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

MB3788
11
(Continued)
VCC = 6 V
VFB = 1.6 V
TA= +25°C
100
80
60
40
20
00 5K 10K 50K 100K 500K 1M
1.9V
1.3V
Duty
Dtr (%)
Input oscillating frequency (Hz)
40
20
0
-20
-40
1K 10K 100K 1M 5M 10M
TA= +25°C180
90
0
-90
-180
Input waveform
Gain
(dB) Phase
φ(deg)
1000
800
600
400
200
0-20 020 406080 100
Power
dissipation
PD(mW)
Ambient temperature TA(°C)
7. Duty - input oscillating frequency characteristic 8.Gain - frequency characteristic and phase - frequency
characteristic
f (Hz)
9. Power dissipation - ambient temperature characteristic Circuit for measuring gain - frequency characteristic and
phase - frequency characteristic
2.5 V
-
+out
2.5 V
in +
-
10 µF
240 kΩ
4.7 kΩ
4.7 kΩ
VCC = 6 V
4.7 kΩ4.7 kΩ
Error amplifier

MB3788
12
■
■■
■HOW TO SET OUTPUT VOLTAGE
+
-
VREF VOUT
RNF
R1
R2
R
R
VOUT = (R1+ R2)
VREF
2 ×R2
Note: Set the output voltage in the positive range (VOUT > 0).

MB3788
13
■
■■
■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.
OFF current
setting part
RE
CB
Drive Tr
OFF
current
ON current
Output
current 0
ON current
OFF current
t
22 µH(5 V)
3150 Ω
1000 pF
4 5 1
VCC
Iout
1000 pF
10 µF
-IN1 (E)
8.2 kΩ
-IN1 (C)
MB3788 2
Fig.1 Output Circuit Diagram Fig.2 Output Current Waveform
Fig.3 Output Pin Voltage and Current Waveforms (Channel 1) Fig.4 Measurement Circuit Diagram
VE
2.7 kΩ
Vout

MB3788
14
■
■■
■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 com-
parator 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 ×10-6/CPE
0.65 = 50 mV + tPE ×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.
Fig. 5 Latch-Type Short-Circuit Protection Circuit
2.1 V
Low
input
voltage
protection
circuit
SR latch-type
circuit
1 µA
CPE
-
-
+
OUT
2.5 V
15
Q2
Q1
Comparator 1
Comparator 2
SR
PWM
comparator

MB3788
15
■
■■
■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).
Fig. 6 Processing without using SCP Pin
24
9-IN1 (C)
VCC
16 -IN2 (C)
15 GND
SCP
11

MB3788
16
■
■■
■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.)
L
Tr
RC
RLVIN D
C
20
0
-20
-40
-60
10 100 1k 10k 100k
0
-90
-180
10 100 1k 10k 100k
(2)
(1)
(1): RC= 0 Ω
(2): RC = 31 mΩ
(2)
(1)
Gain
(dB)
Frequency f (Hz) Frequency f (Hz)
Phase
(deg)
(1): RC= 0 Ω
(2): RC= 31 mΩ
Fig. 7 Basic Voltage-Drop Type DC/DC Converter Circuit
Fig.8 Gain - Frequency Characteristic Fig.9 Phase - Frequency Charecteristic

MB3788
17
(Reference Data)
The phase margin is halved by changing the smoothing capacitor from an aluminum electrolytic capacitor (Rc
=1.0Ω)toasemiconductorelectrolyticcapacitor(OScapacitor: Rc =0.2Ω)withalowESR(Figures11and12).
Fig. 10 DC/DC Converter AV - φ
φφ
φCharacteristic Measurement Diagram
Fig. 11 Gain - Frequency Characteristic
Fig.12 Phase - Frequency Characteristic Curves
+
-
AV- φcharacteristic between VOUT and VIN
Error amplifier
VOUT
CNF
FB VIN
R2
R1
VO+
-IN
+IN
VREF/2
62°
AVϕ⇒
101001 k10 k100 k
60
40
20
0
-20
-40
180
90
0
-90
-180
VCC = 10 V
RL = 25 Ω
CP = 0.1 µF
Gain
(dB)
Frequency f (Hz)
Aluminum electrolytic capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output)
Aluminum electrolytic capacitor
220 µF (16 V)
Rc ≈1.0 Ω: fOSC = 1 kHz
VO+
+
-
Phase
(deg)
GND
AV
ϕ⇒
101001 k10 k100 k
60
40
20
0
-20
-40
180
90
0
-90
-180
27°
VCC = 10 V
RL = 25 Ω
CP = 0.1 µF
Gain
(dB)
Frequency f (Hz)
OS capacitor gain - frequency and phase - frequency characteristics (DC/DC converter +5 V output)
OS capacitor
22 µF (16 V)
Rc ≈1.2 Ω: fOSC = 1 kHz
VO+
+
-
GND
Phase
(deg)

