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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.
s FEATURES
* * * * * * * * * 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
(FPT-16P-M05)
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
-IN1 *1 +IN1 *1
7
10
-IN2 *2 +IN2 *2
8
9
(FPT-16P-M05) *1: Pins on error amplifier 1 *2: Pins on error amplifier 2
2
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
4 1 14 2 16
SYNC VCC1 VCC2 VREF GND
I -- -- O --
External sync signal input pin Reference power supply, control circuit power-supply pin Output circuit power-supply pin Reference voltage output pin Ground pin
Power-supply circuit
3
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 k
-0.9 V 8 A SCP comparator 1 4 A -0.3 V
1.25 V 1.25 V 2 A SCP comparator 2 VCC1 1 1.1 V VREF 2 Reference Power voltage ON/OFF supply circuit 1.8 V SR latch Under voltage Lock-out protection circuit Sawtooth wave oscillator SCP comparator 3 VREF
16 GND
5 SCP External sync signal SYNC
4
3 CT
4
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 A, 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 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 comparator with one inverting input and three noninverting inputs, serving as a voltage-pulse width converter for controlling the output duty depending on the input voltage. The PWM comparator turns on the output transistor during the interval in which the sawtooth wave voltage level is lower than the voltage levels at all of the error amplifier output pins, the SCP pin (pin 5), and at the DTC pin (pin 12). (5) Output circuit The output circuit is a power MOSFET driven, output circuit in a totem-pole configuration. It can drive the gate voltage up to near the supply voltage with a bootstrap capacitor connected between the OUT pin (pin 15) and CB pin (pin 13). (See "s SETTING THE BOOTSTRAP CAPACITOR (CBS).")
2. Protection Functions
(1) Timer-latch short-circuit protection circuit SCP comparator 1 detects the output voltage levels of error amplifiers 1 and 2. When the output voltage level of either (or both) of the two error amplifiers reaches 1.25 V, the timer circuit is actuated to start charging the external protection-enable capacitor connected to the SCP pin (pin 5). If the error amplifier output is not restored to the normal voltage level before the capacitor voltage reaches 1.8 V, the latch circuit is actuated to turn off the output transistor while making the dead time 100%. To reset the actuated protection circuit, turn the power supply on back. (See "s SETTING THE SOFT START/ SHORT-CIRCUIT DETECTION TIME.")
5
MB3789
(2) Low input voltage malfunction preventive circuit The transient state or a momentary decrease in supply voltage, which occurs when the power supply is turned on, may cause errors in the control IC, resulting in breakdown or degradation of the system. The low input voltage malfunction preventive circuit detects the internal reference voltage level according to the supply voltage level and, if the input voltage is low, turn off the output transistor and maintains the SCP pin (pin 5) at 0 V while making the dead time 100%. The circuit restores voltage supply when the supply voltage reaches its threshold voltage.
6
MB3789
s ABSOLUTE MAXIMUM RATINGS
(Ta = +25C) Parameter Power supply voltage Power dissipation Operating temperature Storage temperature Symbol VCC PD Top Tstg Ta Condition -- +25C -- -- Rating Min. -- -- -30 -55 Max. 20 440* +85 +125 Unit V mW C C
* : When mounted on a 10 cm-square double-side epoxy board. 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.
s RECOMMENDED OPERATING CONDITIONS
(Ta = +25C) Parameter Power supply voltage Reference voltage output current Error amp. input voltage Output current IO- Timing resistance Timing capacitance Oscillation frequency Operating temperature RT CT fOSC TOP Symbol VCC1 VCC2 IOR VI IO+ -- -- CB = 4700 pF, t 2 s CB = 4700 pF, t 2 s -- -- -- -- Condition -- Value Min. 3.0 -- -50 -0.2 -70 -- 10 470 1 -30 Typ. 5.0 6.0 -30 -- -40 40 39 1000 20 +25 Max. 18 18 -- VCC - 1.8 -- 70 200 6800 200 +85 Unit V V A V mA mA k pF kHz C
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.
