Fujitsu MB3788 User manual

DS04-27209-3E
FUJITSU SEMICONDUCTOR
DATA SHEET
ASSP
SWITCHING REGULATOR
CONTROLLER
MB3788
■
■■
■DESCRIPTION
The MB3788 is a dual-channel PWM-type switching regulator controller; it incorporates a reference voltage.
The MB3788 has a PWM circuit and an output circuit as well as a reference voltage power supply with a voltage
accuracy of ±1%. The maximum operating frequency is 1 MHz. It is designed for a voltage-drop output switching
regulator suitable for a logic power supply or speed control of a DC motor.
The MB3788 is compatible with all master ICs producing triangular waves, saw-tooth waves and sine waves with
an amplitude of 1.3 V to 1.9 V.
Itcanbeusedinhigh-performanceportableequipmentsuchasavideocamcorderornotebookpersonalcomputer
(word processor).
■
■■
■FEATURES
• Wide operating power supply voltage range: 3.6 V to 18 V
• Low power dissipation
• Operating: 1.9 mA (standard)
Standby: 10 µA Max
(Continued)
■
■■
■PACKAGE
This device contains circuitry to protect the inputs against damage due to high static voltages or electric fields. However, it is
advised that normal precautions be taken to avoid application of any voltage higher than maximum rated voltages to this high
impedance circuit.
24-pin Plastic SSOP
(FPT-24P-M03)

MB3788
2
(Continued)
• High-frequency operation: 100 kHz to 1 MHz
• On-chip timer and latch-type short-circuit detection circuit
• Wide error amplifier input voltage range: -0.2 V to VCC - 1.8 V
• On-chip high-accuracy reference voltage circuit: 2.50 V ±1%
• Output circuit
PNP transistor drive output pin: Push-pull type
ON/OFF current values set independently
• On-chip standby function and output control function
• High-density packaging: SSOP-24P
■
■■
■PIN ASSIGNMENT
(TOP VIEW)
VCC(out)
OUT1
VE1
Cb1
Ca1
FB1
-IN1(E)
+IN1(E)
-IN1(C)
-IN(PWN)
VCC
VREF
GND
OUT2
VE2
Cb2
Ca2
FB2
-IN2(E)
+IN2(E)
-IN2(C)
SCP
CTL2
CTL1
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
(FPT-24P-M03)

MB3788
3
■
■■
■PIN DESCRIPTION
Note: The alphabetic characters in parenthesis above indicate the following input pins.
(C): Comparator
(E): Error amplifier
Pin No. Pin name I/O Descriptions
Channel 1
2OUT1O
Channel 1 push-pull type output
3VE1I
Channel 1 output current setting
4Ca1—
Channel 1 output transistor OFF current setting: Output transistor OFF
The current is set by connecting a capacitor between pins Ca1 and Cb1.
5Cb1—
6FB1O
Channel 1 error amplifier output
7-IN1(E)I
Channel 1 error amplifier inversion input
8+IN1(E) Channel 1 error amplifier non-inversion input
9-IN1(C)I
Channel 1 comparator inversion input
Channel 2
16 -IN2(C) I Channel 2 comparator inversion input
17 +IN2(E) I Channel 2 error amplifier non-inversion input
18 -IN2(E) I Channel 2 error amplifier inversion input
19 FB2 O Channel 2 error amplifier output
20 Ca2 — Channel 2 output transistor OFF current setting: Output transistor OFF
The current is set by connecting a capacitor between pins Ca2 and Cb2.
21 Cb2 —
22 VE2 I Channel 2 output current setting
23 OUT2 O Channel 2 push-pull type output
Control
circuit
13 CTL1 I Power and channel 1 control pin
H level: Power and channel 1 operating
L level: Standby
14 CTL2 I Channel 2 control pin
When CTL1 pin = H level,
H level: Channel 2 operating
L level: Channel 2 OFF
15 SCP — Short-circuit protection circuit capacitor connection
Power
circuit
1VCC2—Output circuit power pin
10 -IN(PWM) I Master oscillating waveform input
11 VCC1 —Reference power and control circuit power
12 VREF OReference voltage output
24 GND — Ground