MB3788
18
■
■■
■APPLICATION CIRCUIT
+15 V
+24 V
DC motor 1
DC motor 2
24
150 Ω
23
20
21
22
1000 pF
Channel 1
(dB)
<Logic power supply>
(b)
22 µH3 V
10 µF
Ca2
Cb2
OUT2
VE2
150 Ω
1000 pF <Logic power supply>
+
(a)
22 µH5 V
10 µF
Ca1
VCC(out)
OUT1
VE1
2
3
5
1
4
Cb1
(15 mA)
Channel 2
(deg)
10 µH
+
-33 µF
+
-33 µF
VCC
11
6
9
7
8
-IN1 (E)
FB1
-IN1 (C)
+IN1 (E)
VCC
14
CTL2
13
CTL1
(a) 4.7 kΩ
4.7 kΩ
8.2 kΩ
2.7 kΩ100 kΩ
19
16
18
17
-IN2 (E)
FB2
-IN2 (C)
+IN2 (E)
(b) 4.7 kΩ
4.7 kΩ
3.8 kΩ
2.7 kΩ100 kΩ
15 10
12 GND-IN(PWM)SCPVREF
⇑
Triangular wave signal
1.9 V
1.3 V
CT
<MB3785A-used DC/DC converter>
<Analog power supply>
<Sensor power supply>
<DC motor speed control>
<DC motor speed control>
-
+
-
0.1 µF
0.22 µF
0.22 µF

MB3788
19
■
■■
■NOTES ON USE
• Take account of common impedance when designing the earth line on a printed wiring board.
• Take measures against static electricity.
- For semiconductors, use antistatic or conductive containers.
- When storing or carrying a printed circuit board after chip mounting, put it in a conductive bag or container.
- The work table, tools and measuring instruments must be grounded.
- The worker must put on a grounding device containing 250 kΩto 1 MΩresistors in series.
• Do not apply a negative voltage
- Applying a negative voltage of −0.3 V or less to an LSI may generate a parasitic transistor, resulting in
malfunction.
■
■■
■ORDERING INFORMATION
Part number Package Remarks
MB3788PFV 24-pin Plastic SSOP
(FPT-24P-M03)

MB3788
20
■
■■
■PACKAGE DIMENSION
24-pin plastic SSOP
(FPT-24P-M03)
Note 1) *1 : Resin protrusion. (Each side : +0.15 (.006) Max) .
Note 2) *2 : These dimensions do not include resin protrusion.
Note 3) Pins width and pins thickness include plating thickness.
Note 4) Pins width do not include tie bar cutting remainder.
Dimensions in mm (inches) .
Note : The values in parentheses are reference values.
C
2003 FUJITSU LIMITED F24018S-c-4-5
7.75±0.10(.305±.004)
5.60±0.10 7.60±0.20
(.220±.004) (.299±.008)
*1
*2
0.10(.004)
112
1324
0.65(.026) –0.07
+0.08
0.24
.009 +.003
–.003 M
0.13(.005)
INDEX
0.17±0.03
(.007±.001)
"A"
0.25(.010)
0.10±0.10
(.004±.004)
(Stand off)
Details of "A" part
(Mounting height)
1.25 +0.20
–0.10
–.004
+.008
.049
0~8˚
0.50±0.20
(.020±.008)
0.60±0.15
(.024±.006)
0.10(.004)