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FUJITSU SEMICONDUCTOR DATA SHEET
DS04-27209-1E
ASSP
SWITCHING REGULATOR CONTROLLER
MB3788
s
DESCRIPTION
24-PIN PLASTIC SSOP
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, sawtooth waves and sine waves with an amplitude of 1.3 to 1.9 V. It can be used in high-performance portable equipment such as a video camcorder or notebook personal computer (word processor).
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FEATURES
- Wide operating power supply voltage range: 3.6 to 18 V - Low power dissipation - Operating: 1.9 mA (standard) Standby: 10 A max. - 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
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.
(FPT-24P-M03)
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PIN ASSIGNMENT
(TOP VIEW) VCC(out) OUT1 VE1 Cb1 Ca1 FB1 -IN1(E) +IN1(E) -IN1(C) -IN(PWN) VCC VREF 1 2 3 4 5 6 7 8 9 10 11 12 (FPT-24P-M03) 24 23 22 21 20 19 18 17 16 15 14 13 GND OUT2 VE2 Cb2 Ca2 FB2 -IN2(E) +IN2(E) -IN2(C) SCP CTL2 CTL1
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PIN DESCRIPTION
Pin No. 2 3 4 Channel 1 5 6 7 8 9 16 17 18 Channel 2 19 20 21 22 23 13 Control circuit Pin name OUT1 VE1 Ca1 Cb1 FB1 -IN1(E) +IN1(E) -IN1(C) -IN2(C) +IN2(E) -IN2(E) FB2 Ca2 Cb2 VE2 OUT2 CTL1 I I I I O -- -- I O I I/O O I -- -- O I Descriptions
Channel 1 push-pull type output Channel 1 output current setting Channel 1 output transistor OFF current setting: Output transistor OFF The current is set by connecting a capacitor between pins Ca1 and Cb1. Channel 1 error amplifier output Channel 1 error amplifier inversion input Channel 1 error amplifier non-inversion input Channel 1 comparator inversion input Channel 2 comparator inversion input Channel 2 error amplifier non-inversion input Channel 2 error amplifier inversion input Channel 2 error amplifier output Channel 2 output transistor OFF current setting: Output transistor OFF The current is set by connecting a capacitor between pins Ca2 and Cb2. Channel 2 output current setting Channel 2 push-pull type output Power and channel 1 control pin H level: Power and channel 1 operating L level: Standby Channel 2 control pin When CTL1 pin = H level, H level: Channel 2 operating L level: Channel 2 OFF Short-circuit protection circuit capacitor connection Output circuit power pin Master oscillating waveform input Reference power and control circuit power Reference voltage output Ground
14 15 1 10
CTL2 SCP VCC2 -IN(PWM) VCC1 VREF GND
I -- -- I -- O --
Power circuit
11 12 24
Note:
The alphabetic characters in parenthesis above indicate the following input pins. (C): Comparator (E): Error amplifier
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BLOCK DIAGRAM
Cb1 Channel 1
4 5
Ca1 +IN1 (E) -IN1 (E) FB1
8
+ -
Error amplifier 1 + PWM comparator 1
OFF current setting
1
VCC(out)
7
2
OUT1
6
+ -IN1 (C)
9
Comparator 1 1.5 V
3
0.6 V -
VE1
Ca2 Channel 2
20 21
Cb2 +IN2 (E) -IN2 (E) FB2
17
+ -
Error amplifier 2 + PWM comparator 2
OFF current setting
18
23
OUT2
19
+ 0.6 V -IN2 (C)
16
Comparator 2 1.5 V
22
-
VE2
Timer circuit 1 A SCP
SCP comparator + 2.1 V
14
CTL2
1.9 V 1.3 V
15
VREF SR latch circuit Low input voltage protection circuit
10
11
VCC
Reference Power/channel ON/OFF voltage circuit power (2.5 V)
13
CTL1
12
24
-IN(PWM)
VREF
GND
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FUNCTIONAL DESCRIPTION
1. Major Functions
(1) Reference voltage power circuit
The reference voltage power supply produces a reference voltage ( 2.50 V) which is temperature-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
Voltage level at CTL pin CTL1 L H CTL2 x H
Channel ON/OFF status Power circuit Channel 1 Stand by state* ON ON OFF Channel
L
*The power current in the standby state is 10 A max.