MB3788
4
■
■■
■BLOCK DIAGRAM
24
Channel 1
-IN1 (E)
FB1
-IN1 (C)
+IN1 (E) 1
2
5
4
Ca1
VCC(out)
OUT1
Cb1
11
13
14
3
CTL2
VCC
CTL1
VE1
10 12 GND
-IN(PWM)
SCP
VREF
1.9 V
1.3 V
+
-
+
-
+
-
1.5 V
0.6 V
Error amplifier 1
Comparator 1
PWM comparator 1 OFF current setting
23
21
20
22
Channel 2
-IN2 (E)
FB2
-IN2 (C)
+IN2 (E)
Cb2
OUT2
Ca2
VE2
+
-
+
-1.5 V
0.6 V
Error amplifier 2
Comparator 2
PWM comparator 2 OFF current setting
-
-
+
SCP comparator
2.1 V
Low input
voltage
protection
circuit
SR latch
circuit
Reference
voltage
power (2.5 V)
Power/channel
ON/OFF
circuit
Timer circuit
1 µA
VREF
+
-
15
9
7
6
8
16
18
19
17

MB3788
5
■
■■
■FUNCTIONAL DESCRIPTION
1. Major Functions
(1) Reference voltage power circuit
Thereference voltagepowersupply produces a referencevoltage(≈2.50V)whichistemperature-compensated
by the voltage supplied from the power pin (pin 11); it is used as the IC internal circuit operating power supply.
The reference voltage can also be output externally at 1 mA from VREF pin (pin12).
(2) Error amplifier
The error amplifier detects the switching regulator output voltage and outputs a PWM control signal. It has a
wide in-phase input voltage range of -0.2 V to VCC - 1.8 V to make setting from an external power supply easy.
Connecting the output pin and inversion input pin of the error amplifier through a feedback resistor and capacitor
allows setting of any loop gain to provide stable phase compensation.
(3) PWM comparator
The PWM comparator controls the output pulse ON time according to the input voltage.
The voltage input to the -IN pin (PWM) turns the output transistor on when it is lower than the output voltage of
the error amplifier.
(4) Output circuit
The output circuit is configured in a push-pull form and uses a PNP transistor drive system to drive a transistor
of up to 30 mA. (See
How to Set Output Current. )
2. Channel Control Function
Channels can be set ON/OFF by combining the voltage levels at pin CTL1 (pin 13) and pin CTL2 (pin 14).
Channel ON/OFF Setting Conditions
*: The power current in the standby state is 10 µA Max.
Voltage level at CTL pin Channel ON/OFF status
CTL1 CTL2 Power circuit Channel 1 Channel
L×Stand by state*
HH ON ON
LOFF

MB3788
6
3. Protection Functions
(1) Timer and latch-type short-circuit protection circuit
The SCP comparator detects the output voltage levels of two comparators to detect an output short circuit. If
the output voltage of one comparator increases to 2.1 V, the transistor of the timer circuit is turned off and the
short circuit protection capacitor connected externally to the SCP pin (pin 15) starts charging.
The latch circuit turns off the output transistor and simultaneously clears the duty cycle to 0 when the output
voltage level of the comparator does not return to the normal voltage level until the capacitor voltage rises to the
base-emitterjunctionvoltage VBE (≈0.65 V) of the transistor. (See
Howto Set Time Constant forTimer & Latch-
Type Short-Circuit Protection Circuit.
)
When the protection circuit operates, recycle the power to reset the circuit.
(2) Low input voltage malfunction fail-safe circuit
A transient at power-on, or an instantaneous supply voltage drop can cause a control IC malfunction, which may
damage the system. The low input voltage malfunction fail-safe circuit detects the internal reference voltage
level based on the supply voltage level, resets the latch circuit, turns off the output transistor, clears the duty
cycle to 0 and holds the SCP pin (pin 15) at Low level. All circuits are recovered when the supply voltage is
greater than the threshold voltage of the fail-safe circuit.

MB3788
7
■ABSOLUTE MAXIMUM RATINGS
*:Value obtained when mounted on 4 cm ×4 cm double-sided epoxy substrate
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
WARNING: The recommended operating conditions are required in order to ensure the normal operation of the
semiconductor device. All of the device’s electrical characteristics are warranted when the device is
operated within these ranges.
Always use semiconductor devices within their recommended operating condition ranges. 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
FUJITSU representatives beforehand.
(TA = +25°C)
Parameter Symbol Conditions Ratings Unit
Min Max
Supply voltage VCC ——
20 V
Control input voltage VICTL ——
20 V
Allowable loss PDTa ≤+25°C—500* mW
Operating ambient temperature TOP —-30 +85 °C
Storage temperature Tstg —-55 +125 °C
(TA= +25°C)
Parameter Symbol Conditions Values Unit
Min Typ Max
Supply voltage VCC —3.66.018V
Reference voltage output current IOR —-1—0mA
Error amplifier input voltage VI—-0.2—V
CC - 1.8 V
Error amplifier input voltage VI—-0.2—V
CC V
Control input voltage VICTL —-0.2—18V
Output current IO—3.0—30mA
Operating frequency fosc — 100 300 1000 kHz
Operating ambient temperature Top — -30 25 85 °C

