HA16116FP Datasheet, PDF (11/34 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16116FP/FPJ, HA16121FP/FPJ
To Vref
V_TH
V_E/O
V_DB
C_T
PWM
comparator ^VIN
V_TL
−
V_DB ^{R1 E/O}
DB
+
+
5k
Booster
channel
On
t_OFF t_ON
Off
PWM
C_{ST R2}
From UVL _0.8V
pulse
output ^Step-down/
inverting
Off
channel
On
T
1.6 V typ
1.0 V typ
V_IN
GND
V_IN
GND
Figure 3.1 Dead Band Duty Setting
3.2 Soft Start (SST) Setting (each channel)
When the power is turned on, the soft start function gradually raises V_DB (refer to section 3.1), and the
PWM output pulse width gradually widens. This function is realized by adding a capacitor C_ST to the DB
pin. The function is realized as follows.
In the figure 3.2, the DB pin is clamped internally at approximately 0.8 V, which is 0.2 V lower than the
triangle wave V_TL = 1.0 V typ.
t_A: Standby time until PWM pulse starts widening.
t_B: Time during which SST is in effect.
During soft start, the DB pin voltage in the figure below is as expressed in the following equation.
−t − t_0.8
V_SST = V_DB ⋅ 1 − e T , t_SST = t_A + t_B
Here,
t_0.8 = −T ln
1 − ^0.8
V_DB
,
T = C_ST ⋅ (R₁ // R₂)
How to select values: If the soft start time t_SST is too short, the DC/DC converter output voltage will tend to
overshoot. To prevent this, set t_SST to a few tens of ms or above.
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