BD95500MUV Datasheet, PDF (8/21 Pages) Rohm – Switching Regulator with MOSFET for DDR-SDRAM Cores

BD95500MUV
Technical Note
●Pin Descriptions
・VCC (5 Pin)
This is the power supply pin for IC internal circuits, except the FET driver. The input supply voltage range is 4.5V to 5.5V.
It is recommended that a 10Ω/0.1uF C-R filter be put in this pin from VDD rail.
・EN (39 Pin)
When EN pin voltage is at least 2.3V, the status of this switching regulator becomes active. Conversely, the status
switches off when EN pin voltage goes lower than 0.8V and circuit current becomes 0µA.
・VDD (14 Pin)
This is the power supply pin to drive the LOW side FET and for Boot-strap diode. It is recommended that a 1~10µF
bypass capacitor be established to compensate for rush current during the FET ON/OFF transition.
・VREG (7 Pin)
This is the reference voltage output pin. The voltage is 2.5V, with 500uA current ability. It is recommended that a
0.22~1µF capacitor (X5R or X7R) be established between VREG and GND (6 Pin). When REF is not adjusted from the
external voltage supply, the REF voltage can be adjusted using the external resistor divider of VREG.
・REF (10 Pin)
This is the output voltage adjustment pin by resistor divider network from VREG pin (0.7~2.0V). It is also very
convenient for synchronizing external voltage supply. The IC controls the output voltage (REF≒VOUT).
・ILIM (4 Pin)
BD95500MUV detects the voltage between Is+ pin and Is- pin and limits the output current (OCP). Voltage equivalent to
1/10 of the ILIM voltage is the voltage drop of external current sense resistor. A very low current sense resistor or
inductor DCR can also be used for this platform.
・SS/TRACK (9 Pin)
This is the adjustment pin to set the soft start time. SS voltage is low during standby status. When EN is ON, the soft
start time can be determined by the SS charge current and capacitor between SS-GND. Until SS reaches REF voltage,
the output voltage is equivalent to SS voltage. And also this pin enables to operate tracking function. The output voltage
keeps track of a power supply rail by connecting 10kΩ resistance between the power supply rail and SS/TRACK pin.
・VINS (37 Pin)
The duty cycle is determined by input voltage and controls output voltage. In other words, the output voltage is affected
by input voltage. Therefore, when VINS voltage fluctuates, the output voltage becomes also unstable. Since the VINS
line is also the input voltage of the switching regulator, stability depends on the impedance of the voltage supply. It is
recommended to establish a bypass capacitor or CR filter suitable for the actual application.
・FS (8 Pin)
This is the pin to adjust the switching frequency with the resistor. It is recommended that a resistor be established to
GND (6 pin).The frequency range is from 200kHz to 1000kHz.
・Is+ (13 pin), Is- (12 pin)
These pins are connected to both sides of the current sense resistor to detect output current. The voltage drop between
Is+ and Is- is compared with the voltage equivalent to 1/10 of ILIM voltage. When this voltage drop hits the specified
voltage level, the output voltage is OFF. Since the maximum input voltage is 2.7V, set the output voltage by the
resistance division value in case the output voltage is 2.7V or more.
・BOOT (38 pin)
This is the voltage supply to drive the high side FET and a Diode for BOOT strap function is built in. The maximum
absolute ratings are 30V (from GND) and 7V (from SW). BOOT voltage swings between (VIN+Vcc) and Vcc during
active operation.
・PGOOD (1 pin)
This pin is output pin for Power Good. It is open drain pin and recommended to connect to other power supply through
the pull-up resistance (about 100kΩ).
・CE (3 pin)
This pin is for the ceramic capacitor. It is useful to utilize low ESR capacitor for output capacitor.
・MODE (40 pin)
This is the control mode changeable pin. The status is Low : continuous mode, the status is High : SLLM^TM.
・VOUT (11 pin)
This is the monitor pin for output voltage. This IC controls the voltage in the status of REF≒VOUT. When output voltage
is required 2V or more, set the output voltage by the resistance division value.
・SW (22-29 pin)
This is connected pin for coil. SW voltage swings between VIN and GND. It is recommended to connect by heavy and
short pattern to coil.
・VIN (31-36 pin)
This is input power supply pin. Recommend input voltage is 3.3V to 20V. Connect the input capacitor against PGND
directly.
・PGND (15-21, 30 pin)
This is power ground pin. It is recommended to connect by heavy and short pattern. Connect in reverse side of IC when
connecting to GND (6 pin).
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2010.05 - Rev.C