FUJITSU SEMICONDUCTOR
DATA SHEET
DS04-27205-5E
ASSP Power Supplies
BIPOLAR
Switching Regulator Controller
MB3782
s
DESCRIPTION
The FUJITSU MB3782 is a PWM-type switching regulator controller, designed with open-collector output for
connection to external drive transistors and coils, providing a selection of three types of output voltage: step-up,
step-down or inverting (inverting output is available on one circuit only).
The MB3782 features identical oscillator output waveforms to enable completely synchronous operation and
prevent the occurrence of low-frequency beat between channels.
Also, the MB3782 features low power dissipation (2.1 mA Typ) and a built-in standby mode (10
µA),
making
possible the configuration of a wide variety of high-efficiency, stable power supplies, even with the use of battery
power. The MB3782 is an ideal power supply for high-performance portable devices such as video camcorders
and cameras.
s
FEATURES
•
•
•
•
•
•
•
•
Wide voltage range (3.6 V to 18 V)
Low power dissipation (operating mode: 2.1 mA (Typ), standby mode: 10
µA
(Max)
Wide range of oscillator frequencies, high-frequency capability (1 to 500 kHz)
On-chip timer-latch type short detection circuit
On-chip undervoltage lockout circuit
On-chip 2.50 V reference voltage circuit (1.25 V output available at R
T
pin)
Dead time adjustment over full duty cycle range
On-chip standby mode (power on/off function)
s
PACKAGE
Plastic DIP 20 pin
,
Plastic SOP 20 pin
,
(DIP-20P-M01)
(FPT-20P-M01)
MB3782
s
PIN ASSIGNMENT
TOP VIEW
V
REF
C
T
R
T
+ IN1
– IN1
FB1
DTC1
PUT1
GND
OUT2
1
2
3
4
5
6
7
8
9
10
V
CC
CTL
– IN3
FB3
DTC3
OUT3
SCP
– IN2
FB2
DTC2
20
19
18
17
16
15
14
13
12
11
(DIP-20P-M01)
(FPT-20P-M01)
s
PIN DESCRIPTION
Pin No.
1
2
Pin Name
V
REF
C
T
I/O
O
—
Description
2.50 V (typ) voltage output: provides load current up to 3 mA,
for use as error amplifier reference input and for dead time
setting.
Oscillator timing capacity connection: should be used in the
capacity range 150 to 15000 pF.
Oscillator timing resistor connection: should be used in the
resistance range 5.1 to 100 kΩ. This pin can also provide
output at voltage level V
REF
/2, for use as error amplifier
reference input.
Error amplifier 1 non-inverting input pin.
Error amplifier 1 inverting input pin.
Error amplifier 1 output pin: connect resistor and capacitor
between this pin and the –IN1 pin to set gain and adjust
frequency characteristics.
OUT1 dead time setting pin: V
REF
voltage is divided by an
external resistor and applied to set dead time. Also, a capacitor
may be connected between this pin and the GND pin to perform
soft start operations.
3
4
5
6
R
T
+IN1
–IN1
FB1
—
I
I
O
7
DTC1*
1
I
(Continued)
2
MB3782
(Continued)
Pin No.
8
9
10
Pin Name
VOUT1
GND
OUT2
I/O
O
—
O
Description
Open collector type output pin with an emitter connected to
GND.
Output current may be up to 50 mA.
Ground pin
Open collector type output pin with an emitter connected to
GND. Output current may be up to 50 mA.
Used to set OUT2 pin dead time. V
REF
voltage is divided by an
external resistor and applied to set dead time. Also, a capacitor
may be connected between this pin and the GND pin to perform
soft start operations.
Error amplifier 2 output pin: connect resistor and capacitor
between this pin and the –IN2 pin to set gain and adjust
frequency characteristics.
Error amplifier 2 inverting input pin.
Time constant setting capacitor connection for timer-latch
type short prevention circuit: a capacitor should be connected
between this pin and the GND pin. For details, see “s Setting
the Time Constant for the Timer-Latch Type Short Prevention
Circuit.”
Open collector type output pin for emitter connected to GND.
Output current may be up to 50 mA.
Used to set OUT3 pin dead time. V
REF
voltage is divided by an
external resistor and applied to set dead time. Also, a capacitor
may be connected between this pin and the GND pin to perform
soft start operations.
Error amplifier 3 output pin: connect resistor and capacitor
between this pin and the –IN3 pin to set gain and adjust
frequency characteristics.
Error amplifier 3 inverting input pin.
Power supply control pin: low level places the IC in standby
mode and reduces power consumption to 10
µA
or lower. Input
level may be driven by TTL or CMOS.
