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S-85S1PD07-I8T1U Datasheet(PDF) 9 Page - Seiko Instruments Inc |
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S-85S1PD07-I8T1U Datasheet(HTML) 9 Page - Seiko Instruments Inc |
9 / 38 page POWER MONITORING OUTPUT, 5.5 V INPUT, 200 mA SYNCHRONOUS STEP-DOWN SWITCHING REGULATOR WITH 260 nA QUIESCENT CURRENT Rev.1.3_00 S-85S1P Series 9 Operation 1. DC-DC converter block 1. 1 Fast transient response Distinctive COT (Constant On-Time) control is used for DC-DC converter control. The S-85S1P Series monitors the output voltage (VOUT) using a comparator and if VOUT falls below the targeted value, the high side power MOS FET will turn on for a certain amount of time. Since the high side power MOS FET turns on and VOUT rises immediately after the load current fluctuates rapidly and VOUT falls, the fast transient response is realized. The S-85S1P Series outputs ON time in proportion to VOUT and in inverse proportion to power supply voltage. Therefore, when in continuous mode, even if the power supply voltage or VOUT settings would change, it always operates at a quasi-fixed frequency of 1 MHz. 1. 2 PWM / PFM switching control The S-85S1P Series automatically switches between the pulse width modulation method (PWM) and pulse frequency modulation method (PFM) according to the load current. If the output current (IOUT) is large, the IC will operate using PWM control. If IOUT is small, the IC using PFM control, the pulse will skip according to the load current. This reduces switching loss and improves efficiency when under light load. The S-85S1P Series has a built-in reverse current detection circuit. The reverse current detection circuit monitors the current flowing through the inductor. If the bottom of ripple current in the inductor falls to 0 mA, the high side power MOS FET and low side power MOS FET will turn off and switching operation will stop. Switching frequency will fall from 1.0 MHz by skipping a pulse. This means that the smaller IOUT is, the more the switching frequency (fSW) will drop, and it reduces switching loss. 1. 3 Ultra low current consumption When in discontinuous mode, the S-85S1P Series reduces current consumption to 260 nA typ. by intermittently operating a control circuit and a protection circuit. When under light load, the high side power MOS FET and low side power MOS FET will turn off. When switching operation stops and a certain amount of time elapses, only the necessary circuits will operate. Under voltage lockout function (UVLO), thermal shutdown function, current limit function, and automatic recovery type short-circuit protection function are prepared in the S-85S1P Series, and each protection function will carry out detection operation for a certain amount of time from when the high side power MOS FET turns on under light load. It is thus able to realize ultra low current consumption. When under heavy load, the IC changes to continuous mode as a result of the fact that the high side power MOS FET and low side power MOS FET turn on continuously, so all the IC, including the protection circuits, will operate. 1. 4 EN pin This pin starts and stops switching operation. When the EN pin is set to "L", the operation of all internal circuits, including the high side power MOS FET, is stopped, reducing current consumption. Current consumption increases when a voltage of 0.3 V to VIN − 0.3 V is applied to the EN pin. When not using the EN pin, connect it to the VIN pin. Since the EN pin is neither pulled down nor pulled up internally, do not use it in the floating status. The structure of the EN pin is shown in Figure 3. Table 8 EN Pin Internal Circuit VOUT Pin Voltage "H" Enable (normal operation) VOUT *2 "L" Disable (standby) "High-Z" *1. Refer to *2 in Table 6 in " Electrical Characteristics". VIN VSS EN Figure 3 |
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