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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-emitter junction voltage VBE ( 0.65 V) of the transistor. (See How to Set Time Constant for Timer & 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.
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ABSOLUTE MAXIMUM RATINGS
(TA = +25C) Parameter Symbol VCC VICTL PD TOP Tstg Conditions
-- --
Ratings 20 20 500* -30 to +85 -55 to +125
Unit V V mW C C
Supply voltage Control input voltage Allowable loss Operating ambient temperature Storage temprature
Ta +25C
-- --
* Value obtained when mounted on 4 cm x 4 cm double-sided epoxy substrate
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RECOMMENDED OPERATING CONDITIONS
(TA = +25C) Parameter Symbol VCC IOR VI VI VICTL IO fosc Top Conditions -- -- -- -- -- -- -- -- Values Min. 3.6 -1 -0.2 -0.2 -0.2 3.0 100 -30 Typical 6.0 -- -- -- -- -- 300 25 Max. 18 0 VCC - 1.8 VCC 18 30 1000 85 Unit V mA V V V mA kHz C
Supply voltage Reference voltage output curren Error amplifier input voltage Error amplifier input voltage Control input voltage Output current Operating frequency Operating ambient temperature
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ELECTICAL CHARACTERISTICS
(VCC =6V, TA = +25C) Value Parameter Reference voltage Output voltage temperature variation Input stability Load stability Short-circuit output current Symbol VREF VREF/ VREF Line Load IOS VtH Conditions Min. IOR = -1 mA TA = -30 to +85C VCC = 3.6 V to 18 V IOR = -0.1 mA to 1 mA VREF = 2 V -- -- -- -- -- VI = 0 V -- -- -- -- -- VFB = 1.6 V VFB = 1.6 V VFB = 1.6 V -- -- AV = 0 dB -- -- -- VFB = 1.6 V VFB = 1.6 V 2.475 -2 -- -- -20 -- -- 80 1.5 0.58 -200 -0.2 0.60 -- -- -1.4 -10 -100 -200 -0.2 60 -- 60 VREF-0.3 -- -- -- Typical 2.500 0.2 2 3 -8 2.65 2.45 200 1.9 0.65 -100 -- 0.65 50 50 -1.0 -- -- -60 -- 100 800 80 2.4 0.05 120 -2 Max. 2.525 2 10 10 -3 -- -- -- -- 0.72 -- VCC-1.8 0.70 100 100 -0.6 10 100 -- VCC-1.8 -- -- -- -- 0.5 -- -- V % mV mV mA V V mV V V nA V V mV mV A mV nA nA V dB kHz dB V V A mA Unit
Reference voltage
Low voltage malfunction fail-safe circuit
Threshold voltage VtL Hysteresis width Reset voltage VHYS VR VIO IIB VICM VtPC VSTB VI IIbpc VIO IIO IIB VICM AV BW CMRR VOM+ Maximum output voltage width VOMOutput sink current Output source current IOM+ IOM-
Short-circuit detection comparator
Input offset voltage Input bias current In-phase input voltage range Threshold voltage
Short-circuit detector
Input standby voltage Input latch voltage Input source current Input offset voltage Input offset current Input bias current In-phase input voltage range Voltage gain
Error amplifier
Frequency bandwidth In-phase signal rejection ratio
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Values Parameter
Threshold voltage Vt100 PWM comparator Input sink current Input source current Input bias current Threshold voltage Control Input current IIL Source current Output Sink curren Output leak current Standby current All devices Power current at output OFF IO IO ILO ICCO ICC VCTL = 0 V -- RB = 50 VO = 18 V -- -- -10 -- 18 -- -- -- -- -40 30 -- 0 1.9 10 -- 42 20 10 2.7 IIM+ IIMIIB Vth IIH VI = 0 V -- VCTL = 5 V Duty cycle = 100 % -- -- -- -- -- -1.0 0.7 -- 1.9 120 -2 -0.5 1.4 100 2.25 -- -- -- 2.1 200
Symbol
Vt0
Conditions
Duty cycle = 0 %
Min.
1.05
Typical
1.3
Max.