Power supply pin: voltage range is 3.6 to 18 V.
11
DTC2*
1
I
12
13
FB2
–IN2
O
I
14
SCP*
2
—
15
OUT3
O
16
DTC3*
1
I
17
18
19
20
FB3
–IN3
CTL
V
CC
O
I
I
—
*1: DTC = Dead Time Control
*2: SCP = Short Circuit Protection
3
MB3782
s
BLOCK DIAGRAM
R
T
3
C
T
2
V
REF
1
V
CC
20
CLT
19
1.25 V
2.5 V
Triangular wave
oscillator
Reference
voltage
source
Power on/off
control
circuit
9
GND
Error Amp.1
+ IN1
– IN1
FB1
DTC1
4
PWM Comp.
Ch.1
+
+
–
8
+
–
OUT1
5
6
7
Error Amp.2
– IN2
13
PWM Comp.
+
+
–
–
+
1.25 V
Ch.2
10
OUT2
FB2
DTC2
12
11
Error Amp.3
– IN3
18
PWM Comp.
+
+
–
–
+
1.25 V
Ch.3
15
OUT3
FB3
DTC3
17
16
SCP Comp.
–
–
–
+
2.1 V
V
REF
1
µA
SCP
14
S
Latch
R
U.V.L.O.
4
MB3782
s
FUNCTIONAL DESCRIPTIONS
1. Reference Voltage Source
The reference voltage source uses the voltage provided at the power supply pin (pin 20) to generate a temper-
ature-compensated reference voltage (≅ 2.50 V), which is used as the operating power supply for the internal
circuits of the IC. The reference voltage source can be output through the V
REF
pin (pin 1).
2. Triangular Wave Oscillator
By connecting a timing capacitor and resistor respectively to the C
T
pin (pin 2) and R
T
pin (pin 3), the oscillator
can provide a triangular waveform at any desired frequency.
The waveform has an amplitude of 1.3 V to 1.9 V, and can be connected to the non-inverting input of the on-
chip PWM comparator and also output through the C
T
pin.
3. Error Amps
The error amps are amplifiers that detect the output voltage of the switching regulator and send the PWM control
signal. The common-mode input voltage range is 1.05 V to 1.45 V, so that the voltage applied to the non-inverting
input pin as a reference voltage should be either the voltage obtained by dividing the IC reference voltage output
(recommended value: V
REF
/2) or the voltage obtained from the R
T
pin (1.25 V). The non-inverting input for the
error amps 1 and 2 is internally connected to V
REF
/2 voltage.
Also, a feedback transistor and capacitor can be connected between the error amp output pin and inverting input
pin to provide any desired level of loop gain, enabling stable phase compensation.
4. Timer Latch (S-R Latch) Type Short Prevention Circuit
The timer-latch type short prevention circuit detects the output levels from each of the error amps. Whenever
one or more error amps produces an output level of 2.1 V or higher, the timer circuit is activated starting the
charging of the external protection enabler capacitor.
If the error amp output voltage does not return to normal range before the voltage in this capacitor reaches the
transistor’s base-emitter junction voltage (V
BE
(≅ 0.65 V)), the latch circuit will operate to turn the output transistor
off and at the same time set the dead time to 100%.
Once the prevention circuit is activated, the power must be switched on again to resume normal operation.
5. Low Input Voltage Fault Prevention Circuit (Under Voltage Lock-Out (UVLO) function)
When power is switched on, excess power or momentary drops in power line current can cause operating faults
in the controller IC, which can in turn lead to damage or deterioration in systems.
The low input voltage fault prevention circuit detects the internal reference voltage level with respect to the power
supply voltage level and acts to reset the latch circuit, thereby turning the output transistor off and at the same
time setting the dead time to 100% and holding the SCP pin (pin 14) at “low.” Operation returns to normal when
the power supply voltage reaches or exceeds the UVLO threshold voltage level.
6. PWM Comparator
The PWM comparator is a voltage comparator with one inverting and two non-inverting inputs, which acts as a
voltage to pulse width converter controlling the on-time of the output pulse according to the input voltage level.
When the triangular waveform produced by the oscillator is lower than either the error amp output or the DTC
pin voltage, the output transistor is switched on.
It is also possible to use the DTC terminal to provide a soft start function.
7. Output Transistor
The output is open-collector type, with the emitter of the output transistor connected to the GND pin. The power
transistor for external switching can carry a base current of up to 50 mA.
8. Power Supply Control
Power supply on/off control is enabled through the CTL pin (pin 19). (In standby mode, power supply current is
10
µA
or less.)
5
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