7
MB3789
s ELECTRICAL CHARACTERISTICS
(VCC1 = 5 V, VCC2 = 6 V, Ta = +25C) Parameter Output voltage Output voltage temperature variation Input stability Load stability Short output current Under voltage lockout protection circuit Soft start block Threshold voltage Hysteresis width Reset voltage (VCC) Charge current Threshold voltage Threshold voltage Short circuit detection block Input standby voltage Input latch voltage Input source current Oscillator frequency Frequency voltage variation Triangular waveform oscillator block Frequency temperature variation Synchronous pin input current Synchronous pin threshold voltage * : Standard design value Symbol VREF Condition IOR = 0 A Value Min. 2.400 -- -- -- -700 -- 1.62 80 1.0 -2.8 0.2 0.8 1.70 1.15 -- -8.4 17 -- -- 0.9 0.65 Typ. 2.500 0.2 1 2 -450 2.15 1.90 250 1.4 -2.0 0.3 0.9 1.80 1.25 50 -6.0 20 1 3 1.3 0.75 Max. 2.600 2 10 10 -300 2.62 -- -- -- -1.2 0.4 1.0 1.90 1.35 100 -3.6 23 10 -- 2.2 0.85 Unit V % mV mV A V V mV V A V V V mV mV A kHz % % mA V
Reference voltage block
VREF/VREF Ta = -30C to +85C* Line Load IOS VTH VTL VHYS VR ICHG VT0 VT100 VTH VSTB VI II fOSC f/fdv f/fdT ISYNC VTHSY VCC = 3.0 V to 18 V IOR = 0 A to -50 A VREF = 0 V -- -- -- -- VSCP 0.9 V Duty cycle = 0% Duty cycle = 100% -- -- -- VSCP = 1.5 V CT = 1000 pF, RT = 39 k VCC = 3 V to 18 V Ta = -30C to +85C* VTHSY = 5 V --
(Continued)
8
MB3789
(Continued)
(VCC1 = 5 V, VCC2 = 6 V, Ta = +25C) Parameter Input offset voltage Input offset current Input bias current Common mode input voltage range Common mode rejection ratio Error amplifier Voltage gain Frequency bandwidth Maximum output voltage range Output sink current Output source current Threshold voltage Dead time control block ON duty cycle Input bias current PWM comparator block Threshold voltage Input sink current Input source current Output block Output voltage VOL General Power supply current when output off ICC1 ICC2 Symbol VIO IIO IB VCM CMRR AV BW VOM+ VOM- IOM+ IOM- VT0 VT100 Dtr IIbdt VT0 VT100 IIN+ IIN- VOH Condition VFB = 0.6 V VFB = 0.6 V VFB = 0.6 V -- -- -- AV = 0 dB* -- -- VFB = 0.6 V VFB = 0.6 V Duty cycle = 0% Duty cycle = 100% Vdt = VREF/4.2 -- Duty cycle = 0% Duty cycle = 100% -- -- CL = 2000 pF, CB = 4700 pF CL = 2000 pF, CB = 4700 pF -- -- Value Min. -- -- -200 -0.2 60 60 -- VREF - 0.3 -- 30 -- 0.2 0.8 45 -500 0.2 0.8 30 -- 5.5 -- -- -- Typ. -- -- -30 -- 100 100 800 2.4 0.05 60 -2 0.3 0.9 55 -100 0.3 0.9 60 -2 6.0 1.1 1.15 350 Max. 10 100 -- VCC - 0.8 -- -- -- -- 0.3 -- -0.6 0.4 1.0 65 -- 0.4 1.0 -- -0.6 -- 1.4 1.65 500 Unit mV nA nA V dB dB kHz V V A mA V V % nA V V A mA V V mA A
* : Standard design value
9
MB3789
s TYPICAL CHARACTERISTICS
Power supply current vs. power supply voltage characteristics
2.4 2.0 1.6 1.2 0.8 0.4 0 0 4 8 12 16 20 Power supply voltage VCC1 (V) VCC2 = 6 V Ta = +25C Output power supply current ICC1 (A) 500 VCC1 = 5 V Ta = +25C 400
Output power supply current vs. power supply voltage characteristics
Power supply current ICC1 (mA)
300
200
100
0 0 4 8 12 16 20 Power supply voltage VCC2 (V)
Reference voltage vs. power supply voltage characteristics
5.0 VCC2 = 6 V IOR = 0 A Ta = +25C 2.56 2.54 Reference voltage VREF (V) 2.52 2.50 2.48 2.46 2.44 0 0 4 8 12 16 20 Power supply voltage VCC1 (V)
Reference voltage vs. ambient temperature characteristics
Reference voltage VREF (V)
4.0
VCC1 = 5 V VCC2 = 6 V IOR = 0 A
3.0
2.0
1.0
-40
-20
0
20
40
60
80
100
