FUJITSU SEMICONDUCTOR DS04-27209-3E 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%.
MB3788 (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 V - 1.8 V • On-chip high-accuracy reference voltage circuit: 2.50 V 1% •...
MB3788 PIN DESCRIPTION Pin No. Pin name Descriptions OUT1 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. —...
MB3788 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 V pin (pin12).
MB3788 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.
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.
MB3788 ELECTICAL CHARACTERISTICS =6V, T = +25 C) Value Parameter Symbol Conditions Unit = -1 mA Reference voltage 2.475 2.500 2.525 Output voltage temperature = -30 to +85 C variation Reference voltage Input stability Line = 3.6 V to 18 V —...
MB3788 (Continued) Values Parameter Symbol Conditions Unit Duty cycle = 0 % 1.05 — Threshold voltage Duty cycle = 100 % — 2.25 t100 Input sink current — — — comparator Input source current — — — Input bias current = 0 V -1.0 -0.5...
MB3788 STANDARD CHARACTERISTIC CURVES 1. Power current - supply voltage characteristic 2. Reference voltage - supply voltage characteristic = +25 C = +25 C CTL1 = 6 V CTL1, 2 = 6 V Reference Power voltage current REF ( (mA) Supply voltage V Supply voltage V 3.Reference voltage, output current setting pin voltage...
MB3788 (Continued) 8.Gain - frequency characteristic and phase - frequency 7. Duty - input oscillating frequency characteristic characteristic Input waveform = 6 V = +25 C 1.9V = 1.6 V 1.3V = +25 C Duty Gain Phase Dtr (%) (dB) (deg) -180 5K 10K...
MB3788 HOW TO SET OUTPUT VOLTAGE Note: Set the output voltage in the positive range (V > 0).
MB3788 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: •...
MB3788 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).
MB3788 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 V pin (pin 11).
MB3788 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.
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). characteristic between V and V REF/2...
MB3788 APPLICATION CIRCUIT 10 H 33 F 33 F CTL2 CTL1 4.7 k <Logic power supply> +IN1 (E) 1000 pF 4.7 k 8.2 k Channel 1 -IN1 (E) 22 H (dB) (out) 100 k 0.22 F 2.7 k OUT1 10 F (15 mA) -IN1 (C) <Logic power supply>...
MB3788 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.