MB3788
8
■
■■
■ELECTICAL CHARACTERISTICS
(Continued)
(VCC =6V, TA= +25°C)
Parameter Symbol Conditions Value Unit
Min Typ Max
Reference
voltage
Reference voltage VREF IOR = -1 mA 2.475 2.500 2.525 V
Output voltage temperature
variation ∆VREF/
VREF TA= -30°to +85°C-2±0.2 2 %
Input stability Line VCC = 3.6 V to 18 V — 2 10 mV
Load stability Load IOR = -0.1 mA to 1 mA — 3 10 mV
Short-circuit output current IOS VREF = 2 V -20 -8 -3 mA
Low voltage
malfunction
fail-safe
circuit
Threshold voltage VtH ——2.65—V
VtL ——2.45—V
Hysteresis width VHYS —80200—mV
Reset voltage VR—1.51.9—V
Short-circuit
detection
comparator
Input offset voltage VIO — 0.58 0.65 0.72 V
Input bias current IIB VI= 0 V -200 -100 — nA
In-phase input voltage range VICM —-0.2—V
CC-1.8 V
Short-circuit
detector
Threshold voltage VtPC — 0.60 0.65 0.70 V
Input standby voltage VSTB — — 50 100 mV
Input latch voltage VI— — 50 100 mV
Input source current IIbpc — -1.4 -1.0 -0.6 µA
Error
amplifier
Input offset voltage VIO VFB = 1.6 V -10 — 10 mV
Input offset current IIO VFB = 1.6 V -100 — 100 nA
Input bias current IIB VFB = 1.6 V -200 -60 — nA
In-phase input voltage range VICM —-0.2—V
CC-1.8 V
Voltage gain AV—60100—dB
Frequency bandwidth BW AV= 0 dB — 800 — kHz
In-phase signal rejection ratio CMRR — 60 80 — dB
Maximum output voltage width VOM+ —V
REF-0.3 2.4 — V
VOM- — — 0.05 0.5 V
Output sink current IOM+ VFB = 1.6 V — 120 — µA
Output source current IOM- VFB = 1.6 V — -2 — mA

MB3788
9
(Continued)
Parameter Symbol Conditions Values Unit
Min Typ Max
PWM
comparator
Threshold voltage Vt0 Duty cycle = 0 % 1.05 1.3 — V
Vt100 Duty cycle = 100 % — 1.9 2.25 V
Input sink current IIM+ ——120—µA
Input source current IIM- ——-2—mA
Input bias current IIB VI = 0 V -1.0 -0.5 — µA
Control
Threshold voltage Vth — 0.7 1.4 2.1 V
Input current IIH VCTL = 5 V — 100 200 µA
IIL VCTL = 0 V -10 — 10 µA
Output
Source current IO——-40—mA
Sink current IORB= 50 Ω18 30 42 mA
Output leak current ILO VO= 18 V — — 20 µA
All devices Standby current ICCO ——010µA
Power current at output OFF ICC ——1.92.7mA

MB3788
10
■STANDARD CHARACTERISTIC CURVES
(Continued)
2.5
2.0
1.5
1.0
0.5
0048121620
Power
current
lCC (mA)
Supply voltage VCC (V)
5
4
3
2
1
00 4 8 12 16 20
Reference
voltage
VREF (V)
Supply voltage VCC (V)
CTL1, 2 = 6 V
5
4
3
2
1
0
012345
Reference
voltage
VREF (V)
Supply voltage VCC (V)
VE
VREF
2.56
2.54
2.52
2.50
2.48
2.46
2.44
-60 -40 -20 0 20 40 60 80 100
Reference
voltage
VREF (V)
Ambient temperature TA (°C)
5
4
3
2
1
0
Output
current
setting
pin voltage
VE(V)
VCC = 6 V
VCTL1, 2 = 6 V
IOR = -1 mA
1. Power current - supply voltage characteristic 2. Reference voltage - supply voltage characteristic
3.Reference voltage, output current setting pin voltage
- supply voltage characteristic 4. Reference voltage - ambient temperature characteristic
3.0
2.8
2.6
2.4
2.2
2.0
012345
Reference
voltage
VREF (V)
Control voltage VCTL1 (V)
500
400
300
200
100
0048121620
Control
current
lCTL1 (µA)
Control voltage VCTL1 (V)
5. Reference voltage - control voltage characteristic 6. Control current - control voltage characteristic
TA= +25°C
TA= +25°C
VCC = 6 V
TA= +25°CVCC = 6 V TA= +25°C
CTL1 = 6 V
TA= +25°C