Ambient temperature Ta (C)
Sawtooth waveform maximum amplitude voltage vs. timing capacitance characteristics (With CT/RT oscillation)
1.4 1.2 Sawtooth waveform maximum amplitude voltage VCT (V) 1.0 0.8 0.6 0.4 0.2 0 10 2 5 x 102 103 5 x 103 104 5 x 104 Timing capacitance CT (pF) VCC1 = 5 V VCC2 = 6 V RT = 39 k SYNC = GND Ta = +25C 500 k
Sawtooth wave frequency vs. timing resistance characteristics (With CT/RT oscillation)
VCC1 = 5 V VCC2 = 6 V SYNC = GND Ta = +25C
Sawtooth wave frequency f (Hz)
100 k 50 k
10 k 5k
CT = 470 pF
1k 500
CT = 1500 pF CT = 4700 pF CT = 6800 pF
100 2k
5k
10 k
50 k 100 k
500 k 1 M
Timing resistance RT ()
(Continued)
10
MB3789
Sawtooth waveform period vs. timing capacitance characteristics (With CT/RT oscillation)
500 Sawtooth waveform period t (s) 100
Duty vs. sawtooth wave frequency characteristics (With CT/RT oscillation)
VCC1 = 5 V VCC2 = 6 V VDT = 0.6 V CT = Variable RT = 39 k SYNC = GND Ta = -25C
100 50
Duty (%)
4
VCC1 = 5 V VCC2 = 6 V RT = 39 k SYNC = GND Ta = +25C
80
60
40
10 5 20
2 2 2 3 2 x 10 5 x 10 10 5 x 10 10
5 x 10
3
10
4
5 x 10
0 200 500 1 k 5 k 10 k 50 k 100 k 500 k Sawtooth wave frequency f (Hz)
Timing capacitance CT (pF)
Sawtooth wave frequency vs. ambient temperature characteristics (With CT/RT oscillation)
VCC1 = 5 V VCC2 = 6 V CT = 1500pF RT = 39 k SYNC = GND
Sawtooth wave frequency vs. ambient temperature characteristics (In external synchronization)
VCC1 = 5 V VCC2 = 6 V CT = 1500pF RT = 43 k fSYNC = 15.0 kHz
Frequency regulation f/f (%)
Frequency regulation f/f (%)
+10 +5 0 -5 -10
+10 +5
0 -5 10
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
Ambient temperature Ta (C)
Ambient temperature Ta (C)
Gain vs. frequency and phase vs. frequency characteristics
40 VCC1 = 5 V VCC2 = 6 V Ta = +25C Av 180
Measurement circuit for gain-frequency characteristics and phase-frequency characteristics
2.5 V 2.5 V
20 Gain AV (dB)
90 Phase (deg)
4.7 k
4.7 k
240 k
0
0
10 F IN 4.7 k 4.7 k Error amp.
OUT
-20
-90
-40 1k 10 k 100 k Frequency f (Hz) 1M
-180 10 M
(Continued)
11
MB3789
(Continued)
Duty vs. DTC pin voltage characteristics
100 VCC1 = 5 V VCC2 = 6 V CT = 1500 pF RT = 39 k SYNC = GND
Output pin (OUT) voltage and current waveforms
VCC1 = 5 V, VCC2 = 6 V 6 4 2 Output current IO (mA) 100 50 0 -50 -100 0 4 8 12 Time t (s) 16 20 0 Output voltage VOUT (V)
80
Duty (%)
60
40
20
0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 DTC pin voltage Vdt (V)
Power comsumption vs. ambient temperature characteristics
500 440 Power comsumption PD (mW) 400
300
200
100
0 -30 -20
0
20
40
60
80
100
Ambient temperature Ta (C)
12
MB3789
s SETTING THE OUTPUT VOLTAGE
Set the output voltage by connecting the input pins (+IN, -IN) and output pin (FB) of error amplifiers 1 and 2 as shown in Figures 1 and 2.
VREF VOUT + VREF + VOUT = 2 x R2
R
R1
(R1 + R2)
R
R2
RNF
Figure 1 Setting the output voltage (positive output voltage (VOUT))
VREF
R
R1
VOUT- = -
VREF 2 x R1
(R1 + R2) + VREF
R
R2 RNF VOUT-
Figure 2 Setting the output voltage (negative output voltage (VOUT))
13
MB3789
s CONNECTION FOR OUTPUT CONTROL WITH ONE ERROR AMPLIFIER
The MB3789 can make up a system using only one of the two error amplifiers. In this case, connect the +IN and -IN pins of the unused error amplifier to the VREF and GND pins, respectively, and leave the FB pin open. When VCC - 1.8 V < VREF, divide the VREF voltage using a resistor and apply the voltage to the +IN pin.
