPE [s] ≅ 0.8 × CPE [μF]
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PJ3800
Low Voltage Switching Regulator Controller
TYPICAL CHARACTERISTICS
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PJ3800
Low Voltage Switching Regulator Controller
(Continued)
PJ3800
PJ3800
1. Switching Regulator Function
(1) Reference voltage circuit
The reference voltage circuit generates a temperature-compensated reference voltage (@1.25V) from voltage supplied from the
power supply pin. In addition to providing the reference voltage for the switching regulator, the circuit also sets the idle period.
(2) Saw tooth wave oscillator
The saw tooth oscillator generates a saw tooth wave (up to 1 MHz) that is stable with respect to the supply voltage and
temperature. The capacitor and resistor that set the oscillation frequency are connected to the OSC pin (pin 7).
(3) Error amplifier (Error Amp.)
The error amplifier detects the output voltage of the switching regulator and outputs the PWM control signal. The voltage gain is
fixed, and connecting a phase compensation capacitor to the FB pin (pin 8) provides stable phase
compensation for the system.
(4) PWM comparator (PWM Comp.)
The voltage comparator has one inverting and three non-inverting inputs. The comparator is a voltage/pulse width converter that
controls the ON time of the output pulse depending on the input voltage. The output level is high (H) when the saw tooth wave is
lower than the error amplifier output voltage, soft start setting voltage, and idle period setting voltage.
(5) Output circuit
The output circuit has a totem pole type configuration and can drive an external NPN transistor directly. The value of the ON/OFF
current can be set by a resistor connected to the BR/CTL pin .
2. Power Supply Control Function
Stand-by mode (supply current 1 mA or less) can be set by connecting the BR/CTL pin to VCC or by making the pin open circuit.
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PJ3800
Low Voltage Switching Regulator Controller
3. Other Functions
(1) Soft start and short circuit detection
Soft start operation is set by connecting capacitor CPE to the SCP pin (pin 2). Soft start prevents a current spike on start-up.
On completion of soft start operation, the SCP pin (pin 2) stays low and enters the short circuit detection wait state. When an
output short circuit occurs, the error amplifier output is fixed at VOM+ and capacitor CPE starts charging. After charging to
approximately 0.8 V, the output pin (pin 5) is set low and the SCP pin (pin 2) stays low.
Once the protection circuit operates, the circuit can be restored by resetting the power supply. (See “n HOW TO SET THE TIME
CONSTANT FOR SOFT START AND SHORT CIRCUIT DETECTION”.)
(2) Circuit to prevent malfunction at low input voltage
Transients when powering on or instantaneous glitches in the supply voltage can lead to malfunction of the control IC and cause
system damage or failure. The circuit to prevent malfunction at low input voltage detects a low input voltage by comparing the
supply voltage to the internal reference voltage. On detection, the circuit fixes the output pin to low.
The system recovers when the supply voltage rises back above the threshold voltage of the malfunction prevention circuit.
APPLICATION EXAMPLE
PJ3800
USAGE PRECAUTIONS
1. Do not apply an input voltage greater than the maximum rating.
Do not input voltages greater than the maximum rating as this can cause damage to the LSI
2. Use in accordance with the recommended operating conditions.
The electrical characteristics of the LSI are not guaranteed if the input voltage is greater than the maximum. Also, LSI operation is
unstable if the input voltage is less than the minimum. Therefore, always use in accordance with the recommended operating
conditions.
3. Use a wide ground line on the printed circuit board.
As the LSI uses a high frequency and therefore can generate high frequency noise, make the ground line as wide as possible.
4. Take anti-static precautions.
• Use a holder for inserting the semiconductor which is anti-static or conductive.
• After mounting the device on a printed circuit board, store or transport the board in a conductive bag or container.
• Earth work benches, tools, and measuring equipment.
• Ensure that maintenance personnel have a resistance of 250 kW to 1 MW in series between their body and earth.
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