 |
 |
|
| MIC29150-12WT |
|
|||||||||||||||||
 MICREL
|
| |||||||||||||||||
|
18 page 
Micrel, Inc. MIC29150/29300/29500/29750 January 2012 18 M9999-013112-B Capacitor Requirements For stability and minimum output noise, a capacitor on the regulator output is necessary. The value of this capacitor is dependent upon the output current; lower currents allow smaller capacitors. The MIC29150/29300/29500/29750 regulators are stable with the following minimum capacitor values at full load: Device Full Load Capacitor MIC29150...............................................10µF MIC29300...............................................10µF MIC29500...............................................10µF MIC29750...............................................22µF This capacitor need not be an expensive low ESR type: aluminum electrolytics are adequate. In fact, extremely low ESR capacitors may contribute to instability. Tantalum capacitors are recommended for systems where fast load transient response is important. Where the regulator is powered from a source with a high AC impedance, a 0.1µF capacitor connected between Input and GND is recommended. This capacitor should have good characteristics to above 250kHz. Minimum Load Current The MIC29150–29750 regulators are specified between finite loads. If the output current is too small, leakage currents dominate and the output voltage rises. The following minimum load current swamps any expected leakage current across the operating temperature range: Device Minimum Load MIC29150................................................5mA MIC29300................................................7mA MIC29500..............................................10mA MIC29750..............................................10mA Adjustable Regulator Design R1 R2 VIN VOUT MIC29152BT 22µF 10µF Figure 4. Adjustable Regulator with Resistors The adjustable regulator versions, MIC29xx2 and MIC29xx3, allow programming the output voltage anywhere between 1.25V and the 25V. Two resistors are used. The resistor values are calculated by: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − × = 1 1.240 V R R OUT 2 1 where VOUT is the desired output voltage. Figure 4 shows component definition. Applications with widely varying load currents may scale the resistors to draw the minimum load current required for proper operation (see “Minimum Load Current” section). Error Flag MIC29xx1 and MIC29xx3 versions feature an Error Flag, which looks at the output voltage and signals an error condition when this voltage drops 5% below its expected value. The error flag is an open-collector output that pulls low under fault conditions. It may sink 10mA. Low output voltage signifies a number of possible problems, including an overcurrent fault (the device is in current limit) and low input voltage. The flag output is inoperative during overtemperature shutdown conditions. Enable Input MIC29xx1 and MIC29xx2 versions feature an enable (EN) input that allows ON/OFF control of the device. Special design allows “zero” current drain when the device is disabled—only microamperes of leakage current flows. The EN input has TTL/CMOS compatible thresholds for simple interfacing with logic, or may be directly tied to ≤30V. Enabling the regulator requires approximately 20µA of current. |