VREF 2 +IN1 8 -IN1 7 FB1 6 "Open"
Figure 1 Connection without using error amplifier 1
VREF 2 +IN2 9 -IN2 10 FB2 11 "Open"
Figure 2 Connection without using error amplifier 2
14
MB3789
s CONNECTING THE SAWTOOTH WAVEFORM OSCILLATOR
1. Connection for internal oscillation
For internal oscillation, connect the frequency setting capacitor (CT) and resistor (RT) to the CT pin (pin 3) and leave the SYNC pin (pin 4) open or connect it to GND. The oscillation frequency can be set with the CT and RT constants.
CT 3
SYNC 4
CT
RT Leave "open" or connect to GND
Figure 5 Connection for internal oscillation
2. Connection for external synchronous oscillation
For external synchronous oscillation, connect the frequency setting capacitor (CT) and resistor (RT) to the CT pin (pin 3) and connect the external sync signal to the SYNC pin (pin 4). In this case, select the CT and RT conditions so that the oscillation frequency is 5% to 10% lower than the frequency of the external sync signal excluding the setting error of the oscillation frequency.
CT 3
SYNC 4
External sync signal CT RT
Figure 6 Connection for external synchronous oscillation
15
MB3789
s SETTING THE DEAD TIME
When the device is set for step-up inverting output based on the flyback method, the output transistor is fixed to a full-ON state (ON duty = 100%) when the power supply is turned on. To prevent this problem, you may determine the voltage at the DTC pin (pin 12) from the VREF voltage so you can set the output transistor's dead time (maximum ON-duty period) as shown in Figure 7 below.
1. Setting the dead time
When setting the dead time, use resistors as shown in Figure 7 to connect the VREF and DTC pins to GND. When the voltage at the DTC pin (pin 12) is lower than the sawtooth wave output voltage from the oscillator, the output transistor is turned off. To set the dead time, see "Duty vs. DTC pin voltage" (in "s STANDARD CHARACTERISTIC CURVES"). Vdt = R2 x VREF R1 + R2
2. Connection without setting the dead time
If you do not set the dead time, connect the VREF and DTC pins as shown in Figure 8.
2 VREF R1 12 DTC Vdt R2
Figure 7 Connection for setting the dead time
2 VREF
12 DTC
Figure 8 Connection without setting the dead time
16
MB3789
s SETTING THE SOFT START/SHORT-CIRCUIT DETECTION TIME
Connecting capacitor CPE to the SCP pin (pin 5) as shown in Figure 9 enables a soft start and short-circuit protection.
SCP comparator 1
8 A
4 A
1.25 V SCP comparator 3 1.25 V SCP comparator 2 1.1 V 2 A 1.8 V SR latch VREF
Output OFF
Low input voltage protection circuit
5 SCP CPE
Figure 9 Soft start/short-circuit detection circuit
2 1.8 V
SCP pin voltage (V)
1.25 V Output short-circuit 1 100% Output short-circuit tPE
50%
0%
ts Soft start Time t (s)
0
Figure 10 SCP pin operating waveform
17
MB3789
1. Soft Start
To prevent surge currents when the IC is turned on, you can set a soft start by connecting capacitor CPE to the SCP pin (pin 5). * Softstart time(ts): Time required up to duty cycle ~ 50% with output on tS (s) ~ 0.15 x CPE (F)
2. Protection from short circuit
SCP comparator 1 always compares the output voltage levels at error amplifiers 1 and 2 with the 1.25 V reference voltage. When the load conditions for the switching regulator are stable, the outputs from error amplifiers 1 and 2 do not vary and thus short-circuit protection control remains balanced. In this case, the SCP pin (pin 5) is held at the soft start end voltage (about 1.25 V). If the load conditions change rapidly and the output voltage of error amplifier 1 or 2 reaches 1.25 V, for example, because of a short-circuit of a load, capacitor CPE is charged further. When capacitor CPE is charged up to about 1.8 V, the SR latch is set and the output drive transistor is turned off. At this time, the dead time is set to 100%, capacitor CPE is discharged, and the SCP pin becomes ~ 50 mV. * Short-circuit detection time (tPE) tPE (s) ~ 0.09 x CPE (F)
3. Connection without using short-circuit protection
Add a clamp circuit as shown in Figure 11 so that the clamp voltage (VCRP) falls within the following range when a short-circuit is detected: 1.0 V < VCRP < 1.7 V
Clamp circuit 5 SCP
VCRP
CPE
Figure 11 Connection without using short-circuit protection
18
MB3789
s SETTING THE BOOTSTRAP CAPACITOR
When a bootstrap capacitor is connected, it raises the output-ON voltage (at the OUT pin (pin 15) when the external MOS FET is turned "ON") to the ~ VCC2 level. It can therefore drive the MOS FET at a higher threshold voltage (Vth).