--
Unit
V V A mA A V A A mA mA A A mA
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STANDARD CHARACTERISTIC CURVES
1. Power current - supply voltage characteristic 2.5 2.0 CTL1, 2 = 6 V Power 1.5 current lCC (mA) 1.0 0.5 0 0 4 8 12 16 20 Supply voltage VCC (V) 3.Reference voltage, output current setting pin voltage - supply voltage characteristic TA = +25C 5 4 3 Output 2 current setting pin voltage 1 VE (V) 0 1 2 3 4 5 Supply voltage VCC (V) 5. Reference voltage - control voltage characteristic VCC = 6 V TA = +25C 6. Control current - control voltage characteristic VCC = 6 V TA = +25C Reference 3 voltage VREF (V) 2 1 0 0 TA = +25C CTL1 = 6 V 2. Reference voltage - supply voltage characteristic 5 4 TA = +25C
4
8
12
16
20
Supply voltage VCC (V) 4. Reference voltage - ambient temperature characteristic 2.56 Reference 2.54 voltage VREF (V) 2.52 2.50 2.48 2.46 2.44 -60 -40 -20 0 20 40 60 80 100 Ambient temperature TA (C) VCC = 6 V VCTL1, 2 = 6 V IOR = -1 mA
5 4 Reference voltage 3 VREF (V) 2 1 0 0
VREF
VE
3.0 2.8 Reference voltage 2.6 VREF (V) 2.4 2.2 2.0 0
500 400 Control current 300 lCTL1 (A) 200 100 0
1
2
3
4
5
0
4
8
12
16
20
Control voltage VCTL1 (V)
Control voltage VCTL1 (V)
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7. Duty - input oscillating frequency characteristic 100 Input waveform 80 60 40 20 -20 0 05 K10 K50 K100 K500 K1 M Input oscillating frequency (Hz) -40 1.9V 1.3V VCC = 6 V VFB = 1.6 V TA = +25C 40
8.Gain - frequency characteristic and phase - frequency characteristic TA = +25C 180 90 Phase 0 (deg) -90 -180 1 K 10 K100 K1 M5 M10 M f (Hz)
Duty Dtr (%)
20 Gain (dB) 0
9. Power dissipation - ambient temperature characteristic 1000 Circuit for measuring gain - frequency characteristic and phase - frequency characteristic 2.5 V 800 Power 600 dissipation PD (mW) 400 in 4.7 k 10 F -+ 4.7 k out + Error amplifier 200 4.7 k 4.7 k 2.5 V 240 k VCC = 6 V
0 -20 020 4060 80 100 Ambient temperature TA (C)
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HOW TO SET OUTPUT VOLTAGE
VREF VOUT VOUT = R R1 VREF 2 x R2 (R1 + R2)
+ -
R
R2 RNF
Note: Set the output voltage in the positive range (VOUT > 0).
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HOW TO SET OUTPUT CURRENT
The output circuit is configured in a push-pull type as shown in Figure 1. The ON current value of the output current waveform shown in Figure 2 is a constant current and the OFF value set by RE is set by a time constant. Each output current can be calculated from the following expression: * ON current = 1.5/RE (A) (Output current setting pin voltage: VE 1.5 V) * The OFF current time constant is proportional to the value of CB.
Drive Tr ON current
CB
OFF current setting part
OFF current
Output 0 current OFF current
ON current
RE
VE t
Fig.1 Output Circuit Diagram
Fig.2 Output Current Waveform
1000 pF 4 5 1
VCC 22 H Vout 10 F
-IN1 (C) (5 V) 8.2 k 2.7 k
Iout MB3788 2 1000 pF 3 150
-IN1 (E)
Fig.3 Output Pin Voltage and Current Waveforms (Channel 1)
Fig.4 Measurement Circuit Diagram
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HOW TO SET TIME CONSTANT FOR TIMER & LATCH-TYPE SHORT-CIRCUIT PROTECTION CIRCUIT
If the load conditions of the switching regulator are stable, the outputs of comparators 1 and 2 do not change, so the SP comparator outputs a High level. At this time, the SCP pin (pin 15) is held at about 50 mV. If the load conditions change suddenly due to a load short-circuit, for example, the output voltage of the comparator of the channel becomes a High-level signal (more than 2.1 V). Then, the SVP comparator outputs a Low level and transistor Q1 is turned off. The short-circuit protection capacitor CPE externally connected to the SCP pin starts to charge. VPE = 50 mV + tPE x 10-6/CPE 0.65 = 50 mV + tPE x 10-6/CPE CPE = tPE /0.6 (s) Once the capacitor CPE is charged to about 0.65 V, the SR latch is set and the output drive transistor is turned off. At this time, the duty cycle is made low and the output voltage of the SCP pin (pin 15) is held at Low level. This closes the SR latch input to discharge CPE.
