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FUJITSU SEMICONDUCTOR DATA SHEET
DS04-27211-3E
ASSP For Power Supply Applications
BIPOLAR
Switching Regulator Controller
(Supporting External Synchronization)
MB3789
s DESCRIPTION
The MB3789 is a PWM (pulse width modulation) switching regulator controller supporting an external sync signal. The MB3789 incorporates two error amplifiers which can be used respectively for voltage control and current control, allowing the IC to serve as a DC/DC converter with current regulating functions. The MB3789 is the ideal IC for supplying power to the back-lighting fluorescent tube for a liquid crystal display (LCD) device such as a camera-integrated VTR.
DataShee
s FEATURES
• • • • • • • • •
DataSheet4U.com Wide range of operating power supply voltages: 3 V to 18 V Low current consumption: 1.5 mA (Typ.) Wide input voltage range of error amplifier: –0.2 V to VCC – 1.8 V Built-in two error amplifier Oscillator capable of operating with an external sync signal Built-in timer latch short protection circuit Variable dead time provides control over total operating range Output supporting a power MOSFET 16-pin SSOP package mountable at high density
s PACKAGE
16-pin Plastic SSOP
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(FPT-16P-M05)
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MB3789
s PIN ASSIGNMENT
(TOP VIEW)
VCC1
1
16
GND
VREF
2
15
OUT
CT
3
14
VCC2
SYNC
4
13
CB
SCP
*1
5
12
DTC FB2 *2
FB1
6
11
et4U.com
−IN1 *1 +IN1 *1
7
10
−IN2 *2 +IN2 *2
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8
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9
(FPT-16P-M05) *1: Pins on error amplifier 1 *2: Pins on error amplifier 2
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2
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MB3789
s PIN DESCRIPTION
Pin no. 7 8 6 10 I/O control unit 9 11 13 5 12 15 Sawtooth waveform oscillator 3 Pin symbol –IN1 +IN1 FB1 –IN2 +IN2 FB2 CB SCP DTC OUT CT I/O I I O I I O — — I O — Function Error amplifier 1 inverting input pin Error amplifier 1 noninverting input pin Error amplifier 1 output pin Error amplifier 2 inverting input pin Error amplifier 2 noninverting input pin Error amplifier 2 output pin Output bootstrap pin. Connect a capacitor between the CB and OUT pins to bootstrap the output transistor. Capacitor connection pin for short-circuit protection circuit Dead time control pin Totem-pole output pin Sawtooth waveform frequency setting capacitor/resistor connection pin
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4 1 14 2 16 SYNC VCC1 VCC2 VREF GND I — — O —
DataSheet4U.com External sync signal input pin
Reference power supply, control circuit power-supply pin Output circuit power-supply pin Reference voltage output pin Ground pin
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3
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Power-supply circuit
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MB3789
s BLOCK DIAGRAM
Error amp. 1 +IN1 8 −IN1 7 FB1 6 Error amp. 2 +IN2 9 −IN2 10 FB2 11 DTC 12
PWM comparator
13
CB
14 VCC2
OUT 15
10 kΩ
−0.9 V 8 µA SCP comparator 1 4 µA −0.3 V
1.25 V 1.25 V 2 µA SCP comparator 2 VCC1 1 1.1 V VREF 2 Reference Power voltage ON/OFF supply circuit SCP comparator 3 VREF
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1.8 V
SR latch
Under voltage Lock-out protection circuit
Sawtooth wave oscillator
16 GND
5 SCP External sync signal SYNC
4
3 CT
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4
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MB3789
s FUNCTIONAL DESCRIPTION
1. Switching Regulator Functions
(1) Reference voltage generator The reference voltage generator uses the voltage supplied from the power supply pin (pin 1) to generate a temperature-compensated, reference voltage (about 2.50 V) as the reference supply voltage for the IC’s internal circuitry. The reference voltage can be output, up to 50 µA, to an external device through the VREF pin (pin 2). This regulated reference voltage can be used as the reference voltage for the switching regulator and also used for setting the dead time. (2) Sawtooth waveform oscillator With a timing capacitor and a timing resistor connected to the CT pin (pin 3), the sawtooth waveform oscillator generates a sawtooth wave which remains stable even with supply voltage variations or temperature changes. The sawtooth wave is input to the PWM comparator. The amplitude of oscillating waveform is 0.3 V to 0.9 V. In addition, the oscillator can be used for external synchronization, where it generates a sawtooth waveform synchronous to the input signal from the SYNC pin (pin 4). (3) Error amplifiers The error amplifiers detect the output voltage from the switching regulator and outputs the PWM control signal. Since they support a wide range of in-phase input voltages from –0.2 V to “VCC – 1.8 V”, they can be set easily from an external power supply. An arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the error amplifier output DataSheet4U.com pin to the inverting input pin, enabling stable phase compensation to the system. The MB3789 can make a current-regulated DC/DC converter using the two internal error amplifiers respectively for voltage control and current control. (4) PWM comparator The PWM comparator is a voltage comp.