1. Connecting the bootstrap capacitor
Connect the bootstrap capacitor between the CB pin (pin 13) and OUT pin (pin 15).
VCBS
VCC2
id 13 CB
14
VCC2
VCC1 CBS
iC I 15 OUT 10 k External MOS FET
VOUT
: Charge current ic : Discharge current id
Figure 12 Circuit with a bootstrap capacitor connected and current flow * Calculation of bootstrap capacitance CBS 500 x 106 x tON (max) [pF] VCC2 - 2.6
tON (max): Maximum ON duty time
19
MB3789
2. Connection with no bootstrap capacitor
Connect the CB pin (pin 13) and VCC2 pin (pin 14) as shown in Figure 13.
VCC2
CB 13
VCC2 14
OUT 15
External MOS FET
Note: Under a condition of "VCC2 - Vth < 1.1 V", bootstrap capacitor CBS should be connected because the external MOS FET cannot be driven sufficiently. Vth: External MOS FET threshold voltage
Figure 13 Connection with no bootstrap capacitor connected
20
MB3789
3. Operation of the Bootstrap Capacitor
When voltage VOUT at the OUT pin (pin 15) is "L" level, the voltages (VC1) at both ends of the bootstrap capacitor CBS is charged up to the VCC2 voltage level by charge current (iC). When VOUT changes from "L" level to "H" level, the CB pin (pin 13) voltage VCBS rises to ~ 2 x VCC2 and VOUT reaches almost the VCC2 level. The charge accumulated at CBS at this time is released by discharge current id (output unit supply current). See Figure 12 for circuit operation.
(VCC1 = 5 V, VCC2 = 6 V, CBS = 4700 pF) 2V 12
*2
8 OUT pin voltage VOUT (V) VCBS *1 6 4 2 0 2V 0 20 40 60 10 s 80 100 6 4 2 VOUT 0
tON
tOFF Time t (s)
*1: Use the device with a setting of VCBS 18 V. *2: The slant of VCBS is determined by the value of discharge current id (output unit supply current).
Figure 14 Bootstrap operating waveform
CB pin voltage VCBS (V)
10
21
MB3789
s EQUIVALENT SERIES RESISTANCE OF SMOOTHING CAPACITOR AND SYSTEM STABILITY
The equivalent series resistance (ESR) value of a smoothing capacitor for the DC/DC converter largely affects the loop phase characteristic. Depending on the ESR value, the phase characteristic causes the ideal capacitor in a high-frequency domain advance the loop phase (as shown in Figures 16 and 17) and thus the system is improved in stability. In contrast, using a smoothing capacitor with low ESR lowers system stability. Use meticulous care when a semiconductor electrolytic capacitor with low ESR (such as an OS capacitor) or a tantalum capacitor is used. (The next page gives an example of reduction in phase margin when an OS capacitor is used.)
Tr
L
RC VIN D C RL
Figure 15 Basic circuit of step-down DC/DC converter
20
0
Phase (deg)
0 Gain (dB) -20 -40 -60 10 (1) : RC = 0 (2) : RC = 31 m 100 1k Frequency f (Hz) (1) 10 k 100 k
(2) -90
(2)
(1) : RC = 0 (2) : RC = 31 m -180
(1)
10
100
1k Frequency f (Hz)
10 k
100 k
Figure 16 Gain vs. frequency
Figure 17 Phase vs. frequency
22
MB3789
(Reference data) Changing the smoothing capacitor from an aluminum electrolytic capacitor (RC ~ 1.0 ) to a low-ESR semiconductor electrolytic capacitor (OS capacitor: RC ~ 0.2 ) halves the phase margin. (See Figures 19 and 20.)