2.5 V
1 A
15
S
R Low PWM input voltage comparator protection circuit OUT
Comparator 1 Comparator 2
+
Q2 Q1
CPE
SR latch-type circuit
2.1 V
Fig. 5 Latch-Type Short-Circuit Protection Circuit
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PROCESSING WITHOUT USING SCP PIN
If the timer and latch-type short-circuit protection circuit is not used, connect the SCP pin (pin 15) to GND as close as possible. Also, connect the input pin of each channel comparator to the VCC pin (pin 11).
11
VCC
9
-IN1 (C)
16
-IN2 (C)
SCP
15
GND
24
Fig. 6 Processing without using SCP Pin
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MB3788
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EQUIVALENT SERIES RESISTANCE OF SMOOTHING CAPACITOR AND STABILITY OF DC/DC CONVERTER
The equivalent series resistance (ESR) of the smoothing capacity in a DC/DC converter has a great effect on the loop phase characteristics. The ESR causes a small delay at the capacitor with a series resistance of 0 (Figures 8 and 9), thus improving system stability. On the other hand, using a smoothing capacitor with a low ESR reduces system stability. Therefore, attention should be paid to using semiconductor electrolytic capacitors (such as OS capacitors) or tantalum capacitors with a low ESP (Phase margin reduction by using an OS capacitor is explained on . the next page.)
Tr
L
RC VIN D C RL
Fig. 7 Basic Voltage-Drop Type DC/DC Converter Circuit
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0
0 (2) Gain -20 (dB) -40 (1): RC = 0 (2): RC = 31 m (2) Phase -90 (deg) (1): RC = 0 (2): RC = 31 m -180 (1)
(1)
-60 101001 k 10 k100 k Frequency f (Hz)
101001 k 10 k100 k Frequency f (Hz)
Fig.8 Gain - Frequency Characteristic
Fig.9 Phase - Frequency Charecteristic
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MB3788
(Reference Data) The phase margin is halved by changing the smoothing capacitor from an aluminum electrolytic capacitor (Rc = 1.0 ) to a semiconductor electrolytic capacitor (OS capacitor: Rc = 0.2 ) with a low ESR (Figures 11 and 12).
VOUT
VO+
CNF + VREF/2 Error amplifier -IN
+IN
R2 R1
AV - characteristic between VOUT and VIN VIN
FB
Fig. 10 DC/DC Converter AV - Characteristic Measurement Diagram
Aluminum electrolytic capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output) 60 VCC = 10 V RL = 25 180 CP = 0.1 F 40 AV 90 VO+ 20 Gain + 62 (dB) Phase 0 (deg) 0 -20 -40 101001 k 10 k 100 k Frequency f (Hz) Fig. 11 Gain - Frequency Characteristic -90 -180 GND Aluminum electrolytic capacitor 220 F (16 V) Rc 1.0 : fOSC = 1 kHz
OS capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output) 60 AV 40 20 Gain (dB) 0 -20 -40 101001 k 10 k 100 k Frequency f (Hz) Fig.12 Phase - Frequency Characteristic Curves VCC = 10 V RL = 25 CP = 0.1 F 27 180 90 0 Phase (deg) + GND OS capacitor 22 F (16 V) Rc 1.2 : fOSC = 1 kHz VO+
-90 -180
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APPLICATION CIRCUIT
10 H VCC + + -
33 F
11
33 F
13
14
CTL1 CTL2 4.7 k
8
VCC
+IN1 (E)
Cb1 Ca1
4
1000 pF (a) 22 H 5V + 150 (15 mA) 10 F
4.7 k (a) 8.2 k
7
5
-IN1 (E)
2.7 k 0.22 F
100 k
6
Channel 1 (dB)
VCC(out) OUT1 VE1
1
FB1 -IN1 (C)
2
9
3
4.7 k
17
+IN2 (E) Ca2
18 20
(b) 1000 pF 22 H + 150 VE2
22
4.7 k (b) 3.8 k -IN2 (E) 100 k
19
3V
2.7 k 0.22 F
Channel 2 (deg)
Cb2 OUT2
21
23
FB2 -IN2 (C)
10 F
16
VREF
12
SCP
15
-IN(PWM)
10
GND
24
0.1 F
Triangular wave signal 1.9 V 1.3 V CT

+15 V +24 V DC motor 1 DC motor 2
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PRECAUTIONS
1. Do not apply any voltage greater than the maximum rating, or the LSI may be damaged. 2. Use the MB3788 under the recommended operating conditions. If a voltage greater than the maximum voltage is applied, the electrical characteristics are not guaranteed; if a voltage smaller than the minimum voltage is applied, the LSI operation will become unstable. 3. To ground the PC board, use the thickest cable possible because high frequencies are used which can easily produce high-frequency noise. 4. Connecting unused channel pin For unused channels, the output voltage of the comparator for detecting a short-circuit must be fixed at the Low level. 5. Take measures against static electricity. * * * * Carry semiconductors in a conductive container or anti-static case. Carry the PC board in a conductive bag or container if it is stored or transported after packaging. Ground the workbench, and all tools and measuring instruments. Workers should be grounded through a resistance of 250 k to 1 M.
