Datasheet LTM4602HV (Analog Devices) - 10

LTM4602HV
U U W U APPLICATIO S I FOR ATIO
in the PCB layout to minimize the trace inductance and
Soft-Start and Latchoff with the RUN/SS pin
high frequency AC noise. The RUN/SS pin provides a means to shut down the LTM4602HV as well as a timer for soft-start and over-
Output Capacitors
current latchoff. Pulling the RUN/SS pin below 0.8V puts The LTM4602HV is designed for low output voltage ripple. the LTM4602HV into a low quiescent current shutdown The bulk output capacitor COUT is chosen with low enough (IQ ≤ 75µA). Releasing the pin allows an internal 1.2µA effective series resistance (ESR) to meet the output voltage current source to charge up the timing capacitor CSS. ripple and transient requirements. COUT can be low ESR Inside LTM4602HV, there is an internal 1000pF capaci- tantalum capacitor, low ESR polymer capacitor or ceramic tor from RUN/SS pin to ground. If RUN/SS pin has an capacitor (X5R or X7R). The typical capacitance is 200µF external capacitor CSS_EXT to ground, the delay before if all ceramic output capacitors are used. The internally starting is about: optimized loop compensation provides suffi cient stability margin for all ceramic capacitors applications. Additional 1. V 5 t = C •( + p 1000 F DELAY SS EXT ) _ output fi ltering may be required by the system designer, 1 2 . A µ if further reduction of output ripple or dynamic transient spike is required. Refer to Table 2 for an output capaci- When the voltage on RUN/SS pin reaches 1.5V, the tance matrix for each output voltage Droop, peak to peak LTM4602HV internal switches are operating with a clamp- deviation and recovery time during a 3A/µs transient with ing of the maximum output inductor current limited by the a specifi c output capacitance. RUN/SS pin total soft-start capacitance. As the RUN/SS pin voltage rises to 3V, the soft-start clamping of the inductor
Fault Conditions: Current Limit and Over current
current is released.
Foldback VIN to VOUT Stepdown Ratios
The LTM4602HV has a current mode controller, which inherently limits the cycle-by-cycle inductor current not There are restrictions in the maximum VIN to VOUT step only in steady state operation, but also in transient. down ratio that can be achieved for a given input voltage. These constraints are shown in the Typical Performance To further limit current in the event of an over load condi- Characteristics curves labeled “VIN to VOUT Stepdown tion, the LTM4602HV provides foldback current limiting. Ratio”. Note that additional thermal de-rating may apply. If the output voltage falls by more than 50%, then the See the Thermal Considerations and Output Current De- maximum output current is progressively lowered to about Rating sections of this data sheet. one sixth of its full current limit value. 4602hvf 10