VOUT VO +
CNF
AV-phase characteristic in this range -IN VIN
FB
+IN R1
R2
VREF/2 Error amplifier
Figure 18 DC/DC converter Av vs. phase measurement diagram
AI electrolytic capacitor gain vs. frequency, phase vs. Frequency (DC/DC converter +5 V output)
60 40 AV Gain (dB) 20 0 -20 -40 10 62 VCC = 10 V RL = 25 CP = 0.1 F 180 90 0 Phase (deg) VO + AI electrolytic capacit 220 F (16 V) RC 1.0 : fOSC = 1 kHz GND
-90 -180 100 k
100
1k Frequency f (Hz)
10 k
Figure 19 Gain vs. frequency
23
MB3789
OS capacitor gain vs. frequency, phase vs. frequency (DC/DC converter +5 V output)
60 AV 40 Gain (dB) 20 0 -20 -40 10 27 0 VCC = 10 V RL = 25 CP = 0.1 F 180 90 Phase (deg)
VO + OS capacitor 22 F (16 V) RC 0.2 : fOSC = 1 kHz GND
-90 -180 100 k
100
1k Frequency f (Hz)
10 k
Figure 20 Phase vs. frequency characteristic curves
24
MB3789
s APPLICATION EXAMPLE
VCC (5 V) 2 VREF 8 +IN1 100 k 7 -IN1 2.7 k 100 k 6 FB1 150 k 9 +IN2 100 k 10 -IN2 10 k 100 k 11 FB2 150 k 12 DTC 100 k SYNC 4 33 pF CT 3 MB3789
10 F
10 H
100 k 18 k
1 VCC1 VCC2 14
CB 13
4700 pF
OUT 15
Back light
GND 16 SCP 5 4.7 F
10 F
39
1 F
22 k
1500 pF 4.7 k Synchronous signal 33 k
25
MB3789
s USAGE PRECAUTIONS
1. Do not input voltages greater than the maximum rating.
Inputting voltages greater than the maximum rating may damage the device.
2. Always use the device under recommended operating conditions.
If a voltage greater than the maximum value is input to the device, its electrical characteristics may not be guaranteed. Similarly, inputting a voltage below the minimum value may cause device operation to become unstable.
3. For grounding the printed circuit board, use as wide ground lines as possible to prevent high-frequency noise.
Because the device uses high frequencies, it tends to generate high-frequency noise.
4. Take the following measures for protection against static charge:
* * * * For containing semiconductor devices, use an antistatic or conductive container. When storing or transporting device-mounted circuit boards, use a conductive bag or container. Ground the workbenches, tools, and measuring equipment to earth. Make sure that operators wear wrist straps or other appropriate fittings grounded to earth via a resistance of 250 k to 1 M placed in series between the human body and earth.
s ORDERING INFORMATION
Part number MB3789PFV Package 16-pin Plastic SSOP (FPT-16P-M05) Remarks
26
MB3789
s PACKAGE DIMENSION
16-pin Plastic SSOP (FPT-16P-M05)
*: These dimensions do not include resin protrusion.
* 5.000.10(.197.004)
1.25 -0.10 +.008 .049 -.004
+0.20
(Mounting height)
0.10(.004)
INDEX
*4.400.10
(.173.004)
6.400.20 (.252.008)
5.40(.213) NOM
0.650.12 (.0256.0047)
0.22 -0.05 +.004 .009 -.002
+0.10
"A"
0.15 -0.02 +.002 .006 -.001
+0.05
Details of "A" part 0.100.10(.004.004) (STAND OFF)
4.55(.179)REF
0
10
0.500.20 (.020.008)
C
1994 FUJITSU LIMITED F16013S-2C-4
Dimensions in mm (inches)
27
MB3789
FUJITSU LIMITED
For further information please contact:
Japan FUJITSU LIMITED Corporate Global Business Support Division Electronic Devices KAWASAKI PLANT, 4-1-1, Kamikodanaka Nakahara-ku, Kawasaki-shi Kanagawa 211-8588, Japan Tel: 81(44) 754-3763 Fax: 81(44) 754-3329
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.
http://www.fujitsu.co.jp/
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/
Europe FUJITSU MIKROELEKTRONIK GmbH Am Siebenstein 6-10 D-63303 Dreieich-Buchschlag Germany Tel: (06103) 690-0 Fax: (06103) 690-122
http://www.fujitsu-ede.com/
Asia Pacific FUJITSU MICROELECTRONICS ASIA PTE LTD #05-08, 151 Lorong Chuan New Tech Park Singapore 556741 Tel: (65) 281-0770 Fax: (65) 281-0220
http://www.fmap.com.sg/
F9906 (c) FUJITSU LIMITED Printed in Japan
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