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PACKAGE DIMENSION
24-pin plastic SSOP (FPT-24P-M03)
* 7.750.10(.305.004)
1.25 -0.10 .049 -.004
+0.20 +.008
(Mounting height)
0.10(.004)
* 5.600.10
INDEX (.220.004)
7.600.20 (.299.008)
6.60(.260) NOM
0.650.12(.0256.0047)
0.22 -0.05 .009
+0.10 +.004 -.002
"A"
0.15 -0.02 .006 -.001
+0.05 +.002
Details of "A" part 0.100.10(.004.004) (STAND OFF)
7.15(.281)REF
0
10
0.500.20 (.020.008)
C
1994 FUJITSU LIMITED F24018S-2C-2
Dimensions in mm (inches).
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MB3788
FUJITSU LIMITED
For further information please contact:
Japan FUJITSU MEDIA DEVICES LIMITED Marketing and Technical Support Dept. SUN HAMADA BLDG 2F 1-19-20, Shin-yokohama kouhoku-ku Yokohama-shi Kanagawa 222-0033, Japan Tel: 81(45) 471-0061 Fax: 81(45) 471-0076
All Rights Reserved. The contents of this document are subject to change without notice. Customers are advised to consult with FUJITSU sales representatives before ordering. The information and circuit diagrams in this document are presented as examples of semiconductor device applications, and are not intended to be incorporated in devices for actual use. Also, FUJITSU is unable to assume responsibility for infringement of any patent rights or other rights of third parties arising from the use of this information or circuit diagrams. FUJITSU semiconductor devices are intended for use in standard applications (computers, office automation and other office equipment, industrial, communications, and measurement equipment, personal or household devices, etc.). CAUTION: Customers considering the use of our products in special applications where failure or abnormal operation may directly affect human lives or cause physical injury or property damage, or where extremely high levels of reliability are demanded (such as aerospace systems, atomic energy controls, sea floor repeaters, vehicle operating controls, medical devices for life support, etc.) are requested to consult with FUJITSU sales representatives before such use. The company will not be responsible for damages arising from such use without prior approval. Any semiconductor devices have an inherent chance of failure. You must protect against injury, damage or loss from such failures by incorporating safety design measures into your facility and equipment such as redundancy, fire protection, and prevention of over-current levels and other abnormal operating conditions. If any products described in this document represent goods or technologies subject to certain restrictions on export under the Foreign Exchange and Foreign Trade Law of Japan, the prior authorization by Japanese government will be required for export of those products from Japan.
North and South America FUJITSU MICROELECTRONICS, INC. Semiconductor Division 3545 North First Street San Jose, CA 95134-1804, USA Tel: (408) 922-9000 Fax: (408) 922-9179 Customer Response Center Mon. - Fri.: 7 am - 5 pm (PST) Tel: (800) 866-8608 Fax: (408) 922-9179
http://www.fujitsumicro.com/
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http://www.fujitsu-ede.com/
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http://www.fmap.com.sg/
F9902 (c) FUJITSU LIMITED Printed in Japan

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